Making Doctor Who Great Again Part 1 - Cosmology/Tiering

ByAsura · Dec 26, 2023

See here for TL;DR.

Edit: Also, see here for a some small clarifications and new info.

Since I can't post threads with more than 150,000 words, I will continue this in the comments.

I'd like to thank the people in the Doctor Who Discussion Thread for helping me with this thread, especially @Oliver_de_jesus, @Udlmaster, @Quasar002, @Doxten_, and @Lord_Farquaad69420.

Introduction

Almost all of our higher-dimensional tiering comes from a somewhat nebulous quote in Bernice Summerfield and the Infernal Nexus and Craig Hinton's novels. Doctor Who and its spin-offs have 60 years of material to cover, so we're basically treating a needle as the entire haystack. Also, higher-dimensional tiering should be presented on a case-by-case basis due to inconsistency.

Besides that, I don't really have a certain rating or full conclusion in mind. My plan is simply to wax lyrical about the cosmology and see what ratings can be achieved.

Bernice Summerfield and the Infernal Nexus

The author stresses that multiverse is used in place of universe, and vice-versa.

It’s another common misconception, held by those who hold such things, that our so-called universe - everything we know of and can ever know - is just one facet of a larger Multiverse. Which shows how much the people who hold things know, part of which is certainly not basic English, since there can by definition only be one universe, of which all putative multiverses must necessarily be a part. People who can get something so simple the wrong way round are probably the last people to ask about comparative ontology, so we’ll leave them in a handy off-term student bar between panels, discussing the minutiae of their costume-parade insignia, the finer points of conversational Klingon and the aerodynamics of fictional dragons. There may be a disco later, but you probably wouldn’t want to go.

In fact, alternate realities seemingly don't exist at all.

The differing realities of actual multiverses are nothing like as simple as, let’s say, alternate worlds produced by Nazis winning wars or presidents not getting shot - none of which have or will ever have existed save in potentia.

He doesn't say 'none of which have or will have existed in the universe', simply say they don't exist. 'Save in potentia' probably just means that it was possible, not that it happened/exists (which it would also mean in virtually any other circumstance, i.e 'it's not really possible to speak with your father, save in potentia').

When the Tinker's Cuss was exposed to some energy during an experiment, it was partially knocked at a right angle out of their multiverse (aka, the normal Doctor Who universe) and into a different multiverse/dimensional set.

‘I think what our visitors are trying to say,’ [...] ‘is that the Tinker’s Cuss was hit by some primal, transmutational energy. [...] The force of discharge knocked the ship off its dimensional axis. Rupert, Igron and their team were saved by the force fields around the science deck, designed to protect their apparatus, so only that part of the ship remained in our own dimensional set...’
‘The upshot is,’ said Braxiatel, ‘that we now have an extraordinarily advanced research vessel lying derelict and in a transdimensional state [...] What we need, Bernice, is someone to retrieve it - someone, if possible, who has had direct experience with the more abstruse transdimensional states.’
The best bet was to realign her own ship with the dimensionally-displaced bulk of the science vessel, set up the portable field generators and use them, basically, to drag the Tinker’s Cuss back from a right angle to reality.
‘Of course, the problem is that - as I do believe I’ve mentioned - humans from your own particular multiverse are a scarcity here. That makes you something of an unknown quantity [...]'

Multiverses are 'metadimensional subsets' and 'substrative quantum states' that exist 'somewhere else'.

‘So which human multiverse is you from?’ [...] ‘Which ones have you got?’ [...] ‘Is you got big holes in rock with light shining in or is you got great big balls?’ [...] ‘We call them planets. They go round suns, mostly.’ [...] ‘Is you got stuff to breath everywhere or is only on big balls what are called planets?’ ‘Only around some of the planets,’ said Benny. ‘Ri-ight. Is all things expanding from humongous explosion, staying in same place or going smaller into little bitty thing?’ ‘It’s expanding from the Big Bang,’ said Benny, though apparently at some point it’s going to start to...’ ‘[...] Is the most prevalent matter in your particular metadimensional subset that of monatomic hydrogen?’
‘Lucien di Vasht, [...] is of course one of the most powerful men in the substrative quantum state-vector designated seven four one point three oh four, forward slash, five nine zero, slash, upsilon kappa four one nine three seven four nine six one...’
Nor can they be properly expressed, as such, in terms of additional dimensions, molecular resonances and quantum-packet signatures, which exist only in the minds of lazy science- fiction writers. In fact, the only human mind to ever come within striking distance of accounting for them was that of Dr Rupert Gilhooly, who described them in a string of equations large enough to fill three phone books (Business and Residential), which only he could understand, and which he expressed for everyone else as: ‘Just like these other places, yeah? They’re just, like, somewhere else.’

At last count, there were 417 multiverses, each with vastly different laws of physics. For reference, station control exists in a nexus between multiple multiverses and dimensional sets.

There were four hundred and seventeen of these multiverses at the last count, each of them existing on their own terms, in radically different states, and Station Control exists as a nexus point between them.
The space she fell through could have been anything from precisely her size to infinite - probably both, in a technical sense, since she seemed to be the only thing in it...
'That would be stupid. Frankenstein was a fictional character invented by Mary Shelley. You only find him and his monster in the multiverse which picks up archetypical resonances from all the others. There’s a world of lycanthropes, I suppose, which people get mixed up with stories of werewolves, vampires and zombies...’ ‘Oh my,’ said Bernice. ‘Worlds still ruled by the dinosaurs?’ [...] ‘One or two.’ ‘Worlds where the gods really exist?’ ‘Something like that. And you wouldn’t want to take their names in vain, believe me. They have a nasty habit of turning up.’
One of the things that annoys the inhabitants of what are called the Infernal Regions is the assumption that their multiverse looks like a molten lava bed as drawn by Ernst. The fact that their multiverse consists of bubbles in endless rock, they point out, misses the point. The point being the sheer size of said bubbles. The bubble-worlds themselves are quite big enough that the nature of them is no more evident than the planetary nature of a picture-book English landscape. The bubble worlds had land and sky just like everyone else, produced any number of different terrains.
[...] ‘Besides, from what I’ve heard, the only actual creature that ever evolved to resemble Santa Claus was a really nasty predator called the Snata - over in a multiverse that looked like a massive orrery or something - and it became extinct when that multiverse collapsed on itself.’ [...] ‘An entire multiverse built like an orrery? That’s just stupid.’ ‘Suit yourself.’ Jason shrugged yet again. ‘I must admit, I’m not sure if the equivalent of planets were the birds themselves or being carried by them.’ Benny was about to enlighten her ex-husband as to the difference between the word ‘orrery’ and ‘aviary’ when she realised that they were approaching a large and ornate set of arched doors, which were swinging open of their own accord.
With the rest of the Tinker’s Cuss now in some halfway congruent reality, the dimensional stresses around the bitten-out section of the science-deck -the lethal forces that Benny had noted when she had first arrived at these spatial co-ordinates - had dissipated.
It was like a planet colliding with a world the inhabitants knew to be flat. (The analogy falls down a little, of course, since there are multiverses where the world is indeed flat, and where the stars are gemstones in the mantel of a crystal dome.)
‘Swamp-lobster from the Vehicular Protectorates,’ he said. ‘One of those places where the whole multiverse is just a single flat world - endless swampland and marshes covered by a network of autobahns, apparently. They’re quite a delicacy, so they say. The lobsters I mean, not the autobahns.’
Marpies came from a multiverse where physical laws were more as they were thought to be than an immutable system of cause and effect. Birds and bees flew, quite simply, because they were too stupid to know that they couldn’t- and all a man needed to be able to fly was a form of lobotomy which quite literally turned him into a birdbrain.
The first thing Bernice saw was the ship itself, the previously visible area of it now had a huge bite taken out of the hull. The science ship was a mess, plating sheared and sharded from the twisted frame, debris hanging in the black of a space no different, visually, from the three-dimensional space she’d left.
In the mutable chaos of Station Control there was a place where, after a fashion, things remained constant; the foundation upon which the features of the Station were built in the first place to shift and change. In abstract terms one might think of it as the basic hardware of a computer on which the files, applications and entire operating systems can be loaded, updated and, if it’s running exactly according to the instruction manual, bring the whole lot crashing down every three and a half minutes. It was not that this base state was immutable, but any change required the equivalent of taking the back off with a screwdriver - a completely different order of effort. In reality, such as it was, it was more akin to the sewers running under a city, the decomposing mulch on a forest floor, the piles of guano that accumulate at the bottom of a cliff populated by sea birds. Direction it could be said had no meaning, hereon the Station, but this base state was commonly, if not universally known as the Underland. A place where if you fell, in any number of senses, it was where you ended up.
Differing entropy-slopes, causal processes and the fact that something as basic as atoms might or might not exist, in a certain sense, made problems with incompatible phone sockets and the like the least of anyone’s worries. Visually, the brastifranivisor looked like a cross between a miniature steam engine and a valve-radio, although that would also have to factor in a strangely organic quality, as though the things had aspects of some quite repulsive-looking living matter that existed in dimensions other than the purely visible.
When she came to try and describe Station Control, somewhile later, Bernice would find herself coming up against an almost insurmountable problem. How do you describe sheer chaos? If you describe it on an instant-by-instant basis, try to detail discrete images and sensations from a barrage of them, you end up with something like: Item: a small collection of multicoloured weevils, sitting on a little tarmaline plinth with ambulatory legs, bouncing around in complex patterns reminiscent of the Georgian State Dancers as seen from a great height. No particular reason for their perpetual dance is apparent. Item: sections of wall, ceiling and floor which are both sides of themselves simultaneously, rather like those wireframe representations of a cube of which one can be looking at the top or the bottom, depending upon what the mind decides, but in several additional dimensions. Item: a sudden tingling in the head and the blindingly obvious idea that is instantly gone, save for the deep knowledge that the idea itself was alive, a living memory which has passed through you on the way to somewhere else, rather like a man hurrying up a street. Item: the smell of camphor and tulips which, once again, you sensed was in some way alive - as alive as all the more prosaic giant insects, walking bears, tentacular slime monsters and all the possible variations on the basically humanoid (or at least bipedal) creatures milling in their thousands through complex spaces where down might be up or inside-out, where apparently direct routes twisted back in on themselves like a Mobius strip, where you could travel from one physical zone to another merely by thinking about it, or be barred from a section of apparently clear space by the mind registering, on some primal level, that said area was utterly inimical to life as we know it and so reacting, purely psychosomatically, as if one has walked into a diamond-hard plexiglass wall...In the end, Benny would be forced into simplification, in much the way that you can simplify the complex molecular interplay of one substance dissolving into another as a ‘swirl’. The interior of Station Control could, in the end, be described as a collection of enclosed places of various sizes -call them chambers - to which there were entrances and exits and conduits between. Forget all the infinite variety of the distinctions unless it was important. Call them that and be done with it.

Dimensional sets aren't different worlds, just directionally separated. And even if you could cross them, you're bound not to go anywhere useful.

There is a common misconception, incidentally, that a different dimensional set is the same thing as another world. This simply isn’t so. Dimensions are indeed involved, but in the same way that one can point in the general direction of the United States of America from the Republic of Ireland, but it is as impossible to actually do anything with dimensions as it is to cross the North Atlantic on foot. To stretch the metaphor to breaking point, human technology in this area was on the level of a leaky coracle: it was possible to displace things transdimensionally, but the chances of being displaced into anywhere useful was of the order of one in several billion. This might seem odd in the face of all the stories of those travelling to weird and wonderful dimensions, but the fact is that those people were the one in several billion, or were taken there by some inhuman agency, or were quite frankly lying through their teeth.
‘And besides all that, do you know which direction our own world is in? Exactly? I certainly don’t. Twist into the general dimensional set of the Station and automatic processes cut in to take you the rest of the way; without fixed and precise co-ordinates going the other way you could end up... and here we are.’
‘That’s the dimensionally-mutable nature of the Station,’ Jason said. ‘Things can contain other things bigger than themselves, a bit like onion skins but in a different direction. Things can be bigger on the inside than out.’

Bernice Summerfield later realises that she's passing through a third dimensional axis plus an infinite dimensional set of time.

She would never have a clear memory of the feelings that followed -feelings that the human body was never meant to experience and with which the human mind was ever meant to cope. Intellectually, she knew that she was merely rotating through the extradimensional axis that three-dimensional beings do all the time - the three dimensions plus Time that we know being only three-plus-Time of an infinite dimensional set - without even knowing it.

Transdimensional travel causes people to change age because they're in different timelines.

‘When the rift sealed itself up,’ said Jason, ‘there was this period of flux, with the world transforming around me over and over again. I have no idea how long it lasted. It was like I’d pop into these whole different worlds and do stuff and then they’d change around me again. At the time it felt like I was spending weeks or months in those worlds, and I’d come out with the memories of it, but I’d come out no older and physically unchanged...’‘The Gilhooly Theory of Transdimensional Contrivance,’ said Bernice. ‘Do what?’ said Jason. ‘You wouldn’t know about it,’ Benny said. ‘It was after you went away. Dr Rupert Gilhooly was trying to explain it on some holovid chats how or other, the interviewer said something like, “oh come on, that sounds like the sort of contrivance you get in crappy old adventure stories to explain why the heroes always seem to stay the same age”, and the name just sort of stuck. It just means that if you end up dislocated in time or in some other dimension, the physical processes of ageing go on hold because you’re not on your own timeline.’

Could this mean that N-Space has infinite spatio-temporal dimensions? I think it could, but I'm not sure we have explicit proof that dimensional sets are spatial dimensions, or that they have a degree of dimensional superiority. I even tried to contact Dave Stone to get some answers about this (which I've never done before, and probably will never do again), but he didn't answer.

Higher Dimensions

Examples

Barring the omniverse and the After-Universe, the highest individual domains in the multiverse and N-Space alike are currently 11-D (I think the problem there should go without saying, ngl). My aim is to show the examples of either multiversal or universal caps below 11-D, examples of 11-D, and instances of said cosmologies exceeding 11-D.

10-dimensions

Tomb of Valdemar

Moon Graffiti (at least)

The Death of Art

11-dimensions

Millennial Rites (there was a >30-D database, but it was a special case because it took place in an alter-time realm with 3 different laws of physics)

Lucifer Rising

The Crystal Bucephalus

Parasite

Autumn Mist

Unnatural History

The Quantum Archangel

First Frontier

>11 dimensions

Logopolis

Infinity Doctors

At Childhood's End

Cat's Cradle: Time's Crucible

Thirteen Doctors, Thirteen Stories: Spore

Meanwhile In The TARDIS

End of the Line

Short Trips: Time Signature: The Hunting of the Slook

11th Doctor Year 1 #2

The Brakespeare Voyage

So, in terms of dimensional tiering, an 11-D cosmology is the mode, but a similar number of sources as a whole give a different number (whether it's 3 or infinity). This probably isn't all of the sources out there, though.

Inconsistency

In fiction, spatial dimensions are often presented as planes of existence (such as universes, in and of themselves) rather than quantities. Doctor Who is no stranger to this.

In Tales of Terror: Living Image, the 4/5th dimensions are much larger than 3, and 4th dimensional beings (let alone 5-D) effectively see humans as spatially flat. This is also true for the higher dimensions/entities in Lucifer Rising and Autumn Mist.

‘There are all manner of abstract creatures we don’t even know about yet. Entities that stalk the gulfs of the Space–Time Vortex, beings unlike anything you’ll have ever known here on Earth. They exist in five dimensions all at once; they’re here and yet they’re not here.’ [...] ‘But how can that be?’ asked Nathan. ‘How can we not see them?’ ‘Because they exist in a different dimension,’ explained the Doctor. ‘Think of it this way: we’re three-dimensional beings, yes? We exist. The pictures you paint are only two-dimensional. They also exist. And yet, the subjects you depict in your paintings couldn’t even begin to conceive of a third dimension, never mind a fourth or even a fifth!’ ‘So you’re saying we’re basically stickmen?’ Ace suggested, not very helpfully. ‘But no, those phantoms …’ Nathan was struggling to process what the Doctor was saying. ‘They came for me. They know me!’ ‘Not at all. Just insubstantial glimpses of a dimension beyond our own. But the fact we can see them means they’re getting closer. They’re growing stronger, minute by minute, and I think it’s thanks to you, Mr Gough.’
‘I’m allowing you the chance to walk away,’ the Doctor said. ‘You don’t need Earth. You don’t even need our dimension. You have the entire Vortex at your disposal: the fourth and fifth dimensions of space and time!’ ‘THESE DIMENSIONS ARE INSUBSTANTIAL!’ raged the creature. ‘WE SEEK PHYSICAL FORM!’

‘There aren’t seven dimensions,’ Ace exclaimed, and then added, ‘are there?’ ‘The space-time continuum has eleven dimensions,’ Legion replied, ‘although four of them are inaccessible.’ ‘So, what’s it like then, living in seven dimensions?’ [...] ‘But imagine, if you are able, watching small creatures floating on the surface of a pond. Imagine that these creatures cannot look up or down, but only across the water itself. They are not aware of the air, or the depths. Their world is flat.’ As it talked, Legion’s voice changed. The various elements combined until it seemed to Ace that a choir was whispering to her. ‘You reach down from your exalted position, beyond their understanding, and put your – the things on the ends of your forelimbs...’ ‘Fingers.’ ‘...fingers into the water. What do these creatures see?’ After a few seconds, Ace realized that this was not a rhetorical question. ‘Er... My fingers?’ ‘No, because your fingers exist in three dimensions, and they can only perceive two. They see...’ It paused. ‘How many fingers do you possess?’ [...] ‘Then these creatures see five discs suddenly appear in the water. As far as they are concerned, these discs are five separate entities. Why should they associate them with each other? But if you plunge your hand deeper into the water, up to the – the hinge section...’ ‘The wrist.’ ‘Up to the wrist, then the creatures who inhabit the surface of the water will see the five discs suddenly merge into one large ellipse. Do you understand?’ [...] ‘And if you pick one of these creatures up and place it a little distance away on the surface of the water, all its fellows will see is that it vanished, and reappeared elsewhere. Neither they, nor it, can see the air through which it moved. Do you understand?’ ‘Uh-huh.’ ‘What you see of me,’ and the hairy, three-legged blob standing at the front of the table stretched like hot toffee and broke apart into fifteen warty blue spheres which bounced, very slowly, between the floor and the ceiling, ‘is merely a three-dimensional cross-section of a seven-dimensional shape. As my body moves in and out of your perception, you see different aspects of it. Your three-dimensional brain is not capable of appreciating the beauty of my true body.’ [...] The spheres coalesced into a black and vaguely hairy shape that threatened to develop three thin and multi-jointed legs.

But, characters in Unnatural History (literally the novel preceding Autumn Mist) state that higher-dimensions are flatter than 3-dimensional space.

‘I’m afraid the higher dimensions aren’t very wide in three-space terms,’ said the unnaturalist. ‘We’re going to use fractal dimensional compression techniques on you. The effect is disorientating, I’m told.’
The unnaturalist paid him no mind. ‘And it is only one specimen among the many which have been drawn here by the anomaly. Creatures from outside my people’s limited reach into the higher dimensions.’
Only someone who comprehended the higher dimensions could have removed those tags. Griffin had a fair idea of how it might be accomplished, using the biodata strands themselves.
‘There’s much more to Griffin than meets the eye, quite literally,’ the Doctor explained. ‘He comes from our three-dimensional universe, but he’s also at home in the higher dimensions. Four, five, six. . . He’s like a sphere visiting a world full of circles. We can perceive part of him – to us, he looks like another circle – but he also sticks out above and below our sheet of paper.’ So that was why he seemed to have too many hands, Sam thought. How he could move stuff around inside them. ‘So our current understanding is wrong?’ Kyra was saying. ‘Normal space isn’t three-dimensional?’ The Doctor waved his hand, the wires in the device rattling about. ‘It’s a bit more complicated than that,’ he said. ‘Don’t worry, the basic maths will be worked out in a century or two.’ Kyra nodded, as though that was that taken care of. ‘Ordinary walls wouldn’t be able to hold him – he’d find a way, the right angle to just slide out of any cage, any cell.’

Some stories present dimensions as planes and directions simultaneously.

‘Time travel occurs in relative dimensions. Weren’t you listening before? A TARDIS can travel into the past and future, but not its own past and future. That would be a theoretical absurdity.’
‘Warning, master. Alien species identified. It is the Vore. By Supreme Council order, date index 309456/4756.7RE/1213GRT/100447TL, no Time Lord is to engage the Vore, all time ships are to observe an exclusion zone no less than one parsec and one century, in all five directions from any Vore moon.
The Time Lords were losing. This was a war fought in five dimensions, across the whole of time and space. - The Gallifrey Chronicles

‘When the universe was created, dimensions started to solidify out of the primal chaos. But five got there first –the three spatial dimensions and two of time.’
‘At the risk of sounding like a high-and-mighty Time Lord, I am a high-and-mighty Time Lord. And to quote one of my elementary texts in the matter: “And in the aftermath of Event Zero, eleven dimensions did fight for existence. Five were triumphant – together they did become the three dimensions of space, and the two dimensions of time through which we travel. But the remaining six dimensions did still exist: although beaten, although denied their dominance, they curled and curdled amongst themselves to become a six-fold universe, separate yet conjoined.
The knots of Calabi-Yau Space, existing at every point in the four familiar dimensions of space-time as well as throughout the time vortex, were inaccessible to the majority of races in the cosmos. Even the most advanced of them treated it as an abstract set of solutions to some esoteric quantum equations.
‘The time vortex is the second temporal dimension – it’s the region through which TARDISes travel, the region that TOMTIT creates a gap through to enable matter transmission. When the dimensions froze out of the void it became inexorably linked to Calabi-Yau Space. - The Quantum Archangel

One of the most inconsistent examples is Tomb of Valdemar.

„The higher dimensions are undetectable. Even for the TARDIS. There‟s no instrumentation built to perceive them. ‟The Doctor keeps grinning. „Has anyone told the higher dimensions that?‟
„A release of trans-dimensional energy,‟ she mutters to herself. „The result of a rift between the lower and higher dimensions of matter. A rift in the kinetic dance. In theory.‟
„The higher dimensions,‟ whispers the Doctor. „How could they... affect a machine?‟ „Almost nothing is known of the higher dimensions,‟ says Romana. „Except that they exist... co-exist with this universe. A part of reality...‟„A part!‟ The Doctor finally releases her. „They are reality! Total reality! More reality than even pompous Time Lords can perceive. Somehow, it‟s made itself apparent here.‟
„Reality would begin to change,‟ he muses, looking up at the data cylinders lining the walls. „Or more strictly, appear to change. The higher dimensions are reality, just a greater reality than we can perceive. Even Time Lords, with their occasional insights into the fourth and fifth dimensions, aren‟t immune to their effects. You recall that poor man inside the tomb?‟
The Doctor‟s face is in shadow, but she could swear the lines on his face had deepened. He seems older, old as his years. „To breach the higher dimensions,‟ he says. Romana is shocked. Really shocked. „But... but that‟s impossible. The whole idea, that‟s ludicrous.‟ The Doctor laughs, but without humour. „Why are you so upset? Because the Old Ones did it? Or that they achieved an engineering miracle not even the Time Lords could manage?‟ „The experiment was closed down. The Dimensional Ethics Committee...‟
„The mind and body adapt to exposure to the higher dimensions. Organs in the brain, dormant for centuries, begin to grow. The eyes...‟ [...] That certain individual forms of life are more adapted to perceive the higher dimensions? It‟s a childish conceit. Like the idea that certain privileged families could control and master some universal force...‟
„Too dangerous, you see. Three-dimensional life...‟ He sits up and looks at her, thinking something through, „... even four-and five-dimensional life, is unable to perceive the higher dimensions. We lack the necessary sensory apparatus. I mean, there are theories that suggest that these organs lie dormant in the brain but... ah!‟ [...] Telepathy! Perhaps that explains telepathy and why only certain people are rumoured to have the gift. Perhaps the sensory organs in some individuals are better developed. I suppose it‟s possible that telepathy, in fact all psychic phenomena, are utilisation of the forces of the higher dimensions.‟
The Doctor regards Neville and his guards. With the vaccine or whatever it is running through him, he has penetrated the illusions created by the higher dimensions.
„The infiltration and transformation of your mind. Without this fluid, your brain won‟t be able to cope with the shock of regrowing receptors for the higher dimensions. Already your physical forms are changing. Very soon you‟ll either die or go mad. In your case, madder.‟
The Doctor tries for the last time. „Neville. I‟m trying to help you. All I‟ve wanted to do since I got here is help you. You‟re making a terrible mistake. The higher dimensions are inimical to all life. All. Including yours and all your followers.‟
This is no time for rumination. He must be active; he must concentrate fully on the task in hand. Forget the Key to Time. If the higher dimensions are released, time will cease to exist.
The children – twisted, deformed and full of bullets. And others in amongst them. Neville‟s guards, their wounds and the effects of the higher dimensions reshaping their faces and bodies into new, unrecognisable forms. But no Neville or Romana.
„I believe the effects of the higher dimensions stored in the palace are altering our beings.‟
„I don‟t understand.‟ She lifts her head and opens her eyes again for the first time in what seems like ages. The world around her is not the world she remembers. Like a badly tuned picture on a viewing screen, the solid world is being consumed in a blur of static. Only the Doctor remains whole, corporeal, a brightly coloured fly crawling across the screen. Of course – the vaccine, the vaccine. „Is it possible that the higher dimensions is a place in its own right after all? No, not a place – a realm. Impossible, of course, but we haven‟t had breakfast...‟
Two heads, two bodies, fused into one by some odd process known only to the mocking higher dimensions. It climbs back into our universe and howls with the pain of birth.

Conversely, All-Consuming Fire presents folding higher dimensions as a relatively easy and benign concept.

'I have no expectations, therefore nothing that occurs in the world is a surprise. But, if it makes you feel better, the mathematics of folding higher dimensions are relatively simply. I am currently writing a paper on the subject. Perhaps I could send you a copy?'

There are more examples, but I feel the point is made, and there's more evidence above and below this section anyway.

The first example of intermediary dimensions is The Space Museum. The TARDIS accidentally jumps a time track, and ends up in a fourth dimension. They have to escape by travelling to a very specific point in space-time.

VICKI: Time, like space, although a dimension in itself also has dimensions of its own. [...] Yes, you see, we really are in those cases, but we're also standing here looking at ourselves from this dimension.
BARBARA: Well, it's horrible. Those faces, our faces, just staring.
IAN: Well, at least it explains what's been happening to us.
DOCTOR: Yes, it does, my boy. And if we're not there, we can't leave footprints, and break glasses, or touch things.
IAN: And nobody can see us. I see.
DOCTOR: Oh yes, they can. Oh yes, they can see us where we really are. There. [...] You know, I don't mind admitting, I've always found it extremely difficult to solve the fourth dimension. And here we are. Face to face with the fourth dimension. You know, I think the Tardis jumped a time track and ended up here in this fourth dimension. [...] All we have to do is to wait here until we arrive. [...] You see, my dear, before they actually put us in those glass cases, we must have arrived here sometime in the Tardis. These people saw us and thought we were worthy people to be put in their Space Museum. [...] But nothing has happened to us yet. What we are doing now is taking a glimpse into the future, or what might be or could be the future. All that leads up to it, is still yet to come.
VICKI: Doctor, look. Why don't we go and find the Tardis, the real one I mean, and get into it and get out of here now?
DOCTOR: And end up one day, my dear, like that? No, we must not. We've got to stop it happening.
IAN: Doctor, when will we arrive?
DOCTOR: I don't know, my boy, I can't be certain. You see, I'm quite unable to measure the time dimension that the Tardis jumped. But you'll notice we're all wearing the same clothes. So, it could be in a few moments, or a few seconds.

Numerous intermediate dimensions support the space-time continuum.

PERI: What anomalies, Doctor?
DOCTOR: Absolutely nothing to worry about. Few degrees of epsilon inversion in the secondary dimension seven. Call it a gravity hiccup.
PERI: Doctor, you're not making any sense.
DOCTOR: Sorry. I'm going to need to sit down and explain this. Oh, a throne. How very appropriate. There we are. You see, what happens is, you get a prolapse inside one of the supporting dimensions that sustain the space-time continuum. Well, if you imagine a four dimensional sphere
PERI: Frankly, I can't.
DOCTOR: It's a little complicated. Start with a three dimensional object like er, that thing over there.
PERI: Oh, that's Simon's. His papier mâché head.
DOCTOR: Pass it over. Thanks. Now, imagine this object with its time line extended. Oh. What exactly is this?
PERI: It's meant to be a sand creature. But you're wandering again.
DOCTOR: Wondering where this came from. Exhibit B. So this would be the same small boy who gave you Exhibit A?
PERI: The shell thing in the tea caddy? Yes. Simon.
DOCTOR: So, Simon creates Exhibit B after finding Exhibit A. Hmm. Now wait a minute, I should have an elastic band here somewhere. Ah, yeah, here it is. Now, we just secure this caddy to make sure the lid doesn't come off. Now, I'll take the head, you take the caddy. Guard this with your life, and follow me. Catch! [...]
DOCTOR: Ah, the rose garden. So, you see, Peri, the whole thing is probably a transient natural freak. Except, of course, for Exhibits A and B. This sand creature head and your shell thing in the caddy.

STREAM: Stop, I command you. This machine taps the seven concealed dimensions. You'll rupture the very strands of space.

STREAM: Now that I command the intermediate dimensions, nothing can stop me taking complete control over all space and time. Becoming all space and time. Thanks to the power of the Tardis, the circle is mine! - The Hollows of Time

Time and space are relative dimensions. Everything has a dimension of meaning. For example, mimetics are a dimension in addition to the 'basic four' (later confirmed to be the spatial dimensions), and damaging them can remove physical individuality and self-awareness.

In addition to the mundane dimensions, there are others. The most important of these is the mimetic. Everything has a dimension of meaning. The damage that the Cancer Empire had wrought to this world was to its mimetic underpinnings.
The results could be seen visually but could not help but cause the kind of physical distress I suffered on first exposure. Switching my optics allowed me to see it in terms that would not cook my sense of self.
A looming figure stepped into the entrance of the alleyway, taller and wider than any ordinary Jonah. It was a press-gang. Five or six ordinary men and women, mimetically reduced to a point where they could not function as individuals, melded into a single entity. Its appearance changed continuously as it moved. Every shift in angle brought a new face to light as others slid out of view, its appearance depending on which aspect was in sight. As it strode towards me in the alley, I tried to dart past its side to the street behind it. It had the aggregate speed of its original constituents though and easily snatched me as I passed. I struggled, but it had the combined strength of many men as well.
They had followed me and stood before me, side by side. The first one had taken the opportunity of my distraction to remove his helmet. I now saw just how ill he was, and not in any biological fashion. The dimensions, the basic four, the dimension of meaning, together they form the structures with which we are familiar, buildings, people, cultures, the Ship itself, but they can be separated. There can be meaning without matter, like a shadow weapon. There can also be matter without meaning. That is what these men were, material husks, robbed of the significance of their true biodata and reduced to crude animations.
The teaching cell operated on a combination of dimensional and mimetic principles. It pulled in a portion of the world and changed its relationship to the rest of reality. It cut off those inside from any outside influence and vice versa. While you were in the teaching cell, as far as the universe was concerned, you did not exist.
Think of the universe for a moment as having three additional directions (alterward, paraward, and otherward) all at right angles to the ones you know (length, breadth, width and time). - The Brakespeare Voyage

The Relative Dimensions part of the TARDIS acronym refers to its hyper-interior, which is another dimension and essentially a micro-space-time continuum. There's even components named after this fact.

THE DOCTOR: Something disrupting the interface between the relative dimensions. - Blood of the Daleks

HAYTER: That pillar?
DOCTOR: Of course. That's where he's hidden the other passengers.
HAYTER: But it's not big enough.
DOCTOR: Something else for me to explain later.
HAYTER: This revolutionises the whole concept of relative dimension. Oh Doctor, if only I were a younger man and had the time to make use of your knowledge. - Time Flight

DOCTOR 2: Yes, it's quite cozy, isn't it? Oh, you'll soon get used to it, old chap. Relative dimensions and all that. - The Three Doctors

SUSAN: Well, I made up the name Tardis from the initials, Time And Relative Dimension In Space. I thought you'd both understand when you saw the different dimensions inside from those outside. - An Unearthly Child

SARAH: Just how big is the Tardis?
DOCTOR: Well, how big's big? Relative dimensions, you see. No constant.
SARAH: That's not an answer.
DOCTOR: How big are you at the moment?
SARAH: Five four, just, and that's still not an answer.
DOCTOR: Listen, listen. There are no measurements in infinity. You humans have got such limited little minds. I don't know why I like you so much. - Masque of Mandragora

Cosmic blasphemy. Such a move had an inevitable consequence: the complete and utter destruction of both TARDISes. The outer plasmic shells ruptured, the conditional pathways were aborted, the relative dimensions evaporated. - The Quantum Archangel

However, it also refers to the fact that TARDISes travel in relative dimensions. And there's components named after this fact.

DOCTOR: Well, my dear, I'm a doctor of science, and this machine is for travelling through time and relative dimensions in space. - The Massacre

DOCTOR: Well, yes. There's some malfunctioning of the Relative Dimensional Computer.
SARAH: In English.
DOCTOR: It means the steering's gone haywire.
SARAH: Oh - so, we're off course, lost in space.
DOCTOR: Well, yes ... up to a point.
SARAH: And at this speed we're getting loster and loster, thousands and thousands more miles every second.
DOCTOR: Yes. We're sliding with enormous speed in retrograde time. Let's look at the chronometric astrometer. - Exploration Earth

In Auld Morality, The Doctor of an unbound universe describes Imagination and Possibility Theory as 'relative dimensions' (like space and time) that the Time Lords don't explore. These are explicitly confirmed to be dimensions like length, height and width.

He was manipulating just three dimensions at present. How many others were available? He was tempted to seize the Temporal dimension, rolling it back to crush the invaders of his ship that way. He could manipulate the relative dimensions of Imagination and Inner Space-Time to create whatever he liked.
Traversing time as he did, back and forth across centuries of space, rendered the dimension almost meaningless. The Doctor had only occasionally remembered that things needed replacing or servicing, or they wore out completely. Even within the TARDIS, time still took its toll. - Cat's Cradle Time's Crucible

For reference, space is referred to as the fifth dimension in An Unearthly Child, which the author of Time's Crucible frequently references.

SUSAN: I can't, Mister Chesterton. You can't simply work on three of the dimensions.
IAN: Three of them? Oh, time being the fourth dimension, I suppose? Then what do you need E for? What do you make the fifth dimension?
SUSAN: Space.

As I said above, Marnal also states that time travel occurs in relative dimensions. And in the same novel, it's stated that time travel occurs in the fifth dimension (explicitly five directions)—though not space—even outside of the primary mode of Vortex travel.

‘What’s all this about the fourth and fifth dimension?’ Rachel asked. She’d brought a couple of his novels with her to the dining room. If they really contained the secrets of the universe they might be worth struggling through. She’d started on The Beautiful People. So far, though, it was just The Da Vinci Code all over again. ‘Time and space,’ Marnal said. ‘Relative dimensions, you see.’ ‘Oh,’ Rachel said again. Marnal slapped his head. ‘Wait! That’s it! There will be a trail in the fifth dimension.’
‘If they’re time machines, could it be from a time before your planet was – ’Marnal gave her a withering look. ‘Time travel occurs in relative dimensions. Weren’t you listening before? A TARDIS can travel into the past and future, but not its own past and future. That would be a theoretical absurdity.’ Rachel glowered at him, but he was completely oblivious. - The Gallifrey Chronicles
‘Time travel occurs in relative dimensions. Weren’t you listening before? A TARDIS can travel into the past and future, but not its own past and future. That would be a theoretical absurdity.’
‘Warning, master. Alien species identified. It is the Vore. By Supreme Council order, date index 309456/4756.7RE/1213GRT/100447TL, no Time Lord is to engage the Vore, all time ships are to observe an exclusion zone no less than one parsec and one century, in all five directions from any Vore moon.
The Time Lords were losing. This was a war fought in five dimensions, across the whole of time and space.
‘They can move through the fifth dimension.’ ‘I’m not even sure what that means.’ ‘They can manipulate hyperspace corridors. They travel down them like a spider down a thread of silk.’ The Vore pushed them both onwards. - The Gallifrey Chronicles

So, this strongly implies that 'relative dimensions' can apply to planes of existence, spatial dimensions, and mathematical notions (see here for some context).

The Pre-Universe

Christmas on a Rational Planet and Millennial Rites are obviously intended to be the same version of the Pre-Universe, as The Great Intelligence was born there.

Ohh, yes, there were those of the old time who escaped. A handful of baby godlings and ‘great intelligences’... but they were such weak, unimaginative creatures.

In Millennial Rites, Yog Sothoth (aka, The Great Intelligence) is from the universe that predated the Big Bang.

'[...] This Great Kingdom is based on three very different laws of physics: those indigenous to this universe; those of Saraquazel who hails from the universe that follows this one, and those of Yog Sothoth – the Great Intelligence – who is a survivor of the cosmos that existed before the Big Bang. Thanks to Chapel and Anne's meddlings in forces beyond their comprehension, all three sets of laws are fused into an unstable equilibrium. I've got to unbalance that equilibrium, but, at the same time, ensure that all the pieces fall back into the same place that they were to begin with.'

The physics of this universe were immensely different, which grants the Great Old Ones immense powers within N-Space.

'Before this universe was created, there was another one. A totally different universe, with alien physical laws. The heavens were green, and the stars looked like –' He chuckled. 'Giant doughnuts, to be brutally frank. Very, very different. [...]'
'As their universe reached the point of collapse, a group of these "Time Lords" shunted themselves into a parallel dimension which collapsed seconds after ours. Moments later, they erupted into our universe, and soon discovered that they were in possession of undreamt of powers.' [...] 'And I'm afraid that the power went to their heads – or what passed for heads given their new bodies. [...]'

This also extends to their language, Quantum Mnemonics, which became a suped-up equivalent to the mathematics that Time Lords use to create space-time events.

The Doctor brushed the feelings aside and carried on reading what he now realized was the syllabic nucleus of a language that had no place in this universe. The words were derived from a tongue that had been both ancient and arcane before the first stars had ignited in the cosmic firmament, before the first protons and electrons had combined in the genesis of the first atom of hydrogen. [...] Words of power and majesty that could pluck a quark from the heart of a neutron or rend a quasar asunder. They were words written in a different universe: the cosmos that had existed before the present one, the universe whose death knell had been the birth screams of the here and now. The universe that the Doctor had spoken of to Anne Travers when he had described the origins of the Great Intelligence.
The most powerful tool developed by the Time Lords was block transfer computation, the ultimate expression of mathematics. With it, one could manipulate matter and energy, time and space, and fold dimensions like so much origami. [...] Quantum mnemonics, the dark science of an earlier race of Time Lords, made block transfer computation seem like a conjuring trick. With just a few words, a practitioner of their great art could grasp the basic nature of reality around the throat and shake it into a new configuration. A bon mot of quantum mnemonics could bring about a premature death, or a run of good luck. A sentence could transform a planet's history and destiny, changing a world of barbaric war into an elysium. And a carefully constructed paragraph could rewrite the entire universe. Or destroy it utterly.

It's strongly implied The Staff (a Time Lord weapon) from Parliament of Rats pulled a white hole from the previous universe and was going to make it 'real'; the writer of this story is a Faction Paradox writer, the staff was only on Lethe because of a conflict that occurred in a Faction Paradox story, and the term 'old time' is used in reference to the pre-Anchoring universe.

No, lord. Lords, like yourself, did great things on this rock but they are now gone to dust. Such is our destiny. Oh, lord, it is wonderful to touch the clean purity of your DNA. These human creatures smell. Their flesh stinks. They are not like us. [...] I structure. I rationalise. I find weaknesses in the fabric and bind them tight. And they confound me. They use us to pursue crusades of superstition. We did not do that.
Yes, there's no need to shout. This 'White God' is of your creation? We were made to draw it from the structure. It is a living thing, a white hole, from the old times, when such things were allowed. We can barely control it. It stands on the threshold of the event horizon and will become too real soon. Give us orders and we will push it back into the shadowlands, where it will not exist.

“Doesn't surprise me,” said Chris. “It's a pretty obscure legend based on a few, disparate facts. The story goes that just before the Great Houses tamed the chaos of the 'old times' with their laws, they had last minute doubts. What if they'd missed something? What if, once they introduced their checks and balances, that causality didn't behave in the way they had predicted? - Weapons Grade Snake Oil

The previous universe was utterly irrational, existing with infinite possibilities ('flavours of reality') and no laws of physics.

There was a city, buildings carved into gigantic tusks of ivory that sprouted from the ground and formed arches a mile high, great arcs laced with crystalline clouds. The streets were made of cobweb, glittering pathways spun by mechanical spiders, and between them hung enchanted gardens tended by men of stone. Down on the ground walked the skeletons of mammoths, their ribcages stuffed with steam-powered engines, scholars and philosophers riding on their backs. Chris had seen enough in his travels to know that a great many unlikely things were possible. Aliens could look like pixies, bio-machines could be made to resemble dragons, cities could be built out of sound... but there were things in this place he couldn’t even name, things he had no experience of, that seemed at odds with even the most exotic of alien technologies. Things that were impossible. Yeah. Impossible. Things even the Doctor couldn’t have shown him. He was seeing it all in the face of the Carnival Queen. – Once upon a time, she said, this was your universe. Long before your time, before any time that you could measure. A place of endless miracles, non? No harsh sciences here, no mundane little laws of physics, no guiding principles. There was just possibility. An infinity of possibility. Now. Look. Chris wasn’t watching the city any more. There was a different world etched into the Carnival Queen’s expression now, a world inhabited by people; people he could recognize as people, not monsters or automatons. The cities were just as large, but there were less of the impossible things. The planet looked... well, reasonable. Sort of. – This was the world of the Watchmakers, Christopher. One of the first Great Races. Things of extraordinary power. Perhaps more power than they ever realized. See?
And were there monsters here, crawling out of the blackness? No, perhaps not; there were only possibilities, and you could see anything amongst the possibilities, if you looked hard enough. Sometimes, the things she saw (or thought she saw) broke the laws of nature, or the laws of physics, or the laws of time, or laws there weren’t even names for. Whenever she caught a glimpse of something impossible, her spine would burn and she’d spasm like a dying animal. ‘But there are infinite worlds in this realm, Marielle. Why choose one at all? Why tie yourself down to a single flavour of reality? Why not live with the possibility of all of them?’ Duquesne shook her head. ‘We all need something to hold onto, Horloge. We cannot live our lives in the dark.’
‘No,’ said Christopher Cwej. The Carnival Queen looked surprised, and the look revealed entire lifetimes of experience. ‘No,’ Chris said again. ‘I don’t swallow it. What you told me doesn’t make sense. How could anyone just reach into themselves and pull out their irrational bits? I mean, let alone a whole species...’ – Is there a problem, Christopher? ‘It doesn’t make sense! Magic and everything. It’s not real. It’s just superstition.’ That’s what the Doctor said, anyway, he thought. But he didn’t say it. – Superstition. The Carnival Queen laughed. – Haven’t you ever wished that someone would call you, and believed that it was your doing when they did? Haven’t you ever crossed your fingers for good luck? Or believed, just for a moment, that when you cheered on your favourite sub-quantum-para-football team, your wish was what made them score the winning goal?

As testament to this fact, the culmination of irrationality spawned a billion new universes.

– I’m the one who starts the carnivals, Christopher Cwej. The one who makes the music that plays when civilizations fall. Sister to superstitions, grandmother of gynoids. The spirit imprisoned in every piece of clockwork. Matheson Catcher would call me the enemy of all humanity, which seems funny, when you consider how long he’s been under my spell. There was a moment’s pause, and in that moment a billion possible new universes were born. – Call me Cacophony. Call me the Carnival Queen. And I’m very, very happy that Marielle has let me back into the rational universe.

However, the Time Lords removed irrationality from the universe and invented rules and structure (the 'Anchoring of the Thread').

The Watchmakers. Logical, masculine creatures. They rejected the possibility, and denied the world of wonders. Perhaps it scared them. They wanted existence to be precise, to be mechanical, so that they could live their lives to a solemn timetable. They wanted to understand the universe in the same way you might understand a piece of clockwork. As a cold machine. No room for cities of brass or dragonfly-gods. They invented rules, and tied creation down to those rules.
– Nobody is entirely rational, Christopher. Not even the Watchmakers. They wanted a universe of Reason, but to get it, they had to give something up. Those little irrational parts of themselves. Those small corners of their souls that believed in the superstitions, that wanted the world of wonders back. The mutable parts. The changeable parts. Across the Watchmaker world, the people were grasping their irrational shadows and hurling them away. The shadows shrieked into the sky, screaming, crying. Forsaken. They congregated in the upper atmosphere, becoming one great cloud of unreason. 'Go,' said the King. And the cloud went. It shrieked across the skies, exiled from its homeworld. It screamed through galaxies, unwanted and alone, until the rational universe opened up and it vanished into the darkness on the other side of existence. 'There,' said the Watchmaker King. 'Now We Are Things of Reason Absolute. Our... Demons... Are Safely Confined, Beyond The Reach Of Man Or Machine. We Are Perfect. We Are Whole.'

The early universe was effectively structureless, but the Great Houses seem to have known that this state of affairs wouldn’t last. Given enough time it would inevitably begin to develop a definite framework, as new cultures emerged across the span of the continuum and new species began to impose their own versions of meaning on the continuual strata. The ever-nervous academicians of the Homeworld knew they wouldn’t be alone much longer, and most likely feared how other intelligences might influence the shape of the future: in theory the coming generations of species could be so different that a collision between them and the Houses would be as catastrophic as a collision of different forms of matter.
But the Houses’ grand solution was to create the structure of the future for themselves.
The first attack came as a primal manifestation, destroying the site of the machinery and most probably everyone involved in the process, leaving an enormous crater – the caldera – at the centre of the new born version of history. - The Book of the War

For some context, that last statement refers to the Yssgaroth / Great Vampires. Part of the statement is true, but the Time Lords actually unleashed them before the Anchoring of the Thread and covered up this fact.

In particular, Rassilon removed magick, barring a trace of psionics. And returning real magick to a planet will eventually erase it from history.

‘The first to evolve in this universe, yes,’ said the Doctor. [...] ‘Back then we were the Shadow people, caught between the warm dark of magick and the cold light of science. Magick predominated for a long, long time. And then Rassilon made his decision.’ [...] ‘The world solidified around us, like water turning to ice. Squeezing out the magick. But, like an ice cube, there were little cracks and bubbles. Psi was the last magick to survive, perhaps because it was the least impossible, the closest to science. The residue of psi became a network of ley lines, stretching through the universe in improbable directions.' ‘It’s still there.’ Roz said, ‘And Iphigenia is… on one of the ley lines?’ The Doctor nodded. ‘The Time Lords were aware of the leylines before the Wars began. We’d chosen to make the universe rational. Its irrational citizens objected. So we turned the psi lines into weapons. A Distant Early Warning line that stretched through the galaxy, studded with receivers the size of mountains or even small moons, parabolic dishes disguised as craters. Listening for eruptions of psi power beyond Gallifrey.’ - So Vile a Sin

Anhedra, a tiny ballet dancer with glorious limbs and a nasty smile, has spread her arms to weave gleefully through a vast craton of slow–cooking diamonds. She shrugs. ‘Then we will turn him from science to magic and Tagonique will be saved from the Enemy.’
Granted power by the Observer Effect of Mesquividas's fall, they invade the minds of the Tagoniqui, draw out their magical worldview, infect the substrata with it, punch backwards through time to link with the moment in which the universe became one thing or another, and with a concussion which blazes, at temporal frequencies, like a quasar, they smash the probability wave in the wrong direction and funnel the consequences forward through time to Tagonique. Real magic comes to Tagonique. The Tagoniqui are liberated from the Enemy. In seventy–three years and four days they will all cease to exist. Night falls. In Mesquividas's tower, all is quiet. The wheels of the machine are still. But outside, the stars turn in their ancient round towards dawn. The moon is setting. Tagonique revolves towards spring. The hidden sun moves in stately spirals about the galactic centre and the great wheel of the galaxy rolls on. Beyond it all, congruent with all other circles, the War encompasses all. Wheels within wheels within wheels, turning towards eternity. - A Romance In Twelve Parts: Alchemy

The characters speculate that astrology is basically a remnant of the laws of physics from the universe predating the Big Bang.

MR SMITH: The origins of astrology are lost in the mists of time.
LUKE: It says in here that the earliest record of astrology was in Babylon, in the sixteenth century BC.
MR SMITH: It is older than that, not just here on Earth. Primitive cultures across the universe charted the patterns of the stars. This is the zodiac of the planet Ventiplex, for example. And this is the zodiac of Draconia.
LUKE: There's astrology in the cultures of other planets?
MR SMITH: Yes, Luke. A similar system operates in the culture of almost every inhabited planet.
LUKE: So it's everywhere.

RANI: Like Clyde said, how can we detect something we don't believe in? The power of the Ancient Lights. What if it is astrology? What if astrology is true?
SARAH JANE: It can't be true.
LUKE: It's completely contrary to the laws of physics.

RANI: Hang on. Astrology breaks the laws of physics.
LUKE: What are you getting at?
RANI: Well, what if the Ancient Lights come from somewhere else? A place where the laws of physics are different, so they can break ours?
LUKE: That's like saying you could break the law of gravity.
RANI: But maybe that's why Mister Smith said nothing burnt my jacket. What if this energy the Ancient Lights use is a different kind of energy to anything we know?
SARAH JANE: No, Rani. The laws of physics, they're are the same across the universe.
LUKE: Our universe. But what if the Ancient Lights are from another one?

LUKE: Mister Smith said every galaxy has its own form of astrology, not just Earth. What if astrology is a kind of memory of a time before? [...] Thirteen billion years ago, the universe was created. A massive explosion, the Big Bang. But what was there before?
SARAH JANE: Nobody knows.
LUKE: What if there was another universe?
RANI: Where the physics were different. Where astrology worked.
SARAH JANE: And this energy somehow survived the Big Bang.
RANI: The Ancient Lights. So they're very ancient. What have they done the last thirteen billion years?
SARAH JANE: And why have they picked Trueman?
MR SMITH: May I make a suggestion?
SARAH JANE: Go ahead, Mister Smith.
MR SMITH: If Luke's theory is correct, the energy form has been waiting for exactly the right astrological conditions across the universe. Trueman's birth chart is a vital part of that equation. He is the channel the energy needs.

The story strongly supports their speculation.

TRUEMAN: I have a message for the world. Don't be afraid. Something wonderful is happening. Very soon, every star in the entire universe will be aligned in a perfect conjunction for the first time in thirteen billion years. The way is clear. The Ancient Lights will shine again.

LUKE: I wasn't born. I have no birthday, no star sign, so astrology doesn't work on me. The circle was like an electrical circuit. I broke it.

For context, Dharmayuddha was written by Aditya Bidikar, an Indian writer. It's a kind of contextualisation of Mahabharata (a mythologised account of the semi-apocryphal Kurukshetra War) in the Faction Paradox/Doctor Who universe.

Kaliyuga, the age of darkness, ignorance and sin, is the current state of the war-torn great kingdoms. It 'proceeded' comparatively prosperous Dvapara Yuga.

Magadha – which is one of what they call Mahajanapadas, or ‘great countries’ – is among the bigger kingdoms in what will one day become India. In the Kaliyuga, which is where you’re sitting, it will be ruled by the conqueror Bimbisara and his supposedly indomitable son Ajatashatru. Then there will be this one time when King Alexander’s armies will mutiny at its borders and demand to return home. And later, Chandragupta Maurya will pass Magadha on through the generations to King Ashoka, who will gain the nickname ‘Ashoka the Cruel’ for his less peachy qualities, and who will then convert to Buddhism and be instrumental in its spread throughout Asia. But in the time we’re talking about – in the Dvapara Yuga – Magadha is ruled by the legendary Jarasandha. And it has enjoyed a long run of peace and serenity while Jarasandha’s armies march around Bharata cowing other kings into submission. Today, however, marks a lull in Magadha’s battle-mongering, as religious occasions tend to do.

In truth, Kaliyuga totally replaced Dvapara Yuga.

And then, nine months later, each of them bore half a son, dead. What had happened was that the fruit contained an aatma – the essence of everything you are, have been and will be – and the aatma had been split into two. The two half-sons, horrific to look upon, dead, but still shifting and fragmenting along their broken timelines, were thrown out into the forest near Magadha. And there… Hang on. Let’s take a moment here. You know about aatmas and fractured timelines, right? Well, perhaps an explanation is in order. See, you live in the Kaliyuga, the Dark Age. You think of time in a linear fashion – in terms of before and after as though that actually refers to time itself. You can’t help it. You think your yuga follows the previous yuga, when it actually replaces it. Your minds, which can only bend so much and not a whit more, have simplified the entire story of the yuga before yours to fit in with your little linear outlook. You think of devas and asuras as gods and monsters, and of the divine human as fantasy. But the truth is stranger than your mythology. Dvapara Yuga falls to Kaliyuga, and gives rise to your puny race, but before this occurs, there’s a great war in time, called the Kurukshetra war. The Kurukshetra – ‘the land of Kuru’ – is a piece of the Bharata continuum, the continuum that you live in, but before history is rewritten to suit the gods.
She travelled the fractured timeline of the Dvapara Yuga, and one fine day, she found a peculiar delight – a grotesque dead baby with its existence split neatly down the middle. She was about to eat it, of course, but then she noticed that each of the halves was reaching out to non-existent timelines to complete themselves. To fatten the meat, she helped them, joining the two halves together into a whole child with two biodatas with bits borrowed from two non-existent universes. The child came alive. Jara, enchanted by the child, couldn’t bring herself to kill it. So she took it to the closest kingdom – Magadha – and gave it to the king. Brihadratha recognised his son, so he took him back and named him Jarasandha in honour of the creature that had brought him back to life. So that’s the truth behind the story that you might know. But even this story had a problem. It skipped the happily-ever-after – although we might presume Brihadratha got one – and had far-ranging consequences. Jarasandha lived one life, but he also remembered two others. As he grew up, he started to get flashes of events as they might have transpired if his choices had been different. With penance and meditation, he expanded his view from himself to the entire world; and from the past to the present and the future. The memories of the two alien timelines he was torn from coalesced into a picture of futures that had already happened, but which could perhaps be averted. He saw the entire story of the Dharmayuddha from on high, and he saw that in each of the impossible universes – no more impossible than his own – a child was born, supposedly the seventh incarnation of the god Vishnu.

Humans possess insane abilities in the Dvapara Yuga.

Cousin will turn against cousin, five Pandavas waging war on one hundred Kauravas. Arjuna, currently sitting in a tent in Jarasandha’s garden – thousand armed Arjuna, compressing time to move faster than you can think possible, looses fiery arrows of possibility at his enemies. Wherever the arrows hit, time loops trap enemy soldiers in unending moments of futility. Infinite timelines crash into men’s heads, weapons age Arjuna’s enemies into dust. Some let potential timelines loose, causing chain reactions that infect soldiers and fracture their souls. Arjuna’s brother Bhima the simple-minded, now gorging on laddoos, his favourite sweetmeat, will carry his mace and destroy timelines, creating widows that were never married, children born to fathers who didn’t exist. Their elder brother, Yudhisthira the truth-teller, whose very words can collapse impossibilities into truth, concocts stories about how the brave but naïve Pandavas were cheated out of their kingdom, making this into immutable fact. His youngest brothers Nakula and Sahadeva, two iterations of the same person, lead their twin armies of imaginary animals on towards the Kauravas. Strange hybrid creatures made of broken time tear into the Kauravas; the skies themselves go black for the fall of Jayadratha. The Kauravas operate the chakravyuha – a whirlpool created of holding patterns of soldiers – which sucks people in and leaves them stranded in the void between worlds. Arjuna, his son Abhimanyu lost in the vortex, kills his teacher Dronacharya and the immortal Bheeshma. Jarasandha sees that the Pandavas and Kauravas will be fighting a war already lost by both. He knows that the gods are watching, waiting for the Dvapara timeline to weaken, so they can deploy their weapon.

Due to the manipulation of the gods (the Time Lords), the universe was replaced and bound to a single thread, where humans were created in the image of gods rather than being gods.

The arrow piercing Krishna, and Krishna exploding – a universe within a bomb, contained by a god inside a man – and Kaliyuga unleashed, wiping out the Dvapara Yuga and installing itself in its wake, like a new operating system. Binding the universe with a new thread, one wherein humans were no longer as gods, where the gods made humanity in an abortion of their image. He knew that for the Dvapara Yuga to endure, the scene on the battlefield had to be prevented.

In The Infinity Doctor, an old Gallifreyan proverb is that time runs in circles.

‘Time moves in circles,’ the President noted. It was an old Gallifreyan proverb, one that was literally and metaphorically true.

Reality is a slate, and so much is unwritten or simply sketched in that reality exists as pages of palimpsest universes.

‘As he fell, he tore a hole in time, like a fingernail down a blackboard. It was as if a hole had been ripped from the page of a book. I saw the pages behind ours, other times and spaces. Not parallel universes, but palimpsest universes. Reality is a slate, and history and memory and matter and time are just patterns of chalk on that reality. There is so much left unwritten, or just sketched in. A casual word, a glance down the wrong alleyway and… and everything could change. The Time Lords hold such power, the power to destroy a planet or change a young girl’s past. We devour time as a beetle chews up leaves or bacteria rots a corpse. That power scares me. Nothing is safe, nothing is sacred.'
The Doctor hesitated. He’d not said ‘thirty‐five’, he’d said a different word, and then before that, they’d said it, so he’d said a different number, so they’d said it. It was an endless sequence, like trying to name the biggest number, or working out whether the chicken came before the egg. He could understand what was happening, but the answer remained just one step out of reach. It was a simple question with an infinite answer. 'The past is as malleable as the future. We see the future, we do not affect it. It might seem paradoxical to you, but as a time traveller you must understand something of the complex nature of the universe. There have been occasions on your travels when you have seen the past unfurling around you, just as you remember reading would happen. Time is relative.’ ‘The observed past does not change,’ the Doctor objected. ‘That is one of the fundamentals of time theory.’ ‘You have free will,’ Willhuff assured him, ‘in the past, the present and future. Nothing is fixed, nothing that can be remembered can’t be forgotten.’ ‘But how can you say that I’ve got free will when you know what my actions will be?’ ‘We will stop you.’
The Doctor sighed. ‘That’s what we’ve created – a universe where everything is nothing. A universe where nothing matters. Of course you can rewrite history, but you shouldn’t. As long as you have these great powers, nothing is real.’

For example, Omega has witnessed repeated versions of Gallifrey.

The Doctor took another step up, looked Omega in the eye. ‘You’re a Gallifreyan, Omega. You’re more than that. You must have been hit by the time energies when Qqaba went nova. You must have taken the full force of the explosion. My bet is that you understand Time a great deal better than your average Time Lord.’ Omega laughed, the sound originating all around the room. ‘You may be right.’ ‘And existing outside your native universe must also have given you – what was your phrase? – a “unique perspective”.’ The red eyes narrowed. ‘I have seen the past and future change. I have seen a universe where there was no Rassilon, and the Time Lords were gods thanks to me. I have seen a universe where Rassilon still rules Gallifrey from deep within the Matrix. Another where he was a woman, and my lover.’ ‘Parallel universes?’ ‘Such places exist, but this was our universe, riddled with paradox and contradiction likes weevils in a biscuit.’ The Doctor drew back a little. ‘I know a number of seafarers who prefer their biscuits with weevils. It adds to the taste, and weevils are a very good source of protein, or so I’m told.’ Omega was ignoring him. ‘In all of those realities, in every version of history I am trapped here. Sometimes by treachery, sometimes by design, once even through choice. There are an infinity of choices, an infinite number of Doctors. Yet I am all the Omegas, I am the only one.’ ‘So you’ve searched all those different realities looking for a way to escape, and never found the answer?’

In Mr Saldaamir, it's stated that the original universe was a simple, elegant parabola. Nothing could surpass the speed of light or travel through the immutable note of time.

The original idea was very, very simple. You had a timeline. Year three followed year two, followed year one. If you could count, you could understand time. Seconds ticked by, one after the other, everything travelling in the same direction, nothing going faster than the speed of light.
Once upon a time. Unlike small children, the elder laces were in no rush. They were, on the whole, immortal — living a long time being, of course, being one of the prerequisites for being an elder race in the first place. And, time being a very simple concept to grasp, most of them could see the future, in the same way that if you can count to ten you can count to a trillion, if you have the inclination. The universe was an elegant, beautiful, place back then. A single, harmonious note. It has a golden age. Really it was. For the first few billion years, nothing was wrong and nothing ever went wrong. Even the bad things that happened were good — that's to say they happened for a good reason, and lessons were learned. It wasn't stagnant, either. Nothing was ever dull. It was an age of heroism, of exploration, of discovery. Above all else, it was a time ol progress. That's what time did, then. Progressed. Everything progressed, everything got better with age. Giants walked the earth, standing on the shoulders of giants. Literally, sometimes, if the mood took them. It was the golden age that all the legends describe, that all the politicians hark back to, the one that you vaguely remember yourself, back when things were simple and sunny.

However, the Time Lords reduced the Golden Age to a squiggle, where subjective timelines and branches are the norm.

Very early on, mathematicians, philosophers, physicists, fantasists and who knows who else all realised that, theoretically, it was possible to travel in time. The physicists even jokingly pointed out that if you managed to — hee hee — find (or create) a very specific type of supermassive black hole — snicker — one that had a singularity that was exactly the right shape, and — hoho — somehow managed to get it spinning in a certain way and a— fnarr fnarr — bent a couple of spare dimensions around a bit until they faced the other way, then somehow — oh, you're killing me — developed a forcefield that would stop you from instantly being annihilated by all the anti-matter, radiation and raw temporal forces, then — it's a cracker — managed to find a way to both access the singularity and keep the event horizon, then finally — stop me if you've heard this one — you could harness the resultant energy to create a working time machine.
And, then, that evening, suddenly the timeline stopped being an elegant parabola. Now it was a squiggle. With branches off and crossing out and gaps and hits which repeated each other, or cancelled each other out. Suddenly nothing made sense, except on a very, very local level. You'd think, what with being able to see the future, that the elder races or the universe would have seen it coming. They did, of course, they'd just got the order wrong. They'd assumed that five o'clock would follow four o'clock, that six o'clock would show up soon after five, and that — crucially — this would hold true for everyone.
Within a generation, it had all settled down again. The golden age was over, what with the hordes of ancient evils trying to drain the life from whole planets and all, but it was clear that an uncertain future and a squiggling, subjective timeline was “it” from now on.

This also had the side effect of creating evil creatures, like the Celestial Toymaker.

The next six days were, it's fair to say, pretty traumatic for all concerned. The elder races tended to do four things. 1. Go mad. 2. Leave. 3. Get killed. 4. Regress. Some did all four. Some only managed one of the above. It was one of those times where people tried new ideas. One chap dressed as a Chinese mandarin and became obsessed with toys and games. Some went into hiding, or left the universe altogether. A couple of groups decided to swarm across the universe destroying all life. Because, suddenly, anything went and everything was up for grabs. Within a generation, it had all settled down again. The golden age was over, what with the hordes of ancient evils trying to drain the life from whole planets and all, but it was clear that an uncertain future and a squiggling, subjective timeline was “it” from now on. What was also clear was that Time had been invalided out, and needed someone to look after it.

N-Space

The Ocean of Time

The first law of time forbids anything from traversing along its own subjective time stream (meaning the string of events that it personally experienced), and it's actually very difficult to perform outside of disruptions to time or certain points in the flow of history.

First and foremost, he established the Laws of Time. Perhaps ‘established’ is too strong – he was largely just describing a set of scientific principles akin to the Laws of Physics. The unintended consequence of laying down the law in this way, of course, was that it tempted so many others to break it. He said ‘must not’ when he meant ‘cannot’, although a deeper understanding than he then had might have led him to ‘can, but Time will (usually) reassert itself’. Anyway, he laid down the five great principles that have been taught to every Time Lord from childhood ever since. - A Brief History of the Time Lords

PROTOCOLS OF LINEARITY [Great Houses: Culture] Of all the Protocols whichdefine the limits of the Great Houses, the most widely-discussed are theProtocols of Linearity. Though the Houses have almost complete freedom ofmovement in the Spiral Politic, the one major exception is the Homeworlditself. Not only is it impossible/illegal to travel into the Houses’ own past, but it’s built into the very nature of the Homeworld’s time technology that whenever Homeworld-time meets outside-time, the two should become analogous.
In effectwhat this Protocol suggests is that whenever an agent enters an area oftime outside the Homeworld, the area becomes in some way “linked” to theHomeworld. Even though the two worlds may be aeons apart, events on thoseworlds appear to take place simultaneously.
NAPOLEONIC ERA [Lesser Species: Event (Earth, C18-19)] The Protocols of Linearity state that whenever one of the time-active powers makes contact with one of the lesser species, a temporary link will be forged between their relative histories so that the “present” of the power and the “present” of the species will be briefly indistinguishable even though their cultures may be separated by billions of years. - The Book of the War

CHANCELLOR: You can't allow him to cross his own time stream. Apart from the enormous energy it would need, the First Law of Time expressly forbids him to meet his other selves.

DOCTOR: What about the First Law of Time?
DOCTOR 2: Perhaps I could explain?
DOCTOR: Perhaps you could.
DOCTOR 2: Well, our fellow Time Lords out there are just as much under siege as we are.
DOCTOR: What?
DOCTOR 2: And they couldn't send anyone to help you. But they did summon up enough temporal energy to lift me out of my bit of our time stream and pop me down here, into my own future, so to speak.

This doesn't refer to a character travelling backwards or forwards through time, but through its very own flow of time. For example, if your pet died, travelling back in time to save your own pet would contravene your own established history since the pet's death is part of it. It's also why The Doctor doesn't just interfere with deaths that have already happened every time a companion dies.

TEGAN: Oh, great. You make it sound like a shopping list, ticking off things as you go. Aren't you forgetting something rather important? Adric is dead.
NYSSA: Tegan, please.
DOCTOR: We feel his loss as well.
TEGAN: Well, you could do more than grieve. You could go back.
NYSSA: Could you?
DOCTOR: No.
NYSSA: But surely the Tardis is quite capable of-
TEGAN: We can change what happened if we materialise before Adric was killed.
DOCTOR: And change your own history?
TEGAN: Look, the freighter could still crash into Earth. That doesn't have to be changed. Only Adric doesn't have to be on board.
DOCTOR: Now listen to me, both of you. There are some rules that cannot be broken even with the Tardis. Don't ever ask me to do anything like that again. You must accept that Adric is dead. His life wasn't wasted. He died trying to save others, just like his brother, Varsh. You know, Adric had a choice. This is the way he wanted it. - Time-Flight

Also, when a character uses the term 'timelines', they aren't simply referring to the what-ifs / could-have-beens or alternate universes in many circumstances. Time in Doctor Who runs along different tracks and isn't always precise.

When distance is achieved, the patterns run and straighten. It becomes possible to see, linked by lines of deeper or lighter probability, the tracks of the immediate past and future: the mainlines of eternity, the central thoroughfares of history, the abandoned and boarded-up stopping places of the soul. - The Brakespeare Voyage

So often times characters will say timelines, when 'timeline' would suffice in other works of fiction.

DOCTOR: Sent a message through the timelines into the Vortex, cos I know they're in there, like sharks in water. Always scoping, always ready. - Revolution of the Daleks

MASTER: Weird, how you don't remember any of this.
MISSY: The two of us together puts the timelines out of sync. You can't retain your memories, so I don't have them. - The Doctor Falls

As an example of how time tracks relate to linearity, Tenth Doctor accidentally jumped a time track and fell into a Dalek that was part of his relative past.

‘Oh, it’s not space I’m worried about,’ said the Doctor, lost in thought. ‘The TARDIS seems to have slipped a time track… I’ve travelled back in the Daleks’ own timeline to way back when.’
‘Well, nothing really. It’s just a bit of a coincidence, when you think about it. Coming here, looking for some sort of temporal disturbance – and when I’ve already jumped a time track to a period in history when…’ - Prisoners of the Daleks

Dalek and Time Lord histories had become linear at this point, as they tried to erase each other from time and essentially locked their established histories. Similarly, Compassion (a humanoid TARDIS) couldn't escape an event that affected space-time in her timeline by travelling back through time.

The timeline of the planet was bent now, wrapped around the Attractor, so that from twelve million AD to sixty billion there was no normal history, not even that of humanity’s long stays on Mars, and Pluto, and finally as bio-formed living light within the solar photosphere itself. Instead, everyday was bent at an angle to time from which the point of no-return, the dreadful black and yawning maw of the attractor could be seen as if it were no more than ten light years away. [...] Frantic, Compassion accelerated back. Her personal time was caught up in this event, bound to its linearity, if she merely followed her own track back, the dissolution would keep pace with her day by day, second by second – she would never find the intact human world on which she could make her stand. She would never learn who was responsible for they would always be finishing just as she arrived. That thought was intolerable. She drove herself harder still. It was not impossible - although it was in many senses forbidden - for her to outstrip the wave of change working back along the history of man. She might – if she strained every energy - leap from one turn of the skein and whorl of time to another earlier strand. A process the first pioneers among the time-ships had termed ‘skipping a time track’ as if creation were a gramophone record, and a time-ship a silver needle. Doing so, she might find an age which had not ‘yet’ been pulled in to the process – even though if she waited and reached it in its due course she would find it devoured at her moment of arrival as all the rest had been. - The Brakespeare Voyage

Maybe the most prominent example is The Woman in the Fireplace. The Tenth Doctor was unable to violate the order in which he'd met Reinette.

DOCTOR: They teleported. You saw them. As long as the ship and the ballroom are linked, their short range teleports will do the trick.
ROSE: Well, we'll go in the Tardis!
DOCTOR: We can't use the Tardis. We're part of events now.
MICKEY: Well, can't we just smash through?
DOCTOR: Hyperplex this side, plate glass the other. We need a truck.

Comparatively, he was able to visit Rose before they first met because she didn't know it was The Doctor, and this occurred much further into The Doctor's subjective timeline than his eighth regeneration. So historical facts weren't violated, just altered and added to.

An event that is immutable, unchangeable, etc in the established history of the universe is referred to as a fixed point in time.

FIXED POINT: Historical documents make the claim that, during the strike on the displaced Earth in the 21st century, the Daleks spared the life of space pioneer Adelaide Brooke (fig 11.06). Despite the fact that they were engaged in a campaign that would, if successful, destroy the entire universe, the Daleks understood that Brooke was a pivotal figure in the established history of the universe. It has been speculated that the Daleks did not kill her as it may have had a follow-on effect that would have derailed their own doomsday plans. - Dalek Combat Training Manual

In particular, the eruption of Mount Vesuvius and fall of Pompeii is a fixed point.

DOCTOR: Not this time. Pompeii is a fixed point in history. What happens, happens. There is no stopping it.

DOCTOR: Some things are fixed, some things are in flux. Pompeii is fixed. - The Fires of Pompeii

The bulk of fixed points are created either naturally, or by learning about an event before it actually occurs (i.e, in The Angels Take Manhattan, River broke her hand by escaping a Weeping Angel's grip because she read a book from the future that said it'd happen). Daybreak and The Vardan Invasion of Mirth explain that probability waveforms collapse from infinity to one.

This means that fixed events can be sabotaged before they exist under the right circumstances, or even manipulated to achieve a certain outcome (i.e, The Doctor survived his apparent death at Lake Silencio by making it appear that he died, thus keeping the flow of established history intact).

I'll elaborate on the effects of actually breaking an established fixed event below, but, as an example of how dangerous it is, breaking the established history of Captain Jack (a fixed point, in and of himself) in The Death of Captain Jack created an entire version of the universe that was negated upon his death.

In Vortex Butterflies, it's explained that N-Space is a space-time continuum that appears as one enormous moment to time-sensitives. Most of this 'ocean' is composed of flux potentialities that orbit fixed events.

DOCTOR: Some things are fixed, some things are in flux. Pompeii is fixed.
DONNA: How do you know which is which?
DOCTOR: Because that's how I see the universe. Every waking second, I can see what is, what was, what could be, what must not. That's the burden of a Time Lord, Donna. And I'm the only one left. - The Fires of Pompeii

ROSE: I can see everything. All that is, all that was, all that ever could be.
DOCTOR: That's what I see. All the time. And doesn't it drive you mad? - The Parting of the Ways

REXX: The deal is that someone engineered this. That black hole up there shouldn't exist at all, not in this sector of space and certainly not at this point in time. Even as a potential aspect of established history its presence here is more than a little... disruptive. As you can hear reality is wearing thin, timelines are crashing into one another.
ACE: Those voices...
REXX: It must be so hard for you, not being a Time Lord. We're so used to these phenomena, we experience every second every moment every alternative of every instance all at once, but you... you've never had that. Sometimes we forget that you're still learning. - Intervention Earth

They are the 'flow' of time, while the fixed points are the important events. These flux events are connected to the creation of alternate universes, as an Osirian Quantum Harvester in Spiral Staircase could see alternate timelines and parallel universes because she was connected to flux events.

I will expand on this point later (see N-Space's Vortex - Size).

Since history is in flux, humanity could be destroyed by an event in its past that also involves its future.

MARTHA: The thing is, though am I missing something here? The world didn't end in 1599. It just didn't. Look at me. I'm living proof.
DOCTOR: Oh, how to explain the mechanics of the infinite temporal flux? I know. Back to the Future. It's like Back to the Future.
MARTHA: The film?
DOCTOR: No, the novelisation. Yes, the film. Marty McFly goes back and changes history.
MARTHA: And he starts fading away. Oh my God, am I going to fade?
DOCTOR: You and the entire future of the human race. It ends right now in 1599 if we don't stop it. But which house? - The Shakespeare Code

And this isn't limited to the post-Time War universe. In Doom Coalition: Songs of Love, Liv Chenka (who's from the 30th/31st century) and Helen Sinclair are stranded in the 25th century as the Doom Coalition are destroying the universe. Liv has to explain that history is in flux, so being from the future doesn't guarantee that future.

DOCTOR: No. That's the world as Sutekh would leave it. A desolate planet circling a dead sun.
SARAH: It can't be! I'm from 1980.
DOCTOR: Every point in time has its alternative, Sarah. You've looked into alternative time.
LAURENCE: Fascinating. Do you mean the future can be chosen, Doctor?
DOCTOR: Not chosen, shaped. The actions of the present fashion the future.
LAURENCE: So a man can change the course of history?
DOCTOR: To a small extent. It takes a being of Sutekh's almost limitless power to destroy the future. Well? - Pyramids of Mars

DOCTOR: Just before you did. Look, I know what you're thinking, but it's one possible future. It's one timeline. You want me to tell you that Earth's going to be okay? Cos I can't. In your time, humanity is busy arguing over the washing-up while the house burns down. Unless people face facts and change, catastrophe is coming. But it's not decided. You know that. The future is not fixed. It depends on billions of decisions, and actions, and people stepping up. Humans. I think you forget how powerful you are. Lives change worlds. People can save planets, or wreck them. That's the choice. Be the best of humanity. Or... - Orphan 55

If it wasn't obvious enough, flux events exist alongside other flux events. They don't just pop into existence along the continuum.

‘Have I seen them? Yes, I’ve seen them. Or heard of them. Englands with a third, fourth, or fifth Civil War. A resurgent monarch who ruthlessly oppresses all democracy. Or a triumphalist, hereditary Puritan Protectorate that rules the country until the twentieth century. Or an invading Catholic army which takes advantage of England’s crisis to take over most of the known world. Oh yes, they’re all out there. All kinds of futures. Some great, some truly terrible.’ - The Roundheads

So how is true history decided if it's so subjective?

To explain what established history is, we'll first need to go over the Anchoring of the Thread (just the basics, though).

The first introduction to the Anchoring of the Thread was actually a somewhat mythologised (but accurate) account from The Deadly Assassin, which states that the Eye of Harmony balances all things so that they may neither flux nor wither, nor change state.

WOMAN: Now Rassilon found the Eye of Harmony, which balances all things, that they may neither flux nor wither nor change their state in any measure. And he caused the Eye to be brought to the world of Gallifrey wherein he sealed this beneficence with the Great Key.

In Neverland, it's stated the Time Lords locked and anchored the continuity of the universe and the Vortex, creating a chronology across all of positive time, which is hitched by the Eye of Harmony and doesn't flux or wither. This is referred to as The Web of Time—the engineered, memetic structure of history.

RASSILON: A long time past, I helped end centuries of tyranny and bloodshed on my own planet. Helped to usher in a great age of enlightenment, with faithful counsel from the wisest of my Technomagi. I locked the space time continuum with the great Eye of Harmony. But, in my declining years, I grew fearful that by constructing the one true Time, I might have brought into being its very opposite. The menace of what I termed anti-time. A vile poison which might yet spill out to contaminate and undo all I had sought to achieve filled me with horror and dread. I resolved to journey into the strange, uncharted fringes of space time in search of my nemesis. And here, in this weird unreality, I found the Neverworld of Zagreus, the corpus of chaos and nowhen. I have battled this entity. It is dormant, docile now. My Tardis shattered, my exit hole shut. I am trapped in this place. But I leave this message in the hope that one day my Time Lords will find a way to rescue me. My body I have placed in a Zero Cabinet nearby, my last breath suspended. If I live, my children, I should like you to revive me and take me to Gallifrey. Take me home.

DOCTOR: Now, how does it go? The Web of Time could not exist until the great Rassilon built the Eye of Harmony, the hitching post of chronology, that which does not flux nor wither nor change its state.
ROMANA: The Eye of Harmony created a universe of positive time, finite time. Gallifrey anchored the continuity of the universe. But just as matter has its counterpart in anti-matter, just as every action has an equal and opposite reaction, then, by all the immutable laws of the universe, positive time, the Web of Time, must have its shadow.

VANSELL: An undertaking which my Agency has been happy to assist. But imagine if the great Rassilon were to be returned to us, he who began the intuitive revelation, who established the Eye of Harmony and anchored the space time vortex. How much could we achieve? How much further could the Time Lords go? Madam President, the proof lies inside a Zero Cabinet somewhere within the bounds of this planet. Or Tardis. Whatever.

DOCTOR: The Web of Time is already stretched at the seams. Gallifrey is the last bastion of positive Time. All that maintains the constance of the universe is Eye of Harmony, and if that is contaminated

It’s long been established that although the universe pre-dates the Houses by several billion years, they were arguably the first to imprint their will on existence, and many of the “natural” laws of creation – the all-pervading Protocols of the Great Houses – were laid down at the start of the bloodlines’ ten-million-year reign during the anchoring of the thread. In effect the Houses built history, engineering it as a complex memetic structure running through the entire length of observed time (though certain parts of the far future seem to be beyond their reach, oddly).
MEME [Terminology] An idea which “evolves” as it passes from one individual to another, and in doing so runs the same risks as any other evolving thing, in that the idea may mutate in order to suit a new cultural environment or become extinct altogether. First coined by western Earth culture in the late twentieth century, the word has become an accepted part of standard English even though many now consider the term to be utterly unnecessary: the argument is that all ideas are by definition memes, and that it’s impossible to conceive of an idea which doesn’t evolve as it’s passed from consciousness to consciousness. (It’s perhaps significant that the word first became popular in the scientific community. In one of his last works R. B. Nevitz pointed out that ‘all artists, visionaries and politicians have an innate understanding that ideas are evolutionary’ and suggested that ‘only someone trained exclusively in the hard sciences, but who had no understanding of the subtleties of culture, could genuinely believe that a special word might be needed for [a] thought which mutates’.) Nevertheless, when War terms are translated into English the word “meme” is often used instead of “idea”, and this is hardly surprising considering the arsenals used in the War. In a conflict where weapons are frequently designed to attack identity rather than solid matter, where tools (and even soldiers) can be manufactured using pen option as a medium… in such a conflict, those involved will inevitably use words which underline the organic, visceral nature of ideas. Quite often the ideas are the enemy, and in many cases will literally have lives of their own, some even possessing the ability to exist outside the context of a living mind. This is certainly true of, say, the anarchitects, and it could be said that the Celestis’ realm of Mictlan is the first major world to be composed of nothing but memes. - The Book of the War

However, it's explained in Intervention Earth that timelines do flux and wither all the time, but history reasserts itself to fit the dominant reality ('established history') set by the Time Lords. As with Ace, Alice Obiefune could feel her own history slipping on Gallifrey (whose continuity is separated from the normal universe, but connected to every aspect of it) in The Lost Dimension.

There was structure, the universe was a web made not of spider’s silk but of space and time. But in such a cosmos, one of fluxing quad-dimensionality, who was to say what was cause and what was effect? Even the newly woven children of his world understood the solution to that solemn inquiry: there was no history, don’t you see, only established history. Time was an ocean of broth, rich in elements and possibilities. Observations could be made to spot trends and to predict, for the oceans of time were subject to the laws of temporal mechanics. - The Gallifrey Chronicles

Established time is named the 'Web of Time' for a reason. The Book of the War espouses that fixed points are node points in history/the foamstructure of space-time that perform essentially the same function as the machinery that locked history to the Eye of Harmony during the Anchoring of the Thread.

The machinery required for the operation ended up comprising the largest structure ever built on the Homeworld. Later accounts describe it as a whole, as one “device”, though it’s doubtful it was designed or constructed that way. The first exploratory vessels, the Houses’ prototimeships, had already begun attaching themselves to strategic points in the formative future. They’d become anchors, holding the structure of history in place, and the machineries erected on the Homeworld could only have been centralised versions of the same technology. But there was a ceremony, without doubt, one great symbolic moment when the mechanisms locked into place and all the fragments of history were connected. Lore holds that elite representatives gathered in the centre of the machineheart to perform the bonding for all their Houses, while field agents in their vessels took their places at the other ends of the “threads”.
The metastructure of history was held together at certain (vulnerable) node points across the Spiral Politic, and it seems reasonable to assume that at these points the foamstructures of the continuum were significantly weakened.

When River Song contradicted an established point, she literally broke time to the point where history existed all at once, causing time to stand still. Even the Time Lords (despite being able to change fixed events in The Time of The Doctor) didn't want to risk fracturing time by saving Clara from a fixed point, with the implication of the story being that the Web of Time was going to unravel.

GENERAL: She's been dead for half the lifetime of the universe. If you tried to change that, you could fracture Time itself. Doctor, Lord President, are you really going to take that risk?

CLARA: They said, your lot, that if you saved me, Time would fracture. What does that mean?

GENERAL: All Matrix prophecies concur that this creature will one day stand in the ruins of Gallifrey. It will unravel the Web of Time and destroy a billion billion hearts to heal its own.

CLARA: Time isn't healing. I am still frozen.
ASHILDR: You know what that means?
CLARA: It means my death is a fixed event. The universe depends on it happening.

However, the Web isn't totally fixed and immutable. For example, if someone who made a minimal historical impact was erased, it'd simply be a tiny hiccup in the Web.

VANSELL: In itself, the Earth girl's survival is not the problem. She was nothing. She would amount to nothing. Her descendants would be nobodies. She's nothing special, Doctor. She wouldn't go on to cure a disease or start a war or discover a planet. By rights, her survival would be but the tiniest hiccup, easily made and easily mended. But her living was a rift. Her very being a breach. Charlotte Pollard is a rip in the fabric of space time, a breach with presence and physicality. - Neverland

LUCIE MILLER: No, listen. She has to be alive, doesn't she? Or else I couldn't have met her in the future, like.
THE DOCTOR: Not necessarily.
LUCIE MILLER: Not necessarily? But I knew her. I know her. She's still knocking around, you know, in Two Thousand and Seven. Good old Aunty Pat. Well, what about that thing you're always going on about? You know, the Web of Time, all that malarkey?
THE DOCTOR: Lucie, the thing is ... the Web is resilient. Events can be reshaped, can reflow. If your Aunty Pat lived a quiet unobtrusive life, never got married, never had children, never did very much of anything, then ... well...
LUCIE MILLER: Oh my God. I said it herself, didn't I? She didn't do much with her life. She was never a big noise.
THE DOCTOR: Well then ... history could ... blink and miss her. - The Zygon Who Fell To Earth

So it's more accurate to say that the Spiral Politic/Web is a map created by the Time Lords.

THE SPIRAL POLITIC [Terminology] [...] the best (colloquial) definition might be, the parts of history that matter. The Spiral Politic can be thought of as a map of the time-aware cultures of the universe, those cultures which have either begun developing time technology for themselves or been introduced to major time-active powers like the Great Houses, the Celestis and Faction Paradox, and also includes all those areas of the universe comprehended by those powers. However, the map is hardly a geographical one. Physical space is rarely in issue for the major powers – the timeships of the Great Houses have great difficulty with the concept of “distance” – so whenever the Spiral Politic is charted, the purely physical locations of things are largely unimportant. Naturally, those worlds, species and organisations which make up the Spiral are spread throughout the span of recordable time, and it might therefore be useful to think of it as a chart of occupied history…but even so, there are distinct relationships between worlds. Undoubtedly, any map of the Spiral Politic would have the Homeworld of the Great Houses at its core. The lodestone around which history revolves, cut off from normal-time and (theoretically) impervious to outside forces, it’s the one part of the map supposedly guaranteed never to change. In fact many time-active cultures argue that the Houses created established history, not in the sense that they plotted out every future event in advance but in the sense that they created the framework of history within which sentient species could understand their relationship to the past, the present and the future. If so, then it could be said that the Spiral Politic came into existence on the very day the Houses locked the framework together.
If an observer were to scale the map down into two dimensions, then he or she would see the worlds on the outer edge of the Spiral (i.e. those less intimately linked to the Homeworld) constantly moving, shifting into new positions as their roles in history change and new Wartime alliances are made. Indeed, the defensive strategy of the Great Houses can probably best be understood as an attempt to keeps everything as still as possible. On 2D map, the worlds immediately surrounding the Homeworld (i.e. those over which it has most influence) would appear to be rock-solid, bulkheads against the uncertainty in the further reaches of the Spiral. Any movement among these worlds would be ominous indeed. More ominous still are “shooting star” worlds. Nothing creates more panic on the Homeworld than the sight of a previously static world suddenly and unexpectedly shooting across the chart, often in the direction of the Homeworld itself. Again, this doesn’t mean the world is actually, physically moving: it means that its relationship with history, its own timeline, is being drastically altered. Those with a reasonable understanding of Spiral mapping have speculated that if a significant enough world were to “collide” with the Homeworld itself, then that planet would immediately take the Homeworld’s palace; the chain reaction would re-form the continuum so that the planet had always been the centre of history; the Great Houses’ influence would be utterly wiped from the timeline; and the War would end in a victory for the enemy. But today, fifty years after the start of the War, both sides in the War have become well-entrenched across history and the days of such lightning strikes are long gone.

It even includes locations beyond the Frontier of Time that the Time Lords control.

The posthumans, whose most powerful cliques exist over two-million years after the fall of Earth, are one of the few species-groups to have become time-active by their own will rather than be cause of interference from the major powers. This makes it difficult for the Homeworld to chart their worlds in the Spiral Politic, and many maps of occupied history feature great black swathes beyond the posthuman age which might as well be marked “here be tygers”, and which alarm the Houses as enemy forces could easily be concealed there. Earth itself remains surprisingly stable, the bridgehead between those parts of causality controlled by the Homeworld and the posthuman worlds themselves. Posthuman cultures include Siloportem, the capital city of the posthumans’ “decadent” faction, of such importance that on the map it’s larger than many complete star-systems. Frontier Worlds. Even the knowledge of the Homeworld has its limits. The Great Houses have particular difficulty analysing those cultures which exist at the far-forward end of time, not because these worlds are in the distant future (the term is meaningless to the Houses)but because there are so many other time-aware cultures in the later universe that all sorts of factions are able to muddy the waters. On the map of the Spiral Politic there’s quite clearly a “frontier in time”, beyond which the Houses have difficulty speculating, and as a result the world of Zo la Domini – situated right on the cusp of that frontier – has been the subject of much scrutiny.

When the Second Wave damaged the framework where Ordifica rested in the Spiral Politic, it was explicitly a breech in the entire continuum.

Destroying worlds is easy: making sure they stay destroyed, in a War where temporal confusion often leads to battles being replayed to the point of insanity, is harder. It’s a measure of the Second Wave’s zeal that the method they chose to eradicate Ordifica has since been officially condemned even by the War-time ruling Houses. The strategy didn’t simply destroy the world but punched a world-sized hole in the framework of the Spiral Politic itself, a gap in history, a breach in the continuum which neatly ensured that there was no way of re-writing this final, terminal version of events. Time-travel can change the history books, but at the site of Ordifica there’s no longer any “paper” on which history can be written.

The Earth is a nexus world that affects intergalactic history. So, contradicting certain events in the Web of Time can literally damage history.

Qixotl had good reasons for asking the humans to the auction. Earth was a low-interest world, according to the techno-pundits, but it had a kind of political value. The place was a nexus world, just like Dronid, or Solos, or Tyler’s Folly; insignificant on first sight, but when you looked at the bigger picture, you realised it was linked to the destinies of a whole host of intergalactic powers.

DOCTOR: And that would please you. Look, don't worry. Earth survived with minimal damage. It's an historical fact.
LYTTON: Yes, it's now become part of the Web of Time in the same way that the Cryons were destroyed.

PERI: Earth's safe. So is history and the Web of Time.

In Neverland / Zagreus, it's explicitly stated that Web of Time covers the past, present and future.

DOCTOR 6: Imagine this king now governed time itself, governed its use, its roadways. His was the past and the present. The future, too.
DOCTOR 7: And that's the interesting bit. What would have happened if this king had not woven his Web of Time?
DOCTOR 5: Why, his empire would have fallen. They always do. A matter of simple evolution, you know. Made extinct by the next dominant species. Happens all the time.

Including everywhere and when The Doctor and Charlotte Pollard have travelled.

CHARLEY: It's all right, Doctor. I'm not afraid. It's like I said in the Tardis. My time is up. There is no alternative. Oh, Doctor, you rescued me from the R101. You gave me these last few wonderful months. The things that I've seen, the places I've been. I've lived more than I ever could dream of, and all thanks to you. And you're the sweetest, the kindest, most wonderful man I've ever met. And I'm sorry it's come to this, and I'm sorry it has to end like this, but if the Web of Time is destroyed then all the time I've had, everywhere I've been, all those fabulous, fantastic things we've done, they won't ever have happened at all. Don't let those times be taken away. Don't let it all go to waste. I know it's an awful, terrible thing, but I want you to do it. Oh, Doctor, please do it before it's too late

The protocols of the Time Lords (such as the first law of time) and the—they're immutable enough that even the Time Lords would have to re-write history from scratch.

The truth is that although it was never recognised by House doctrine, the Yssgaroth atrocity was never entirely scrubbed from the continuum. The Yssgaroth entered history as history came into existence, so there was no real chance of completely removing the taint without ripping history apart and starting again from scratch.
Meanwhile, Faction Paradox is unique among the Houses in that it has no written Protocols of its own, but the truth is that the unwritten Protocols affect the Faction just as much as they affect the other Houses. In this respect, it might be said that the Faction’s chief aim has always been to break the covenant and no longer be subject to the rules of the House founders, yet in order to do this the Faction would have to remove all traces of Homeworld culture and technology from its ranks… either that or re-write the continuum from scratch.

Here's a very silly diagram of what a few striations of the Web of Time could look like. For reference, certain paradoxes or events/things that never truly happened/shouldn't have existed (never-weres) can still affect the primary timelines due to time travel, i.e Daleks from Day of the Daleks were from an alternate timeline where they took advantage of a Third World War caused by a paradox of their own making to successfully occupy Earth in the 22nd century, and this timeline interacted with/affected UNIT's own history.

The star used to create the Eye of Harmony underwent a forced supernova to fuel early time travel experiments.

DOCTOR: It was Omega who created the supernova that was the initial power source for Gallifreyan time travel experiments. He left behind him the basis on which Rassilon founded Time Lord society, and he left behind the Hand of Omega. - Remembrance of the Daleks

Following this, the collapsing star itself was converted into a harmonic power source (aka, the Eye of Harmony) by Rassilon and his goombas.

WOMAN: And Rassilon journeyed into the black void with a great fleet. Within the void, no light would shine and nothing of that outer nature continue in being, except that which existed within the Sash of Rassilon. - The Deadly Assassin

So, the semi-mythologised account hasn't been retconned. Omega allowed the Time Lords to have power over time and came up with the theory before he fell into the collapsing star, but Rassilon was actually responsible for it happening.

Rassilon designed the Web of Time to coalesce all alternatives into the Web of Time, creating no alternatives within.

RECORDER: File Ras/delta gamma. Seventy spans have passed since Cardinal Rassilon began investigating alternative realities. Alternative pasts, alternative presents, alternative futures. He discovered that all futures coalesce into one Web of Time alone. Free will is not a possibility. Alternative realities are not a possibility. When this universe was created, it brought into existence a race of creatures.

And the Web of Time is the limit of the Time Lords' reach.

Paraward, we find a sheath of histories which are either eternally separate from our own anchored time or which diverge and return to it so far in the past, or so far in the future, as to be – functionally – eternally separate from it in terms of the noospheres of the Great Houses. The physical laws of these universes are identical to ours, but all else is different. We call these paraward space-time entities ‘parallel worlds’. - The Brakespeare Voyage

When two full alternatives existed at once in established history (including two Romanas, and two contradictory adventures with The Doctor) in Enemy Lines and Collision Course, the Eye of Harmony was strained and/or powerless. Plus, universes simply don't have the resources for that.

LEELA: What is temporal divergence?
DOCTOR: Did I ever tell you how important it is not to temper with history?
LEELA: Several times.
DOCTOR: Well, if you ignore me, temporal divergence results. And the prime timeline, the established course of history, will split, and a new timeline form. Leela, the universe cannot contain two timelines, so the one has to cancel the other out. If the changes are small, the differences iron themselves out, time getting back on the established track as quickly and simply as possible.
LEELA: If the changes are not small?
DOCTOR: Ah then we have two possibilities. Either the alternate timeline pushes forward and creates a new universe sealed away in its own little bubble of reality. Or...
LEELA: Or?
DOCTOR: Or the entire fabric of reality falls apart and we are all erased from existence.

‘On second thought, that’s not right either. Only one universe can exist, the laws of matter and energy dictate that inescapably. I have travelled into the future of the universe, crystallized moments of it, from a point in my personal timeline before I was apparently killed. If that happened then Ace’s universe, the universe in which I am alive is the real one, ergo this one cannot be, therefore I was not meant to die, and... hmm. Suddenly I’m very confused.’ - Blood Heat

Similarly, Anti-Time, the opposite shadow created in the Web of Time's wake brooks no alternatives.

ROMANA: The Eye of Harmony created a universe of positive time, finite time. Gallifrey anchored the continuity of the universe. But just as matter has its counterpart in anti-matter, just as every action has an equal and opposite reaction, then, by all the immutable laws of the universe, positive time, the Web of Time, must have its shadow.
DOCTOR: Anti-time, as intractable and destructive a force to causality as anti-matter is to space. Something with no past, no present, no future. A perpetuity of meaningless chaos. A now, with no beginning or end. Elegant. Brilliant. Thoroughly logical. And utter gibberish. I've been trolling about the space time vortex for a lot longer than any of you. If there really was another plane of cause and effect, don't you think that maybe, just maybe, after all these centuries, I might have noticed? - Neverland

But anti-time is still able connected to alternatives in more than just possibility. For reference, the 'timeless diamond' is the Council of Eight's artificial version of N-Space, the 'terrible mind powers' one refers to Death Comes to Time, and the Earth where The Doctor 'plucked out one of [his] own hearts' was a semi-cancelled timeline from BBC's Eighth Doctor Adventures.

DOCTOR: Yes, yes. And between them they bore witness to a billion alternatives. I can see things in my mind's eye. I can see me, thousands of mes doing difference things in different places, but all at once. Alternative realities. Or maybe this is an alternative, and one of those others is real. You're part of me. Can't you see what I'm seeing?
ZAGREUS: Always.
DOCTOR: Look there. I see myself on the planet Oblivion, facing a race called the Horde. And there, look. A tiny reality where Gallifrey isn't a planet but a timeless diamond, drifting through the stars. I can see a universe where the Time Lords have terrible mind powers, and another where they have ceased to exist. Time wound backwards to eliminate their every trace. A planet, Earth, where the Nestenes very nearly destroyed everything. And another Earth, upon which I have plucked out one of my own hearts. But which is real, and which are the alternatives?
ZAGREUS: There is no alternative.
DOCTOR: You mean no one knows which reality is the real one?
ZAGREUS: They are all real, and primary to their inhabitants. In the grand scheme of things it doesn't matter. Who is there to care? They all exist, occasionally sharing moments, eras. The rest of the time self-contained and unaware. But all are destined to end together, and very soon. - Zagreus

Also, the Caldera is the crater formed by the Anchoring of the Thread. Since it's basically the primary node point of history, it can influence everything that's within the meta-structure of the Web of Time (since The Eleven Day Empire was literally build from the same technologies that made the Anchoring, it's de-anchored from history, and thus immune). Yet, the Caldera is capable of reaching alternate realities, and can manipulate them.

Someone in this novel-world is planning to rewrite history. Whoever it was already has the power to do that in minor ways, like writing me out of the world, but give somebody the caldera and…well, put it this way…the caldera can rewrite the history of more than just one universe. And influences can travel from books to their readers quite easily. If I was reading this book, I’d be really hoping the goodies win. - Head of State

In fact, the Eye of Harmony can suck people into parallel universes.

DOCTOR: Engin, that Sash is a technological masterpiece. It protects its wearer from being sucked into a parallel universe. All he needs now is the Great Key and he can regenerate himself and release a force that'll obliterate this entire stellar system. - The Deadly Assassin

Platonic Forms

I was told the description of Platonic forms in The Book of the Enemy could get some high results. For reference, the author of the story is a fan of Plato's works.

The Enemy and the Time Lords (due to their relationship with history and ability to literally manipulate concepts) are described as living ideas and impingements on the 'reality of the eternal forms' that Plato wrote about, implying Plato's description of form is accurate, and the wartime powers are an exception.

‘An idea can…wait. You’re talking about magic. You’re talking about people’s minds changing the world. That’s magic. Are you saying magic exists?’ ‘Well, yes and no. Yes, magic exists, but no, ‘people’ have nothing to do with it. The beings we are talking about are not people in any sense we would use the term. They are much more than that. One might call them living ideas, and wherever and whenever they go, they reshape reality around themselves. The very currents of history are shaped to their whims, and a mere thought from them can cause a civilisation to rise or fall. One might think of them as impingements on reality of the eternal forms your Earth philosopher Plato wrote so eloquently about. They are eternal, and exist in all times and all places at their whim.’

Later, the two powers are described as literal platonic forms.

‘Yes, I believe so. The ambassador talked of a war between powerful factions of gods – a war between ideas, Platonic forms.’ ‘That appears to be the size of things, yes.’

Since the main characters live in the world of Euclid and Plato, they're bound by the facts of the 'real world', but these facts about Platonic Forms aren't necessarily true since they only describe the intrusions Platonic Forms into the real, Euclidian world.

‘But how can Platonic forms be at war, Holmes? They’re eternal and unchanging – that’s what it means to be one. A triangle can’t go to war with the concept of justice!’ ‘Ah, but it can. And indeed that is precisely what is happening. Have you ever heard of non-Euclidean geometry?’ ‘I confess I have not.’ ‘It is a branch of the pure mathematics originally conceived by Herr Gauss, but taken to its most refined form by my old adversary Professor Moriarty, whose observations of asteroidal dynamics led him to create his famous theory of relativity, which is only now, some thirty years later, gaining widespread acceptance. It is a mathematics in which a triangle may have angles which add up to more than – or less than – one hundred and eighty degrees. A mathematics, in short, in which a triangle is not a triangle. And Moriarty showed, with his astronomical observations, that this is the mathematics which actually applies to our own universe. Triangles as we understand them now exist only in men’s heads – the real world now only has triangles which are not triangles at all. A fact about the Platonic Forms which we all know to be true – and to this day one can still prove with ruler and compasses that a triangle must indeed only have one hundred and eighty degrees of angles – is false as it applies to their extrusion into the real world. The triangle – and the square and the circle – are now merely fictions, and we live in a world of non-triangles, non-squares, and non-circles, even though our minds tell us otherwise.’ ‘Holmes, this sounds like a nonsense!’ ‘The modern mathematics does, indeed, sound like nonsense, and many men when confronted with the facts simply refuse to acknowledge them. But they remain the facts. And once one has read Moriarty’s On the Dynamics of the Asteroid, one knows the truth – we are living in the world described in Moriarty’s book, not Euclid’s.’

For example, a piece of Enemy technology (the titular Book of the Enemy) is able to consign fact to fiction by changing Euclidian reality's relationship with Platonic Forms, with Holmes, Moriarty and The War of the Worlds previously being real before The Book of the Enemy erased them.

‘But Holmes, you can’t be arguing that Moriarty’s book changed the nature of reality?’ ‘I do not rule out the possibility, though I confess that my own understanding of celestial mechanics was never such that I could have described, prior to Moriarty’s work, the current state of affairs. I cannot be sure that the nature of space was ever other than it is. But whether or not he did, one can see from my example how a book can change the nature of reality’s relationship with the Platonic forms, yes?’ ‘I’m not entirely sure I follow, but carry on…’ ‘Now look at this.’ Holmes handed me a book, and I examined it. The War of the Worlds by H.G. Wells. I opened it and noted its indicia, stating it was first published in 1897, and then started to read the opening paragraphs – which I have since committed to memory: No one would have believed in the last years of the nineteenth century that this world was being watched keenly and closely by intelligences greater than man’s and yet as mortal as his own; that as men busied themselves about their various concerns they were scrutinised and studied, perhaps almost as narrowly as a man with a microscope might scrutinise the transient creatures that swarm and multiply in a drop of water. ‘Holmes!’ I exclaimed after reading a page or two, ‘surely this is a history of the late war? Some evidence that our senses were not mistaken, and our memories not incorrect?’ ‘Alas, I fear not,’ he replied. ‘That book did not exist last night. I found it on my bookshelf this morning, in the small section I have devoted to romances. While this book accords with my memories in all its particulars, it nonetheless purports to be a work of fiction, and has been taken as such by the general public, in much the same way as you view Ruritania as an imaginary land rather than the very real place it remains in my own memory.’ ‘So when you talk about books…are you saying that people are writing books and somehow…capturing reality and making it fictional?’ ‘Ah!’ he laughed, ‘so close and yet so far! No, how could writing a book make reality into a fiction? No, my contention is that people are reading a book, and that book is changing their ideas, and thus the nature of reality. In fact, I believe they are reading a very specific book.’

It's later stated that the account in this story might not be accurate, but at least the ideas in it are real.

They are not themselves the Enemy, but they have been at times useful idiots capering in its shadow. However ignore the full range of sources the good theorist does not. We cannot know at this time, the truth or falsity of the following narrative in its ultimate details, although the majority of it is plainly and simply factual. This may be part of its danger. In my time there was a fiction of an evil man, Doctor Mabuse, who – though he died – still left a testament, an embodiment of his will, by which others were made over into his image. In such stories as these from the legends or propaganda of third parties we see the fingerprints (if fingers they may be said to have) of The Enemy’s Testaments.

ByAsura · Dec 26, 2023

Mathematics

One particularly consistent aspect of Doctor Who is that, at least from the perspective of the Time Lords, the universe is essentially just mathematics.

The Matrix is the repository of all knowledge. It contains all the mathematical axioms and scientific principles that govern the universe, and can apply them a great deal more efficiently than anyone Gallifreyan. There are no mysteries to the Matrix.’ - Infinity Doctors
'It's perfectly simple. The universe is basically infinite, because it has no exterior boundaries. At the same time, because any finite number divided by infinity is zero, then although the universe has eleven dimensions it is also a single point with no dimensions at all. Since there is nothing outside then nothing can enter or leave, and all that can happen is that the state of its contents can change. [...] Now, because the universe is an infinite single point there's no reason why you can't go from one point to another instantly on account of the fact that you aren't actually moving because you're staying put in the one point that is the universe. Since time is just another dimension also divided by infinity, the same principle applies. All you have to know is how to get down to the basic building blocks of reality.' 'Which are?' 'Numbers,' the Doctor said simply. 'The essence of matter is structure, and the essence of structure is mathematics. When your physicists get around to investigating quantum mechanics and sub-nuclear physics, they invariably find that even the smallest particle is always made of some thing even smaller. There always follows a point as which that some thing smaller is too small to have a physical existence and can only exist as a mathematical concept in the mind of the observer. All you have to do is manipulate those concepts to effect changes in the physical universe - turn parts inside out as TARDISes, warp space and time, hop between dimensions, all that sort of thing.' - First Frontier

For example, The Book of the War depicts high order mathematical structures as the equivalent of Loa, who are literally embodiments of time.

LOA [Faction Paradox: Legendary Participants] According to the Great Houses, time may not be simple but it’s at least logical. Time can best be understood in equations, in models: the workings of history are high order mathematical structures, certainly complex but (given a large enough computer, say, one capable of decrypting entire universes) still explicable as nothing more than numbers. Faction Paradox, on the other hand, is an organisation obsessed with alternative-time systems. To the Faction, the processes of time aren’t formulae or theoretical concepts. The processes of time are entities. Time is occupied, even guarded, by loa which have no tangible presence in the universe but which can protect, beguile, curse and possess anybody who tries to cross their boundaries.
Andraiz staggered a little as the spirit that anchored the time–loop gently pawed at him, a needle skip–skip–skipping into a new groove. - A Romance in Twelve Parts: Tonton Macoute

Christmas on a Rational Planet even implies that debunking the Pre-Universe's strange physics was part of the Anchoring of the Thread.

The Watchmakers. Logical, masculine creatures. They rejected the possibility, and denied the world of wonders. Perhaps it scared them. They wanted existence to be precise, to be mechanical, so that they could live their lives to a solemn timetable. They wanted to understand the universe in the same way you might understand a piece of clockwork. As a cold machine. No room for cities of brass or dragonfly-gods. They invented rules, and tied creation down to those rules. [...] Yes. They were beings of Reason. They proved that horses couldn’t fly, so horses didn’t fly. They proved that cities couldn’t dream, so cities didn’t dream. The shadeling gods, the children of the Pythia... one by one, they all died, pushed out of a cosmos that was too rational to let them live. The Watchmakers took away the glamours and the mysteries, then built machines in their places. They became kings of Reason. Masters of space, lords of time

To Gallifreyans, Quintessence (upper-case) is a rank, but quintessence (lower-case) is depicted by The Book of the War as an analogue of the classical Aether its more modern equivalents, which served to explain some universal complexities in antiquated science.

QUINTESSENCE [House Military: Culture] In alchemy the name given to the “spirit”, necessary to infuse and inform earth, air, water and fire. In late twentieth-century Earth science, the name given to the predicted “dark matter” needed to reconcile apparent galaxy movement with known gravity. Any hidden variable whose existence is needed to allow two contradictory-but-valuable beliefs to co-exist is known as quintessence. By the Seventh Wave of the House Military, Officers of the Quintessence were serving in most forward positions as bridges between the pure military ethos of the House militia and the more rarefied musings of the time strategists. Though it’s the duty of such an Officer to act as an intermediary rather than a great leader, notable Officer shave included Quintessence Hierarchio (whose Seventh Wave cohort discovered virtually everything that’s now known about the immense, universe-like Leviathans) and Quintessence Redloom (later a General, and often said to have been involved with the founding of the soldiers’ Redemption Cult).
Against Nature

Against History (created well after The Book of the War) describes quintessence as the underlying archemathic (which is often described as symbols, code or arithmetic) layer of the entire Web of Time/some artificial parallel universes. The Time Lords, of course, manipulate it to command aspects of the universe.

She had been trapped inside a bubble of orthogonal spacetime, an improbable variant form of existence, myths and legends forcibly stamped onto the quintessence underlying the spiral politic.
'The quintessence is the most fundamental level of being, the archemathic medium upon which the matter and meaning of the spiral politic is inscribed. A different system is being introduced, and somehow, you and I are part of the mechanism by which this is happening. From what you have told me, you have already noticed some changes in your life, occurrences which would seem to contradict the established laws.'
This bubble universe behaved as though it appreciated gravity as aconcept; yet there was neither gravity nor electrical force nor even anything resembling the noösphere promised by the terrible, overbearing sense of death of which the wraiths were only the most vivid expression. The archemathic information of the realm had been unreadable even when House Meddhoran was in possession of instruments by which such material could be read.
Gedarra and Rhodenet's cognition would be entangled allowing for remote communication even across divergent universes - providing both locations had grown from the same basic archemathic quintessence. The operation might once have been performed in the blink of an eye by means of gietesphere, but Gedarra would be required to spend many housedays going over the code, manually catechising her own biodata.
The final archemathic characters were rendered. Rhodenet's great catechism achieved critical mass, unravelling the deep structure of the flaw from the other side, the other side being the nearest point where the quintessence actually supported a structure to be unravelled.
'The breeding engine is, as I understand it, an aspect of the caldera. The archemathics involved are unfortunately beyond definition by means of ordinary language. Sadly, it is not a ventilation tunnel through which we might crawl in order to return to the spiral politic, assuming your thoughts ran along such lines.'
In his left hand, the brush bywhich he painted tiny characters and archemathic symbols upon the stones.
Each part of the chapterhouse sloughed off information as it regressed to an earlier form; and that information coalesced within the athenæum, condensing into raw archemathic code scratched upon rough, yellowing paper - the base numbers of quintessence transposed to ink.

Of The City of the Saved... confirms that Archemathics is a Gallifreyan discipline, and a form of mathematics that describes the underlying structure of a universe, making conventional physics look like a joke, despite the fact contributors to Archemathicists in the book study 9th dimensional ur-solids. Depending on well versed someone is, they can mathematically model structures (even in realspace), including universes.

Also, natural-born TARDISes like Antipathy have Archemathic exterior shells. This strongly implies that Archemathics are actually Block-Transfer Computations, but there are some inconsistencies between the portrayal of BTC and Archemathics.

Conceptual Space

These quotes are all from The Book of the War and The Taking of Planet 5.

The difference between a conceptual entity and a memetic entity is that the latter is simply made of ideas. Conceptual entities aren't just made of ideas, they exist purely as conceptsand inhabit the meaning of things between matter itself. But this also means they're limited on ideas for some kind of substance.

CONCEPTUAL ENTITIES [Celestis: Engineered Participants] Engineered beingsor weapons (in many cases conceptual entities are both) which exist only as concepts, and have no provable substance at all.
This is a reasonably subtle idea, and several cultures involved in the War have had difficulty grasping it. As conceptual entities only seem to affect the minds of their victims, it’s often said that the entities are ‘made out of pure thought’, but this is clearly inaccurate as thought itself isn’t a substance. Although many people are determined to think of the entities as telepathic presences, or neurological parasites, or in some cases even “spirits”, in fact it’s much more accurate to think of them as nothing more than hostile ideas. They exist by bypassing matter altogether, and instead giving themselves structure inside the meanings of things.
Despite their claims to be the true aristocracy of the universe, watching the War from outside the Spiral Politic’s walls as if it were a mere amusement, the truth is that the Celestis’ power is distinctly limited: every Lord of Mictlan is secretly aware that he or she depends on the lesser species to have any substance at all. Fear has traditionally been their best weapon, and Mictlan, with its towers of blackened metal, its factory-smoke walls and its seas of all-consuming empty space, has fear worked into every conceptual minaret and every memetic foundation-stone. Or alternatively, perhaps it’s the Celestis’ own fear that’s given Mictlan its shape.

Even if an object is erased from history, it still exists with memetic mass if someone remembers it. Alternatively, if a person is transposed within their own timeline to the point where it falls apart, they're kept together by memetic connections.

It was known that with the correct application of technology, an object or individual could be put into a forced-paradox state in which that object was entirely removed from the timeline as if it had never been there. Yet although this process removed the object’s matter from the universe, an observer in a null-zone state could still remember its existence. Therefore the memetic mass of the object – its meaning, its importance, its ability to be comprehended – remained. The object survived, but as a pure concept of itself, as a shadow of understanding with no physical mass. It was the same principle which would, once the War began, be used to create the conceptual entities.
FLUXES [Celestis: Engineered Participants/Technology] Individuals transposed backwards in time but not too far in space, using a very high chaotic limiter setting and tied to their home period by a thread of biodata. The subject is turned loose in his or her own history, and the limiter setting allows tiny actions taken by the future version to have considerable effects on the past version. The biodata link then transfers these changes to the future version, which alters it, and thus alters the changes made to the past version. Therefore, the individual’s history is kept constantly in flux. [ [...] There are suggestions of a stable middle-ground between the two fates, in which the physical matter of the flux is lost but the meaning of the subject/victim is retained, a series of memetic connections with no flesh to support it. Yet this entity exists only on a purely theoretical level, relying on the perceptions of others to survive at all. In theory these fluxes exist only as repeating patterns in the temporal shifts, in the same way that carbon-based beings exist only as repeating patterns in transient matter. As a result, such carefully balanced fluxes are sometimes referred to by the medium in which they prosper: Shifts.

During the War in Heaven timeline, the Celestial Intervention Agency created a memetic realm (not actually a conceptual realm, mind you, but technically a conceptual ecosystem) by erasing themselves and a sizeable portion of Gallifrey from existence, allowing them to exist as memetic mass on the outer conceptual edge of the universe.

Still believing themselves above the material universe rather than dependent on it, they sit comfortably on their thrones in the towers and fortresses of Mictlan, watching events in the outside universe (or rather, the inside universe, as Mictlan exists on its outer conceptual edge) like the bored Gods they believe themselves to be. In truth they have very little effect on the War, perhaps being too terrified to involve themselves in the universe they so readily escaped, but in recent years those Lords who see the War as a kind of game have begun to interfere and take sides.
MICTLAN [Celestis: Location, Major Powerbase (World)] There is, for obvious reasons, no record of how the Celestis managed to remove themselves and all traces of their history from the Spiral Politic. It’s been suggested that the technology which cut them out of the physical universe might have been supplied by the Godfather-lieutenants of House Paradox, as the Grandfather of the House seems to have been scrubbed from the timeline by a similar process (although compared to the Celestis, the Grandfather seems a positively benign presence). Whatever the Celestis did, they did it not only to themselves but to a sizeable portion of the Homeworld. Those agents of the Houses who possess deep-time memory – the ability to remember past-iteration events even if they no longer actually happened – record that there was once an academy on the Homeworld which was used as a prime recruiting-ground by the hard-line intervention groups, and which withdrew from the academic roster mere days before the Celestis seem to have wiped themselves from history. Nobody else has any recollection of this academy, however, so it’s fair to assume that it was removed at the same time as the Celestis themselves and turned into the extra-spatial realm of Mictlan.
The Celestis are, at least in part, a race of high-intensity conceptual entities. It’s therefore not surprising that the Celestis are still the masters of conceptual engineering, and in recent years those Celestis who oppose the Homeworld have supplied the enemy forces with a whole host of specially-designed military concepts. The most blatant of these are, of course, the anarchitects. To some extent the Celestis’ realm of Mictlan is an entire conceptual ecosystem, and is thought to be unique in this respect. [See also fluxes.]

Mictlan is a metaphysical bomb shelter that's even outside the effects of the Time Vortex. Since it's in a constant state of flux, it's literally poisonous to reality.

Even Mictlan itself can be considered a kind of enormous flux, an endlessly shifting realm so corrosive to the rest of history that its heartland has to be kept on the outer skin of the universe. Celestis conceptual entities such as the anarchitects and the gargoyles are also dependent on flux theory.
They had poisoned the walls of reality itself, until Mictlan had bubbled up into existence on its far side, a cyst of galled space-time cut off from the time winds. It was their glorious world of the dead.
Mictlan was – in its origin – a metaphysical bomb shelter. Removed from space-time, it and its occupants (if the two could in any real sense be distinguished except at the most simplistic of levels) were, in theory at least, immune to the time winds, to the possible changes being, or to be, wrought by the war. In theory, even if the Enemy had turned primordial Gallifrey into atoms or defused Omega’s stellar manipulator, or aborted the Time Lords’ history in any way, Mictlan should have remained – a node of information from a previous space-time preserved after its collapse by the lack of a causal connection between itself and the war.

So, the idea of N-Space exists outside of N-Space itself.

Warp Space

In The Last of the Cybermen, The Doctor describes warp space as 'a sort of secret passage through normal space'. Exiting warp space creates spatial disruptions in realspace and 'hyperspatial turbulence' within any ship.

10 years prior to the story at the end of the Cyber Wars, a vast Cyber-Fleet disappeared into warp space above Telos to attack 'Earth's galaxy' (meaning warp space can cover intergalactic distances). They were contained with the confines of the Kuiper Belt, yet they didn't appear on any scanning equipment or even to human eyes.

When the beacon was reactivated, a C-Class Cyber-Vessel was able to time travel back to Telos at the end of the Cyber-War through warp space. The Cyber-Super Controller schemed to have the armada stationed at the Kuiper Belt attack Earth in the future (as The Doctor and his companions arrived from the future where the Cybermen lost 10 years ago, meaning the Planner had to retain historical continuity), but the fleet was manipulated to collide with Telos in the past, which ultimately maintained the original flow of time.

So, warp space provides intergalactic and time travel, but it's far more limited than TARDISes.

Human starships travel through warp space (where stars aren't visible) to move at FTL velocities.

A small starship flits through warp space. One of its networked picoprocessors carries the mail: its ROM-store contains a stack of silvery needles embedded in non-conductive plastic.
Defries shook her head. It was late, and she had to go into warp space tomorrow.
Far away – five weeks away at warp speed – Francis was feeling ridiculous.
Everything was going just fine. It wasn’t impossible to intercept a ship in warp space, but nothing had disturbed the progress of the Admiral Raistrick. It was very nearly too late to stop them now.
‘The other auxies have spent the last month in deep-sleep, or using up the booze and other substances I let them smuggle on board. You’ve been working out every day, you’ve been using the ship’s data net, and most of the time you’ve been on the bridge getting friendly with Captain Toko and his crew.’ ‘I like the stars.’ ‘We’re in warp space, trooper.’ ‘But I know they’re there. I like to know we’re moving.’
The closest face, the one directly behind the troopship, the one they had almost hit when dropping out of warp space, was lopsided, with huge filigree ears and an expression of mournful anguish.
Radio waves, travelling only at the speed of light, were much slower than warp-driven vessels and were used to carry communications only within planetary systems. - Deceit

It's implied to be a different layer from space.

‘Well. No one really knows how, but the Artifact warps space. Gravity is weird in here. Instruments give conflicting readings. There was a theory that the thing could extend into warpspace, that it might even have caused the ship to crash here, all those hundreds of years ago. And if that’s the case...’ - Parasite

Miscellaneous

In The Auntie Matter, Romana I derides the human sciences of the 20s (specifically noting that humans have recently 'figured out general relativity') as 'barely one step up from banging rocks together.' In order to 'while away the afternoon', she reads literature of recent breakthroughs in science and mathematics, including set theory, quantum theory, and the photoelectric effect. So, set theory exists in Doctor Who, but it's utterly primitive.

The Time Traveller's Diary confirms that wave functions exist. And like I said before, Daybreak explains that probability waveforms can collapse.

Idk what this means for ratings exactly, but apparently it's useful.

They exist. I have no idea how this affects the cosmology, either.

‘Don’t worry about it, Doctor. It can’t be any greyer than it used to be.’ ‘But I think it’s all there. Ask me a question.’ ‘A question?’ ‘Yes. Something really challenging. N-dimensional geometries, that sort of thing.’ - Deceit
'We are setting up listening posts throughout this dimension, all looking for the specific materialisation signature of the Doctor's transmat capsule. The N-Dimension nano-cameras are in place and set to a rolling frequency to avoid detection. They will continue to breed and secrete themselves on him, his capsule, his friends, the other agents when he meets them. We will get unlimited access to all that they encounter.' - Short Trips: Monsters - Best Seller
The man known as Griffin was in a library, just before closing time. A fine thread of biodata ran through the back wall of the building, an n-dimensional line of information spun out finer than the finest skein. It ran at an angle, crossing the car park, passing harmlessly through trees and light poles and a snuffling dog, puncturing the building. - Unnatural History

Superforce also exists. And I also have no idea how it'd affect ratings.

“The Climb is a joke name,” Adam said. “A joke you should both get. We developed vunktotechnology, machines so small they could poke their fingers into a Planck length and play the harp with superstrings. Once you can do that, well, for starters, you have complete control of the fundamental superforce of the universe.”
The Doctor nodded. ‘Touch a button and no more enemy. No more traces of enemy. They’d be gone. The weapon doesn’t just kill them, it kills everyone who’s ever heard of them. Destroys everything they’ve ever built and drawn and written. Everything they’ve ever seen, even the stars in their sky. Erases it all. It’s a weapon that would give your run-of-the-mill ultimate weapon an inferiority complex.’ ‘How?’ Jeffip asked. ‘I mean, how could anything do that?’ The Doctor waved his hand airily. ‘Quantum physics. The observer effect. The superforce. Vunktotechnology. Vundatechnology. The people who built that weapon knew their stuff.’ - The Eyeless

String Theory is implied to be a relatively simple concept to relatively advanced multi-stellar empires, like the Slitheen, let alone the Time Lords.

TIME: Until then I'm stuck here, in this, teaching science on the planet Thick where they still haven't worked out string theory. Ooi, it chafes. - Revenge of the Slitheen
The Doctor smiled. Every child on Gallifrey knew the answer to a question as elementary as that. A classroom question – basic kindergarten eleven dimension superstring theory. - 13 Doctors, 13 Stories: Spore

Superstrings are part of the baseline substance of reality, meaning that anything composed of superstrings is virtually indestructible and extremely strong.

‘Don’t worry about the tents. They’re made from super-string taffeta. You run a thread through the substratum of the universe to produce a material that’s one part fabric and nine parts base-line reality. You could use it to wallpaper over a black hole.’
‘I imagine –’(He was at it again!)– ‘the pages are made from a superstring-reality-sub-stratum-material. For the Book to exist in all times and places it would have to be incredibly strong and durable. I don’t really have time to go into the physics. Suffice it to say it’s flexible, malleable, and has the same tensile strength as solid reality.’ - The Book of Still

Only the immense strength of the building and the partly extraphysical nature of its construction prevented the world beneath it breaking apart; as it was, the shockwaves destroyed the Spire and tore fragments of its mass through its own time fields. Wildly out of adjustment, the lashing super-strings sprayed mass forward in time in a great fountain of hyper-energies. Across the future, fragments of strange crystal fell like rain on the mossy fields of Canopus, blighting the crops. - Ghost Devices

Superstrings even extend into Hyperspace.

'That's the view that our astronomer associated with the ceremony called the Resurrection Dance...' The Doctor tapped the telescope. 'This uses lenses that are part of superstrings that lead into hyperspace. She designed it to see through all their stealth procedures. Do you feel bad looking at the sphere?' - Love and War

I will expand upon superstrings throughout the thread.

N-Space's Adjacent Dimensions

Technically, this should include Hyperspace, but I'll actually be covering that below for the sake of canon consistency (see Space-Time Vortex - N-Space's Vortex - Hyperspace).

Null-Space

Null-Space is a non-continuum, counterpart of N-Space that people go to when they die.

BRIGADIER: Yes... Doctor, what is N Space?
DOCTOR: Well now, the Earth - every world - has a counterpart. They're as close to each other as a pair of clasped hands. In the normal course of events, it's impossible to go there or even to communicate with it because... [...]
BRIGADIER: Well, where is it, then?
DOCTOR: Nowhere. Literally. It's a question you can't ask. There's no "where" for it to be. You see, N Space isn't in this Space-Time Continuum at all. That's how it gets its name. It's short for Null-Space.
SARAH: And that's why we're not aware of it.
DOCTOR: Yeah, precisely - because of the discontinuity that you might expect between the two worlds, which forms a very effective barrier. It can normally only be crossed by the dying.

DOCTOR: Yeah, I'll come to that. You see, every sentient being on Earth has an equivalent N Body, coterminous with the ordinary body.

Travel between the dimensions forms cracks in space.

DOCTOR: Yeah, well, the trouble is, with some people the mind is so attached to the things of Earth that they can't give them up. Well, often they can't even take it in that their Earthly lives are over. So, instead of just passing through, they get stuck in N Space. Some of them even try to get back through the barrier; and if they can find the smallest flaw, they'll come back and try to relive their final moments and make them come right.

JEREMY: Look at the light - it's like frozen lightning.
DOCTOR: You're seeing the cracks through the N Space barrier.

Shuntspace

Shuntspace is related to N-Space's Time Vortex.

'My lord: unless we can ascertain exactly what is going on we cannot be certain that we can getaway anyway.' That was a good argument: shuntspace was related to the Vortex. If one was behaving oddly, it was a fair bet that the other one was as well.
'Yes, my lord. Although the Vortex is unstable, shuntspace isn't affected. We can set off for Hexdane immediately.' Lassiter frowned: shuntspace was becoming more turbulent by the second. Why was Monroe lying to her saviour? - The Crystal Bucephalus

It's used for FTL travel.

[...] 'Delay? There isn't any delay, that's how long it takes. New Alexandria is on the edge of the Capricorn Tract.' '[...] Anyway, at shuntspeed fifty, it shouldn't take more thana day, surely?' Lassiter laughed. 'Shuntspeed fifty? What sort of ships have you been travelling on recently? They just don't go that fast any more. Things are rough out there, Doctor: widespread technological failure, insufficient funds or knowledge to replace the worn out equipment...'

Subspace

Subspace corresponds to realspace in some way.

Tapping away at the tablette, he shifted the readings from magnetic flux to the third derivative of gravimetric intensity, a sure pointer to any subspace activity which might have explained the infarction he had detected in the TARDIS.
‘When it’s finished, the GodEngine will be able to manipulate the electromagnetic, gravitational and subspace fields of stars. It causes stars to emit coherent, superluminal beams of plasma. It’s an FTL plasma cannon!’
Clearly, everyone was wrong. As the hundreds of saucers headed towards Earth at just under lightspeed – given the sheer number of ships, they would have had to have come out of subspace this far out to avoid problems with the sun’s gravity well – Julius opened a channel to Interstellar Taskforce Command.
‘If Felice finishes what she’s doing, the GodEngine will be ready to come on-line. They still need something which appears to be an ignition key, but once they’ve got that, the GodEngine will be able to fold the subspace manifold around stellar cores. It can create polarized funnels of subspace and accelerate coherent plasma down them. Imagine it: a plasma gun powerful enough to incinerate planets, to ignite superJovians, to turn stars nova.’

Humans and other alien species in the 22nd century used stunnels for instant travel. Stunnels are designed to rip through space-time and puncture the surface of subspace, creating a warped tunnel through subspace into which someone/something's component atoms ('subspace shadow') can be projected.

Transit technology had been all but abandoned years ago: human beings had never really trusted the idea of being scrambled into elementary particles and shoved through subspace, and the fiasco of the first commercial stunnel run to Arcturus hadn’t helped its popularity.
‘But the Transit beam never focused at the secondary node,’ Rachel muttered. ‘There wasn’t any way for matter to penetrate subspace and enter the stunnel stream.’ In simple terms, the subspace transit tunnel they had attempted to create– a stunnel – had only had an entrance. Creating an exit was the purpose of their research. A desperate purpose.
The pillar was one of the eight Higgs’s generators arranged along the length of the stunnel generator, equipment which created the elementary particles whose unique properties could open the subspace meniscus and rip the fabric of the continuum apart, granting them the access to subspace that they desperately needed.
Dr Felice Delacroix looked up from the board of readouts and frowned. Ten minutes ago, their latest attempt to punch a hole through subspace had gone rather spectacularly pear-shaped, blowing half the failsafes before dissipating into the void.
Rachel, Felice and Chris watched as her fellow colonists filed through the pulsing blue corridor into subspace. But where would they materialize? Was she saving them from one death, only to condemn them to another?
And then she was through the subspace meniscus and into the stunnel, and whatever lay beyond.
‘Not exactly,’ Felice replied. ‘On Charon, we could only weaken the boundaries between our dimension and subspace, create an entry and an exit point, and project matter through the tunnel we had created. This is far beyond anything mankind is capable of.’
She hit the incandescent exit point of the stunnel. Every particle of her being – and Felice knew the scientific name of each and every single one of them – turned inside out and collided, transforming her from a vague subspace shadow into - Whatever it was, it hurt. It seared every nerve ending with microscopic red hot pokers, taking her to a level of pain that she had never imagined existed. Any thoughts about the other end of the stunnel were overridden by an excruciating agony that seemed to last for an eternity.

Subspace is an abstract dimension with warped physics that will kill humans in a matter of minutes. It's not hyperspace, however.

She looked across the room to the huge oval of their stunnel terminus. Although it possessed none of the pizzazz of the old commercial termini such as Paris or King’s Cross, it had one thing in its favour: it was the only terminus in the solar system that still functioned, a fact indicated by the infinite cylinder which stretched from the mouth of the oval into infinity..., or so it seemed. Actually, it was an optical illusion caused by the universe’s interaction with the primary subspace meniscus. And reaching beyond that meniscus into the abstract dimension of subspace – with the blockade in place – might be their only hope of reaching beyond the solar system.
The moment that Rachel had dragged her through the weakened subspace meniscus and into the stunnel, Felice had known that something was wrong, and her entry into subspace had proved it. Immediately she had been immersed in the dimension, she had felt as if her hands and feet were at the ends of million-kilometre-long arms and legs, her body smeared across subspace – but that was not what it was meant to be like! From her degree and doctorate in physics, she knew that human beings couldn’t survive for more than about fifteen minutes in the warped reality of subspace before their molecules flew apart, but she no longer had any sense of time; she could have been in subspace for minutes – or hours, come to that. All she knew was that this wasn’t what she had expected.
For all she knew, Chris’s dissociated body could have been floating next to her, or even mingling with her, atom to atom. Ironic, she thought: what if the closest they ever got to sex ended up as a quirk of subspace physics?
Chris shook his head; although he had built toy warp engines for the spaceships he had modelled as a boy, subspace drives had been superseded by hyperdrives centuries before he had been born. ‘Sorry -’

Stunnels are poly-dimensional, and can failed ones can pull matter in non-Euclidian directions.

After tentatively emerging into reality, the funnel stiffened; it immediately grabbed trillions of tonnes of core matter –superheated plasma – in its poly-dimensional folds and pleats, before twisting in countless directions, none of them even slightly Euclidean.

When the Daleks invaded the solar system, they blockaded subspace with particles to prevent transit through the matrix that exists between subspace and realspace. This forced a research team to travel underneath their jamming fields.

However, events that had followed the invasion of Earth had given them anew purpose. The invaders had set up a subspace blockade across the solar system, making it impossible for any ships or supplies to drop out of subspace within the orbit of Cassius. And conventional travel was just as impossible; the Black Fleet simply blasted anything that moved. Rachel, Felice and the others were possibly the only people in the solar system with the faintest chance of breaking that blockade – not that they had much to show for it at the moment apart from a succession of failed, one ended stunnels.
Rachel answered as Felice picked up her tablette and started keying in data. ‘We’ve been looking at this the wrong way, Mr Cwej. We’ve been trying to counter the invaders’ field with brute force. They’ve flooded subspace with strange icarons, and we’ve been trying to punch through the interference – force our way through the non-aligned boundaries – by ramping up the strength of the stunnel carrier wave.’ She looked over towards a ruddy-faced man and beckoned him over. ‘Oi, Whiteley, get your arse over here.’
‘The Thornley-Ramsay Law concerns the penetration of subspace,’ she stated coldly. ‘It’s never been applied, because we’ve never needed to use it. It applies to situations when the subspace boundaries are non-aligned.’ She nodded towards one of the monitor displays, which showed an oscillating web of purple lines. ‘What is that supposed to be, then?’ he asked. ‘The matrix which lies beneath subspace,’ Felice explained. ‘The invaders’ jamming field works by shifting the boundaries of that matrix slightly out of phase, making it impossible to shift between the real universe and subspace. Explanation enough, or should I repeat it in words of less than one syllable?’
‘With the subspace boundaries out of phase, we can recalibrate the stunnel transjector and go underneath the jamming field. And the data that we got when you entered our earlier stunnel attempt will tell us exactly what energy levels to use. At least, that’s the plan.’

Type IV Multiverse

I could give more examples of different physical laws in this section, like the energy universe from Counter-Measures, but I don't think I need to.

A Brief Explanation/The Very Fabric of Space-Time

In Vortex Butterflies, it's explained that the course of time is erratic, moving across every dimension and direction (up, down, sideways, and backwards) at once. When the Earth's probabilities were disrupted in 4-Dimensional Vistas, The Doctor kept getting shunted sideways to a universe that was previously just beyond the 'temporal field' of the others.

The concept of parallel/alternate universes are first introduced in Inferno, in which The Doctor's console arrives in a parallel universe by moving sideways in time.

DOCTOR: I came here on my own. I came by accident. I came here. The Tardis console slipped me sideways in time. Slipped me sideways in time.

The Face of the Enemy (basically a sequel to Inferno) clarifies that the normal mode of travel for TARDISes is back and forth through time. The author clarifies this in the intention.

‘A parallel space-time continuum,’ the Master said simply, ‘occupying the same space-time co-ordinates as this Earth, but in a different dimension. Sideways in time, if you like, rather than forward or back.’ Benton scratched his head. ‘You mean some sort of mirror universe, like in that Star Trek episode when Spock had a beard?’
That contradicts Mawdryn Undead, of course, but I’ve always felt that, since the Doctor had to slip the TARDIS sideways in that story to escape the warpellipse, the Earth-based sections of that story were set in some parallel universe.

For context, the reason pre-Time War TARDISes (despite having the ability to breech the fabric) don't normally travel into alternate universes is because they have protections in place. The Lost Dimension even directly touches upon this, with the earliest true TARDIS being shunted into the Void because it didn't have dimension buffers.

TARDISes from before the end of the Time War are powered by an internal Eye of Harmony and receive the majority of their power from the Eye on Gallifrey. When a TARDIS travelled to a parallel reality before, it'd play havoc with the TARDIS' power systems due to being beyond the Time Lords' noosphere, but the TARDIS would still be operational.

Once, at the dawn of the first age of the Time Lords, Rassilon had decreed that all Gallifreyan technology would be powered by the Eye that lay buried below the Panopticon as a symbol of the might of the Time Lords. However, over the subsequent millennia, it had become clear that this was both inefficient and potentially dangerous: missions to the edge of the Time Lord noosphere ran the risk of drifting beyond the range of the eye. Despite protests that it was blasphemous, all TARDISes later than Type 25s carried perfect block-transfer computations of the prime Eye.

However, following the Last Great Time War, the walls between realities were closed off. Travelling through reality is virtually impossible, reduces even the internal Eye of Harmony of TARDISes to a powerless state, and requires enough power to break through the walls of reality.

DOCTOR: Not in the real world. It used to be easy. When the Time Lords kept their eye on everything, you could hop between realities, home in time for tea. Then they died, and took it all with them. The walls of reality closed, the worlds were sealed. Everything became that bit less kind.

DOCTOR: But when it made the hole, it cracked the world around it. The entire surface of this dimension splintered. And that's how the ghosts get through. That's how they get everywhere. They're bleeding through the fault lines. Walking from their world, across the Void, and into yours, with the human race hoping and wishing and helping them along. But too many ghosts, and

DOCTOR: Then the Cybermen travelled across, then you lot. Those discs. Every time you jump from one reality to another, you rip a hole in the universe. This planet is starting to boil. Keep going and both worlds will fall into the Void.

But that's not to say time doesn't travel through realities, since parallel universes are still being created.

Characters can travel through the Very Fabric of Time (located in the threads, aka possibilities, of time) by using shears to cut it. Notably, while they do cut holes in the fabric, they still explicitly use it rather than simply exiting the fabric.

Coward nodded. ‘These are what I use to slash open the Very Fabric of Time and Space. As fabrics go, it cuts and slices open rather beautifully. ’With that, and with no further ado, N ̈oel held up his hand and gave the air in front of him and decisive pinch and a tweak. The empty air seemed to shimmer and ruffle before their very noses. Then he plunged the open, jagged-edged shears into the wrinkle in the air and he started to cut. There was a delicate tearing noise, like blades running neatly through the finest damask. The Doctor and Char watched him make his careful gash through the Very Fabric of Time and Space. ‘We have an appointment, the three of us,’ said Coward lightly. ‘We have to leave Mayfair in Wartime.’ ‘We do?’ said the Doctor. ‘Would you care to tell us where we’re going?’ He tried to peer through the hole that N ̈oel had made in the Fabric. The Doctor’s whole body was rigid with tension. ‘In the LA hills,’ said N ̈oel. ‘Into 1978. There is a situation there, urgently requiring our attention.’
They all whirled around then, to see that a fissure had opened up in the Very Fabric of Time and Space.
His body seemed to stretch, warp and fold in on itself. Anji blinked and realised it was happening to all of them. N ̈oel winked at her reassuringly. ‘But where is this?’ she asked. ‘The vortex? ’N ̈oel shook his head. ‘We’re in the warp and the weft of the Very Fabric. A much subtler place than the vortex. Being in the vortex. . . well, that’s just like being on the M25, or something. No, we’re between the Very Threads. . . ’The Doctor looked miffed at Coward’s slight to the vortex: it had become his ostensible home. - Mad Dogs and Englishmen

Iris and her cohorts were using shears to cut through the Fabric and traverse alternate realities by moving sideways. They can go forward and back between certain realities, so the fabric does extend between other realities.

‘Ancient object. Most deadly. Shears through the Very Fabric of Space and Time. Heinous in the wrong hands. Which it currently is.’ She dinged the bell. ‘All aboard! Good! We’re off!’
As Iris would say: one of the reasons the Blithe Pinking Shears were so dangerous was that once they cut into the Fabric of Space and Time, nothing would mend it perfectly again. The damage was permanent and the darkness would always be plain to anyone looking for it.
‘It happened. In this dimension. Transdimensional, I said, remember? Alternate realities. That’s what this is all about.’
He smiled wryly. ‘I thought I knew that, yes. You’re right murmur. Of course they didn’t. So... we’ve stepped sideways into alternate time. Very interesting murmur. Anyway. I’ve got a little job to do here, if you don’t mind.’ He snapped his fingers. ‘Missy? Will you come with me murmur murmur?’ - Enter Wildthyme

Number of Universes

As can be seen throughout the thread (particularly The Ocean of Time - Fixed Points), Doctor Who is based on the many worlds interpretation; parallel universes diverge from the causal nexus along time tracks when moments of possibilities exist.

Setting aside the sheer number of sources that claim there's an infinite number of universes (as these will be littered throughout the thread), there's some contention about the number of parallel universes in Doctor Who, like Inferno and Army of Ghosts.

DOCTOR: The space between dimensions. There's all sorts of realities around us, different dimensions, billions of parallel universes all stacked up against each other. The Void is the space in between, containing absolutely nothing. Imagine that. Nothing. No light, no dark, no up, no down, no life, no time. Without end. My people called it the Void. The Eternals call it the Howling. But some people call it Hell.

DOCTOR: Yes, of course, of course. An infinity of universes, ergo an infinite number of choices. So free will is not an illusion after all. The pattern can be changed.

However, the most recent guide says there should be infinite. Also, both Fire and Brimstone and The End of the Line also alternate between millions, billions and infinite. So, I think it's more likely that it's not an inconsistency, rather just an attempt to rationalise the impossibly vast multiverse.

There are also sources like Spiral Scratch and Auld Morality (see Marc Platt's Cosmology & The Music of the Spheres) that claim the multiverse is not only infinite, but expands exponentially.

Of course, in a multiverse that expands exponentially and is unfixed and infinite in nature, a ‘centre’ is a theoretical and practical impossibility.
I discovered Rummas was trying to stop me, all the Lampreys throughout the multiverse, and so I opted to stop him.’ An infinite number of Rummases in an infinite number of universes,’ the Doctor said (not that Sir Bertrand understood a word, and yet there was something...). ‘You do realise that’s an impossible mission, don’t you?’
All the people commemorated have contributed to history in some way. For every famous scientist, architect or doctor, there are thousands of non-famous people who nevertheless made others happy and content, ultimately becoming the great-great-grandparents of someone who would contribute to finding a cure for syphilis, heart disease or cancer. Or maybe they were the types of people who turned left rather than right one morning and so didn’t run over the five-year-old playing with his football who went on to discover the gene that causes Alzheimer’s, or become a famous sports star and got his team together to raise millions for a disaster charity operating in Shanghai. Or perhaps that little boy became a road sweeper who found a puppy abandoned in a bag, or was an accountant who learned that his boss was defrauding the banks or became a shop owner who refused to sell fireworks to a group of ten-year-olds and thus ensured they never lost eyes or limbs in a potential Fireworks Day disaster. Such are the vagaries of the twists and turns of time; the element of chance that with each breath, with every decision taken, creates ripples that cause timelines to go left rather than right. And thus each person who dies and is buried in one of the countless cemeteries all over the world is responsible, in theory, for birthing equally countless parallel realities, all due to them going left rather than right.

Which is supported by what I said about Daybreak and Vortex Butterflies/Spiral Staircase (see The Ocean of Time).

In fact, The Brakespeare Voyage asserts that certain numbers are relative because the mathematics of numbering parallel universes contains several high order infinities.

Many (perhaps most of these) rejoin the main anchored universe as their micro-changes fall away into quantum uncertainty. When the million sloths are dead and decomposing, what effect will the colour of one hair have had? A few (the mathematics contains several high order infinities, so the number itself may be high) do not appear to rejoin, either eternally leading outside the ‘time-space’ horizon approachable by a normal time-ship, or curving back in closed loops longer than our normal ships can reach, beyond the futures we can access.

Time and Distance/Thin Time

The Doctor states that different universes / dimensions can have different laws of nature and physics. For example, time in some universes doesn't progress linearly, meaning plans can be completed before the planning stage.

Different parallel universes run ahead of other ones in time, with all the universes that Rose hopped to dying at different intervals.

DOCTOR: Rose, you've been in a parallel world. That world's running ahead of this universe. You've seen the future. What was it?
ROSE: It's the darkness.
DONNA: The stars were going out.
ROSE: One by one. We looked up at the sky and they were just dying. Basically, we've been building this, er, this travel machine, this, this er, dimension cannon, so I could. Well, so I could - Turn Left

Three years also passed in Pete's universe and (relative to the Cybermen's perspective) the Void, while practically none passed in N-Space. This is in spite of the fact that dimension cannons are dimension hopping technology, not time travel technology.

PETE: And the debate went on. But all that time, the Cybermen made plans. Infiltrated this version of Torchwood, mapped themselves onto your world, and then vanished.
DOCTOR: When was this?
PETE: Three years ago.
DOCTOR: It's taken them three years to cross the void, but we can pop to and fro in a second. Must be the sheer mass of five million Cybermen crossing all at once. - Doomsday

In Time In Office, The Doctor futilely attempts to slip sideways into a parallel universe where time runs opposite in order to avoid a Vortex Manipulator.

Some parallel universes mere nanometres and milliseconds apart, while others are far removed.

‘It’s true that alternative universes can exist in parallel with each other, separated only by a millisecond of time and a nanometre of space, without ever having any contact. But there is a danger, at the point of divergence, that one reality will wipe out another instead of splitting from it cleanly. If that happens you probably won’t have been at Brendon where we met, or on Earth at all. Your personal timeline would be rewritten. Possibly for the better... possibly not.’ - Imperial Moon

The Scientific Secrets of Doctor Who/Arthur's Dimension

The Scientific Secrets of Doctor Who claims that the Doctor Who is a Type IV multiverse. The example it uses is Arthur's universe from Battlefield.

In 2003, physicist Max Tegmark suggested that there might be four different types of multiverse. The first, a Level I Multiverse, is anywhere in our universe further than 46 billion light years from Earth. That distance is the furthest that we can see into the universe, so anything beyond it is effectively cut off from us. In Level II, our entire universe is just one of a number of distinct bubbles inside a greater whole – like E-Space and N-Space in Doctor Who. In Level III, there are universes for ‘every conceivable way that the world could be’ – universes branching out from each other as choices lead to different outcomes, such as Schrödinger’s dead and alive cats or the consequences of Donna’s choice to turn left or right in Turn Left (2008), which we’ll discuss more in Chapter 6. Lastly, in Level IV universes, even the laws of physics can be different and anything might happen. In Battlefield (1989), the Doctor says the Arthurian knights come from ‘another dimension’ and ‘sideways in time from another universe’ – one where magic seems to be real. That suggests the other Earth where King Arthur is real has its own laws of physics, different to our own. If all possibilities are played out somewhere, then there’s a universe where Doctor Who is real – all of it, even the bits that are contradictory or silly – and another universe where you are the Doctor, and another where you’re a Dalek. Perhaps there are even more than these four levels of universe. In 2011, physicist Brian Greene suggested nine different types. There might be many more. It’s ironic, isn’t it? Trying to understand the very smallest size of matter has led to fundamental questions about how the universe works at the very biggest scale.

And its claim isn't entirely inaccurate. Arthur's dimension is an alternate universe that's sideways in time, and can be accessed through an interstitial vortex.

DOCTOR: Earth. Rippling out through the cosmos, forward in time, backwards in time and sideways in time.
ACE: Sideways in time?
DOCTOR: Yes, sideways in time, across the boundaries that divide one universe from another.

ACE: Where does Ancelyn come from?
DOCTOR: Another dimension. Sideways in time from another universe.

DOCTOR: At the other end of that interstitial vortex.

Initially, I dismissed this for three reasons; firstly, there weren't other examples that I could find at the time. Secondly, the story doesn't necessarily suggest it's actual magic, just that it's at least an advanced form of science. Lastly, there's also some fuckery about Arthur's world in a few older stories, so that's why I've been looking into other examples.

ACE: Ask a stupid question. Well, if they're grown, how do they fly?
DOCTOR: Magic.
ACE: Oh, be feasible, Professor.
DOCTOR: What is Clarke's law?
ACE: Any advanced form of technology is indistinguishable from magic.
DOCTOR: Well, the reverse is true.
ACE: Any advanced form of magic is indistinguishable from technology?

However, the most recent depiction of Battlefield from The Monster Vault confirms that magic is the dominant force.

Gateways

Gateways formed from CVEs can access non-euclidean geometries. Since Adric specifies 'other quantum states', this also implies that N-Space (Minkowski Space) is a quantum state like the dimensions Gateways connect to.

‘I recognize some of that equipment,’ Adric realized. ‘I saw it in the Scientifica; It was a research programme into–’ he racked his brains ‘– dimensional energy. The Doctor said it was a dimensional observatory.’ ‘Meaning what, exactly?’ ‘It allows them to look into other dimensions,’ Adric explained. ‘Perhaps that’s another Gateway.’ She looked away from the Machine for the first time ‘A what?’ ‘At the mathematical boundary of E-Space and N-Space the Doctor found a pan-dimensional structure that allowed transference between Minkowski Space to other quantum states, access to non-Euclidean geometries, post mathematic spatio-temporal co-ordinates and extra universal–’ ‘Yah, OK, I get the message: inside that thing you think there’s a doorway to another dimension.’ ‘Yes. Or perhaps just to another universe.’ - Cold Fusion

Bubble and Brane Cosmology/Wildthyme in Purple/Expanding Universes

If Doctor Who universes are supposed to be bubbles, then why are there enough examples of multiversal brane cosmology to make poems about it?

The answer is simple: both. I'll just post the full quote from The Brakespeare Voyage here.

Parallel worlds are based on the same laws of physics as N-Space, but diverge at crucial moments. Parts of the multiverse 'Otherward' to the parallel worlds, which are so far out that timeships go insane and die, are bundles of universes collected in branes with different laws of physics. Additionally, there's failed universes where gravity is too strong, stars age too quickly, etc.

Think of the universe for a moment as having three additional directions (alterward, paraward, and otherward) all at right angles to the ones you know (length, breadth, width and time). This is a tremendous oversimplification, but it may help. Paraward, we find a sheath of histories which are either eternally separate from our own anchored time or which diverge and return to it so far in the past, or so far in the future, as to be – functionally – eternally separate from it in terms of the noospheres of the Great Houses. The physical laws of these universes are identical to ours, but all else is different. We call these paraward space-time entities ‘parallel worlds’. Alterward, we find those histories which divert, at crucial or innocuous moments alike, from ours. Here are the worlds where a toe goes unstubbed, or a vital battle is lost, where the five hundred and eleventh hair on a sloth in the forest has gone grey in one world, and white in another. Many (perhaps most of these) rejoin the main anchored universe as their micro-changes fall away into quantum uncertainty. When the million sloths are dead and decomposing, what effect will the colour of one hair have had? A few (the mathematics contains several high order infinities, so the number itself may be high) do not appear to rejoin, either eternally leading outside the ‘time-space’ horizon approachable by a normal time-ship, or curving back in closed loops longer than our normal ships can reach, beyond the futures we can access. We call these alterward space-time entities ‘alternate worlds’. Perhaps paraward is just a way of talking about extreme alternates, and alterward is just a way of talking about probability bundle universes. But then there is Otherward. Otherward is Outside To Otherward the laws themselves are different, the biodata is constituted from other principles. These are universes held on separate ‘branes’ in hyperspace, outside the sheath that contains the paraward and alterward components of our universe. These are beyond the reach of our time-ships, who go mad in the horrors of the void between. As The Brakespeare eases itself out of our reality, using the engineered rupture of the Great Attractor as its point of exit, the ship’s flank – all million worlds of it, all two thousand years of it – encounters Otherness in one sweeping surge. Instantly (to us here on the Bridge) the history the ship is built out of begins to warp and creak ominously, like the timbers of a long becalmed ship putting into a stormy sea. Instantly, we harvest two thousand years of toil and sweat and strangeness. First we weather the impact of the minor ‘failed’ universes that cluster around ours. Failures only in terms of our own expectations, built into our arrogance, that a ‘functionally’ correct universe will produce and support complex cultures like our own. In most of these dwarf-universes, gravity is too strong, stars age too quickly, even faster chemistries cannot cope when complex second-generation elements die unborn in the hearts of first-generation stars whose lifetimes pass in periods measured in tens of thousands of years. Along The Brakespeare’s starboard worlds, we begin and end the harvesting of these brief stars. They will feed the timeengines that drive data and craft up the spine of the ship, to the Bridge.
The single lone Brakespeare, shorn and denuded of its sheath of space-time by some accident or horror we could not guess at, a naked skeleton of worlds, tormented into flat surfaces of bone like an immense flattened fossil, solidifying under the pressure of geological ages. Perhaps it had been caught between colliding branes: destroyed by the creation of two other universes.

Wildthyme in Purple outright states the multiverse is a Type IV ('Tegmark') brane cosmology, in which metafiction/fiction exist.

Axel concluded his performance in time for me to catch the tail end of the two physicists’ conversation. “… Tegmark’s classification of multiple universes shows that there are planes of existence beyond our cosmological horizon, with different physical laws, different languages, rules...” the big physicist was in full flow. “Oh, there are? Of course there are. And who’s to say that fictional creations in one universe can’t be real in another? No child over six, anyway.” “One day you’ll learn to think–” “One day you’ll come up with a better description of current reality than a… a… series of universal planes collapsing in a… meta-fictional Big Crunch–”
“One day you’ll come up with a better description of current reality than a… a… series of universal planes collapsing in a… meta-fictional Big Crunch–” “–Big ‘Brane Crunch–” “–really Ed? That sounds like a breakfast cereal. Anyway, whatever it’s called, clearly it needs a better name. Then we can all have tea and cake while the Marx Brothers and Rod Serling plan the marketing campaign.”
As the members of the Court scurried to scoop up the stray fish and find them new homes the big physicist said, “There you are, you see, that’s just what I was afraid of. The damn idiot pushed the damn button. He’s using the seetee bombs, trying to remove enough meta-mass to prevent the Big ‘Brane Crunch. But he’s wrong. When you remove fiction all you’re left with is non-fiction. We’ll see the effects soon enough, and frankly I’m not looking forward to it. Fiction and non-fiction planes will react like matter and anti-matter. Total annihilation. A meta-reality tar-pit deep enough to un-make the entire multiverse. Not only will nothing have ever existed – it will never have existed forever.”
"Kinky bugger." She shook her head, as though clearing away an unwelcome image. "Anyway, the inspiration for the fictional version was given to Johnston McCulley, sort of metaphysically slipped into his drink so he'd write Zorro into the realities that he didn't exist in, and make the legend last. He screwed it up good and proper though. Gave it an ending where Zorro retires. In the first story! Legends can't buggering well end! They lose half their power if they do that."
The Doctor's Wife

The Doctor's Wife strongly implies that it's more complicated than simply bubble and braie.

RORY: How we can we be outside the universe? The universe is everything.
DOCTOR: Imagine a great big soap bubble with one of those tiny little bubbles on the outside.
RORY: Okay.
DOCTOR: Well, it's nothing like that. Completely drained. Look at her.
AMY: Wait. So we're in a tiny bubble universe, sticking to the side of the bigger bubble universe?
DOCTOR: Yeah. No. But if it helps, yes. This place is full of rift energy. She'll probably refuel just by being here. Now, this place. What do we think, eh? Gravity's almost Earth normal, air's breathable, but it smells like
The Quantum Archangel

The Quantum Archangel also shares some similarities with The Brakespeare Voyage, with universes starting small and mostly reabsorbing into their primary probability thread. For full context, it's clarified later that complete parallel realities diverging too quickly are the problem that Chronovores solve, which is why there's already parallel universes (like the Cla’tac’teth's universe, which was similar to N-Space before its entropy accelerated).

‘Imagine the multiverse – the totality of all possible universes – as a garden. The multiverse has to be tended, nurtured... and pruned. Parallel universes are a fact of life – quantum uncertainties lead to Jonbar hinges and then the universe diverges, buds. But the overwhelming majority of these buds rapidly rejoin their primary universe, nanoseconds later. However, there are occasions when buds diverge from that primary reality very quickly. They possess enough dimensional momentum to achieve escape velocity – they become important. ‘These parallel universes branching off from the primary are considered to be weeds in the garden, an infestation that must be cleared.’ ‘Why?’ asked Mel. ‘Remember, I’m the only nontemporal scientist in the room, Doctor. What harm do they do? It’s not as if they’re going to run out of space, is it?’ A good point – and Arlene was a temporal scientist. She could just about remember listening to Stuart’s entertaining lectures about parallel universes. Except that they had been Ruth’s lecture, hadn’t they? The Doctor smiled warmly at Mel. ‘No, but there appears to be a possibility that they will run out of reality.’ He held up his hands. ‘And I’m not sure how or why, either. But these parallel realities are considered to be a threat, and, like weeds, they are pruned, weeded out. ‘And the Chronovores are the gardeners.’
‘But the truth is, the Earth is now teeming with probabilistic effects, inverted causalities and the beginnings of complete parallel realities.’
The Cla’tac’teth is an insectoid race that will live just before the heat death of the universe. Their home is a neutron star orbiting the Great Attractor.’
The Master forced himself to stand upright. That will not be an issue, Doctor. We will only be in the parallel universe of the Cla’tac’teth for the briefest of moments. But it will offer us a short cut to the Great Attractor in this universe, and the chance to stop this Archangel gestalt from assimilating it.’
The logic might hold together, but the Doctor still didn’t like it. Chronovores or not, parallel universes were nasty things and did nasty things to TARDISes. But unfortunately, their options were limited and their time was short. Once again, he found himself facing the most uncomfortable of decisions: no choice.
The Macros

The Macros also follows a somewhat similar throughline. Universes start out as micro-continuums, and grow and multiply.

DOCTOR: It is a bit complicated. Look, parallel universes multiply at an unimaginable rate. Every moment in time, something happens that generates another alternative dimension. Nature has to cope. Somewhere, all these divergent universes have to find their own space. And endless and timeless as the universes may be, the multiplying dimensions have to have space. The way this happens is that each division becomes a micro-universe in the macro-universe that spawned it. So, the universe we're in at the moment is just a micro-universe in another macro. Are you following me?
YKA: It's quite incredible.
EZZ: How does that make it possible for this battery to energise our dimension in perpetuity?
DOCTOR: It's all to do with size. Your dimension uses a minute amount of energy, compared with this dimension.

DOCTOR: Time runs differently in your dimension. It passes more quickly. Each time we travel between our world and yours, and vice versa, I have to individually adjust the temporal stream of anyone inside the Tardis. Peri would have been all right if I'd been able to calibrate her body to the local time scale. Instead, she's suffering from a kind of lethal jet lag, and we really haven't a moment to lose. Quickly, in here.

TESSLER: I'm still finding what you said hard to swallow, Doctor. I could have just about accepted that we've been here for six months, but six decades?
DOCTOR: As I said, time here is largely irrelevant. The good news is that you're not trapped in a loop like most of the crew. But you have been affected by the fact that the ship is suspended between two different time dimensions. Sixty years passed by for you as though it was just a few weeks.

Finally, there's Short Trips: Monsters - From Eternity, where it's stated that universes are contained in higher dimensional membranes to expand infinitely.

I was not alone! I was not even dying. I screamed, I sang, every part of me altered now, bursting with new life and energy. Truth came then, and with it an understanding I could never grasp while bound by a single universe. The truth: that there are many universes, each one expanding endlessly within its own higher dimensional membrane. That the ‘branes move within a still larger space, in directions I could never previously conceive. Colliding, potential existing within the ‘branes releases energy. Singularities give birth to universes, each cradled in its own eternity of time. At the end of such a universe, I am born. I believe I am alone forever. But I do not yet comprehend what forever is. Other universes mean other Minds. Other Minds like me. An infinity of Others, living and touching, if briefly and infrequently, for eternity. The ‘branes approach, touch, part, leaving new singularities kindled where only potential had previously existed. In a space of time without measure, the moment of destruction inverts.

Checks and Balances

Frankly, I feel we can just write The Coming of the Terraphiles off entirely.

The multiverse is a near/quasi-infinite collection of space-time continuums that follows the many-worlds interpretation.

The Doctor ran his fingers through his hair as he considered this. 'There are people who can use that energy to travel at millions of miles an hour in vessels which can dodge in and out of the different planes, moving between the near-infinite worlds of the multiverse and somehow navigating in order to take a kind of shortcut.
The Doctor proudly told them that dear old Robin 'Bingo' Lockesley had saved Creation, good and bad, sweet and sour, ugly and beautiful, the whole of it from the centre to the Rim, top to bottom, side to side. In short, the quasi-infinite was no longer under threat of an early death and/or transfiguration.
'So how do I do it? How do I get us out of one space-time continuum and into another?'
The pirates, drawn from a hundred worlds and a dozen space-time continua, have come at last.
Out near the Sagittarius Schwarzschild Radius, a storm was brewing, created by forces which had always been there but were now growing increasingly less stable as they shifted in and out of their own space-time continua, making a very dangerous place in which to know perfect bliss.
Only a few were blessed or damned with the Doctor's power to see the multiverse in all its vast, beautiful, bountiful, exotically coloured aspects, its glamouring glory. Those few knew how many truths could exist at once: the countless alternatives, the infinity of paradoxes, the billion twists of fate. That power only came with an understanding of how space could be a dimension of time, still hard for the average head to handle.

All universes and the multiverse itself exist in a state of metaphysical equilibrium that undergoes a cycle of change and rebirth. These include concepts like matter and anti-matter, good and evil, chaos and order, etc.

Amy had picked up a little about the antimatter universe from the Doctor, and they'd met an old philosophical jummybug on Latest Io who had explained to her about Law and Chaos; how the universe maintained stability and creativity, balancing between Law on the one hand and Chaos on the other. But they were not the same thing. Professor Ormic, the learned jummybug, had given the impression that philosophically he saw their universe not in terms of good and evil, but in terms of the fundamentals of the multiverse. Law and Chaos - order and creativity - matter and antimatter were qualities which became good or evil depending on their context.
He'd already told her that only in those spaces lying between the twin planes of matter and antimatter, Law and Chaos, was this war understood and exploited in full.
The Arrow of Artemis. The Roogalator. The beam intended to rest on the fulcrum of the Cosmic Balance.
'Um. Not really.' Amy wasn't quite sure where to start, but she took a deep breath and asked: 'What's matter and antimatter? How do they work?' 'Look at this - my bow tie. The central knot's the black hole. This side of the triangular bow is matter. This other side is antimatter. They are self-perpetuating, like Law and Chaos. Same thing, see?'
'When t'Roogalator were pinched,' muttered Captain Abberley. 'Some damned fool got in there - don't ask how- and stole that beam from the fulcrum which regulates theGreat Balance. I'll thank thee not to ask me, because I can't explain it. But that's t'form it takes for us.'
'Exactly so, Doctor. In other words, my dear, destroy us and you destroy yourselves. Here -' He/they held up his/their hand so that his/their sleeves fell back, revealing his/their skin with its strange pewter-coloured radiance. 'That's what antimatter looks like when it's controlled by the power of Law.' 'Law?' Amy was outraged. 'Law? You think putting on a circus ringmaster's uniform and invading a peaceful ship in deep space is legal?' 'I'm referring, Missy, to a higher form of Law. To the highest form of Law which counters the kind of Chaos your master so enjoys spreading through the cosmos.'
'Because this isn't just physics we're talking about.' The Doctor's eyes gleamed with fascinated curiosity. 'It's metaphysics. It's the only way we can understand reality. And both are represented by mythology, by legends, by the shamanistic power of humanity to tell a story that is an absolute lie beneath which hides an absolute truth. Life and Death, Law and Chaos, Matter and Antimatter. What a species! A poem creates a formula. A formula becomes material. And so it goes on. And now one of us must do his duty.'
In balance, Professor Ormic had told her, these qualities kept the multiverse from becoming too rigidly organised or too disorganised. Constant regeneration. There had always been people of quite disparate origins who dedicated their lives to maintaining the status quo, explained the professor. In the history of the cosmos the balance tilted sometimes one way, sometimes another. The Time Lords had once helped to maintain that balance. The professor pointed out that what he called the Cosmic Balance was a symbolic construct for something enormously complex. He could have told her more, but the maths would have been overwhelming. The Balance was the way in which the multiverse maintained its equilibrium so that neither side tilted too far in one direction or another, since these were the two more or less equal forces which kept the multiverse from collapsing into nothingness. Matter and antimatter were not the same as Law and Chaos, of course. Law and Chaos existed in both spheres.
'Right. Not that kind. Even Time Lords couldn't recall everything from a former existence. I certainly can't. Anyway, that's the fundamentals of life and regeneration in the multiverse. It's a fine equilibrium, regulated by what some people call the Balance, a semi-abstract visualisation which can be said to act like the beam, fulcrum and pans on an ordinary pair of old-fashioned scales to maintain everything in equilibrium.'
'Well, to put it as simply as I can, somehow, through interference by something or somebody, the process of regeneration has been speeded up. Speeded up so much that parts of the process have not had a chance to develop and degenerate and therefore re generate naturally. It feels as if the Balance has been pulled apart. Instead of expanding and contracting, as it should, the multiverse has gone out of kilter. These storms are partly the result of antimatter "infecting" matter. Matter is corrupting antimatter. Law is infecting Chaos, and Chaos is infecting Law. We need to find out why. And we have to restore the Balance, otherwise the entire cosmos will become infected until it rapidly degenerates and collapses into inchoate matter - nothingness. The conquest of Death over Life. Anything remaining sensate long enough to witness this process would live that moment of dying for ever!'
'Because Miggea is the only "rogue system" that still exists in the multiverse. Miggea is able to move in an eccentric orbit which passes through all aspects of reality somehow without being destroyed. If, while we're in that system, we can - I don't know - re-adjust the cosmos, restore the Balance, then we stand a chance of surviving. Of everything surviving. That system's as far as you get until you come directly under the influence of the black hole.'
'Intelligence, Doctor. There's the key, eh? It would cease to be. Whatever you call that fundamental power of reason and creation is what allows the multiverse to exist. Without it we are condemned, essentially, to non-existence. Whatever our motives or ambitions, they are meaningless without an ordered multiverse where Law balances Chaos, matter balances antimatter, Life balances Death. One cannot exist without the other. And somehow, as you've observed, antimatter is infecting matter, Law and Chaos are confused and soon - what?' 'Life and death will become indistinguishable. Matter and antimatter, law and chaos, good and evil, become indistinguishable. All the opposing qualities which at present are in balance, which give meaning to existence, will disappear.'
'Now, what if the balance, on which we depend, were maintained by something more than a metaphysical idea but by a physical element? Let's call that element a "regulator" the same sort of thing they put on primitive beam engine to make them work at a desired speed and so on. Clocks too. This regulator maintains the multiverse theoretical through eternity. The universe of matter slowly become antimatter and the universe of antimatter turns into matter. Out of death comes life and out of life comes death. Opposite sustain existence.'
They would all remember when, looking up into the sky where a black sun burned, they saw a long slender silver lance slide into the place where the Balances wayed, between Law and Chaos, Love and Hate and all the other opposing forces that determined the existence of Creation. And, back in place at last, that good old Roogalator, the regulator of the great engine of space and time and of all the various abstracts which, thanks to our love of myth, so quickly become actualities, resumed its steady movement. The black tides no longer raced through the universe. Shadowy harlequins and pierrots no longer danced upon the ruins of countless realities. The multiverse could return to its stately natural cycle.

Affecting the balance of any one universe affects the whole multiverse because actions echo to infinity.

She understood that it had something to do with self-similarity. Her actions affected every aspect of the multiverse, were echoed on every plane, every alternative. Whatever danger threatened them now would threaten them everywhere. These other universes were no more independent of the presence to which they were drawn than her Earth was independent of the sun. It had nothing to do with size. If she pushed, the whole multiverse responded. If she slept in this aspect of herself then she probably slept in all other aspects. And how many were there? Millions? Billions? Probably. But was this also true of the Doctor who she could see now doing something with his sonic screwdriver? The ship divided and became many ships, each one a fraction bigger than the next. Each one containing an Amy, but not a Doctor. Where was he? Was he independent of the multiverse? The only one of his kind?
How could you take yourself and your own desires and ambitions seriously? Amy wanted to know. How could you expect to have any effect at all on major events? Then she shrugged as she had often shrugged before. The answer was, of course, very simple: in spite of your being so apparently insignificant, every action you or any other being took in the multiverse had meaning and effect, and was echoed in every other version of reality. Everyone was their own multiverse, just as the peak of Everest contained fragments that were models of the whole.
'But you said our actions were echoed over and over again as if to infinity.' 'But by us. I'm not sure. There are people who take the same actions, fulfil, if you like, the same destinies. Everywhere, throughout the multiverse there are people like us trying to put things right or sometimes just trying to stop things getting any worse - echoes of echoes, shadows of shadows. Call some archetypes. Jung did. But maybe we're all archetypes. Maybe there's no such thing as an original? Maybe the multiverse has no original. The World Snake eats its own tail. No beginning and no end.' He looked into her eyes. He grinned. 'We carry on for ever. Paradox upon paradox.'

Sagittarius A is a gateway into the antimatter side of the multiverse. This is because it's simply an aspect of a more massive, denser black hole that exists at the centre of every universe in the multiverse.

Scientists in his home galaxy first noticed it. That each galaxy had a black hole into which matter was pulled had been understood for centuries. People had also known that their galaxy was in turn being drawn towards an even stronger source of gravity.
'We're looking through the Sagittarian Schwarzschild Radius from the perspective of the Second Aether,' explained the Doctor. 'I doubt if it would be possible for people like us to do this under any other circumstances. The heart of it down there is the black hole which represents the centre of our multiverse and all black holes and universes everywhere to quasi-infinity, although there is, paradoxically, no centre to the multiverse and yet countless centres. But that's what began to go wrong millennia ago...'
Cornelius knows that whatever it is which lies at the centre of the universe, what we call a super-black hole, something unimaginably dense and tinier than an atom, has become erratic: the very thing which provided balance to the universe was now unbalancing it.
In our own galaxy our black hole is the best-known gateway into the antimatter multiverse, which exists in opposition to our own. It is, I believe, one of a series orbiting that larger phenomenon. Opposition is what guarantees the survival of everything in Creation. Without it the multiverse would collapse into inchoate primal matter and antimatter which in turn would dissipate into nothingness - a multiverse without shape or meaning - or intelligence.'
From what she could tell he was worried about some bad guys called General Frank/Freddie Force and his Antimatter Men, who had ventured over to our side of a super-dense black hole in Sagittarius. They had been there in the far, far future for some time, apparently, and their malign influence was spreading backwards to the here-and-now. 'Up to their old-fashioned dirty work,' the Doctor said, 'those Antimatter Men. Dipping in and out of the "Second Aether". And my guess is they're probably not the only ones.' He chewed thoughtfully on his pop-tart. 'Someone's messing with the normal rules of energy flow. Time and space are all over the place. Quite literally, I mean. Growing increasingly unstable.'
'We're looking through the Sagittarian Schwarzschild Radius from the perspective of the Second Aether,' explained the Doctor. 'I doubt if it would be possible for people like us to do this under any other circumstances. The heart of it down there is the black hole which represents the centre of our multiverse and all black holes and universes everywhere to quasi-infinity, although there is, paradoxically, no centre to the multiverse and yet countless centres. But that's what began to go wrong millennia ago...'
As far as I know, this is the first time he's risked coming so far away from that blackhole. That hole is the core of our universe, as an even denser one exists for the whole multiverse. Both lie at the centre of our universe and Frank/Freddie Force's antimatter universe.
She was big. An undine as big as the universe and able to see galaxy after galaxy after galaxy all streaming towards an invisible source of gravity. A supermassive, infinitely tiny presence, smaller and heavier than any black hole at the centre of any single galaxy. She realised this presence was the nucleus and everything else was moving according to its extraordinary density, its immeasurable gravity.
'We're actually orbiting the black hole. We've no business existing, yet we do exist. I don't know how time relates to space here. Not really. Especially where gravity's an important part of the equation. But this isn't an aberration. I think all aspects of the multiverse have systems like this at their centre. It's part of that grand design, that logic we find so hard to grasp. Wheels within wheels. A quality of gravity that's barely begun to be examined. Gravity within gravity? Like electricity, we know it happens but we don't know how or why. We can learn how to use it because that's what we're good at. Yet - I'm not sure —'

This is consistent with the novel Dominion, which states that black holes can be used as wormholes similar to CVEs.

‘Not quite,’ said the Doctor, wagging a finger at her. ‘Our universe takes its energy from pocket universes, drawing the energy through black holes or Charged Vacuum Emboitements.’
No.’ The Doctor shook his head, walking up to stand beside her. ‘It is –was – a pocket universe. Imagine our universe as a balloon. Now imagine a small section “pinched off” from our universe, through a black hole.’

People exit their universes by using dark tides created by black holes.

Captain Cornelius inspects certain items of treasure, searching for that fabulously valuable ingot of newtonium, puzzles over his data and his charts, confers with Peet Aviv and begins to understand that fear he has always exploited but never until now known. For there are dark tides running through the universe; currents so powerful they drag whole galaxies with them, streaming gravities so strong they swallow light and threaten Captain Cornelius's familiar existence; ultimately they threaten every form of sentient existence and if unchecked will absorb the whole of Creation.
He understands, perhaps more than anyone, that something terrible is happening within the Schwarzschild radius. And what is that unseen, unimaginable power which remorselessly drags this galaxyand thousands of other galaxies towards what must be thecentre of the multiverse. Dark tides ripping and running through the whole of perceived reality.
He laughed. 'I hope not. This is something that wasdiscovered in your own time - roughly - and was used toprove the existence of a largely invisible multiverse. They called those streamers "dark flow". Now they're knownas dark tides. They're moved by gravity, like ocean tides.They seemed to come from nowhere and move at millions of miles an hour, dragging whole galaxies with them. Weare all so delicately, so vulnerably connected.' He shivered. Amomentary chill.
The Doctor ran his fingers through his hair as he considered this. 'There are people who can use that energy to travel at millions of miles an hour in vessels which can dodge in and out of the different planes, moving between the near-infinite worlds of the multiverse and somehow navigating in order to take a kind of shortcut. Really it's mostly an astonishing skill at negotiating the gravitational pull from universes or galaxies within those universes that aren't visible to us. They've been moving away from the centre of our galaxies for at least two and a half billion light years.'
'That the dark tides are certainly running. Leaking intoour hemisphere. Wide and deep. A million currents all atdifferent speeds. Different times. Faster than I realised.Dangerously fast. Way beyond any previously noted speeds.Which essentially means everything will vanish from theuniverse, maybe even the multiverse, long before theirnatural, expected time. A thousand years or less instead ofbillions...'

Omega is basically Doctor Manhattan.

The interior of even pseudo-black holes in Doctor Who are non-places, and falling into one should crush someone into a dimensionless singularity.

CHANCELLOR: That's a nowhere, no place, a void. According to all known laws, nothing can exist there. - The Three Doctors

DOCTOR: Unless we find a way of getting out of here, we're all going to be crushed to a singularity.
TEKA: What's a singularity?
ROMANA: A mathematical point with no dimensions. - The Horns of Nimon

But, through inconsistent means, Omega's sheer force of will allowed him to survive the descent into the pseudo-black hole (see The Ocean of Time - Continuity Note for details), whereas almost anyone else in that situation would've died. He landed in an impossible pocket universe and could impose his will on the black hole's singularity to conjure any antimatter object he desired.

It was only later that the Time Lord known as the Doctor discovered the truth: Omega had survived the experiment, and was now trapped inside a pocket universe formed of antimatter, driven insane by millennia of solitude. Despite his efforts to seek revenge upon those he claimed had abandoned him, he was never able to fully return to the universe of matter, and his own antimatter universe was eventually destroyed. - The Whoniverse
DOCTOR: Yes, exactly. That's where we are. On a stable world in a universe of antimatter. An anomaly within an impossibility.

BENTON: It's not just a matter of the same country, sir. If the Doctor's right, we're not even in the same universe.

TYLER: Look if this is a world of antimatter, how can it all exist?
DOCTORS: The phenomenon of singularity.
TYLER: Singularity?
DOCTOR: Look, you explain to him. You're far better at it than I am.
DOCTOR 2: Oh, no, no, please. Older and wiser head.
TYLER: Singularity. Now I know it's supposed to exist
DOCTOR: Yes, well, it does exist. Right here, I'm afraid.
TYLER: But that's just a theory.
JO: Oh look, Doctors, what are you talking about? And simple answers, please. One at a time this time.
DOCTOR 2: Well, singularity is a point in space time which can exist only inside a black hole. We are in a black hole, in a world of antimatter very close to this point of singularity, where all the known physical laws cease to exist. Now, Omega has got control of singularity and has learned to use the vast forces locked up inside the black hole.

DOCTOR: All this exists because you have willed singularity to create it all for you.

Without him, everything inside the antimatter universe wouldn't exist.

DOCTOR: All this exists because you have willed singularity to create it all for you.
OMEGA: Exactly.

OMEGA: So long as I control singularity, I can make it do my will. All these things exist because I will them to exist. Without me and the unceasing pressure of my will, the work of thousands of years would collapse into chaos in microseconds. I am, if you like, the Atlas of my world.

To clarify, Omega did create all the antimatter that exists in the realm, but it's antimatter in the first place because the realm itself is opposite to the normal universe.

CHANCELLOR: Are you telling me we are up against an adversary, a force, equal to our own?
PRESIDENT: Equal and opposite to our own.
CHANCELLOR: A force which inhabits a universe where by definition even we cannot exist?
PRESIDENT: Yes. A force in the universe of antimatter.

PRESIDENT: Your Excellency, you have said yourself we are dealing with a threat from an area over which even we have no control. A black hole in space. The universe of antimatter. Unknown forces at least equal and opposite to our own.

In K9 and the Time Trap, it's described as a bubble of time where no time passes.

Like The Three Doctors version, Omega's will sustains the anti-matter realm.

‘It isn’t as simple as that. This universe only exists because he wills it. Without his consciousness it would cease to exist.’

It's a full continuum.

Helios turned away, tapping the doors with his staff. ‘Whatever is beyond the doors, it is a power that no man should possess.’ ‘The universe of anti‐matter,’ the Doctor explained as he got to his feet. ‘A spacetime continuum like ours, equal but opposite, reached via a singularity. Normally, if I’d opened the doors, the two universes would have come into contact. There would have been annihilation.’

Both universes are separated by a threshold, regulated by a naked singularity.

I crossed the threshold,’ he said. ‘I passed into another universe. Anti‐matter, regulated by a naked singularity.’ [...] ‘The boundary between the universes of matter and anti‐matter is a source of infinite, self‐sustaining power. A sentient being can harness that power by using the singularity, and bring theories into fact, It literally allows you to do anything you can imagine – uncouple matter and energy, resolve paradoxes, redraft the laws of mathematics and physics.’

As stated in Whotopia, there are multiple anti-matter universes, with Omega's Realm and the Planet of Evil universe being separate domains.

This anti-matter universe exists side-by-side with the known universe. Since Zeta Minor exists on the edge of the universe, it has a link (as in a portal kind of thing) to the anti-matter universe.

VISHINSKY: He has disappeared into the vortex between this universe and the next.

SALAMAR: Yesterday, you were found with the body of one of our scientists. Last night one of our guards died and you were seen kneeling over him. Can you explain this?
DOCTOR: We had nothing to do with those deaths. They were brought about by your intrusion. Listen, now listen to me, please. Here on Zeta Minor is the boundary between existence as you know it and the other universe, which you just don't understand.
VISHINSKY: Other universe?
DOCTOR: Yes. From the beginning of time, it has existed side by side with the known universe. Each is the antithesis of the other. You call it nothing, a word to cover ignorance, then centuries ago scientists invented another word for it. Antimatter, they called it.
SALAMAR: Nonsense. Clever deception to cover their real motives.
VISHINSKY: I don't think so. Let him finish.
DOCTOR: And you, by coming here, have crossed the boundary into that other universe to plunder it. Dangerous.

DOCTOR: No, no. It's tempting to let them go ahead and destroy themselves. The trouble is, they wouldn't be the only ones.
SARAH: How do you mean?
DOCTOR: Cataclysm.
SARAH: The Big Bang?
DOCTOR: Yes. The end of the universe.

In the sequel, Zeta Major, it's stated to be the opposite of matter rather than oppositely charged matter. Coming into contact will cancel them out.

‘I remembered, from before. They helped me. What the Morestrans are doing, collecting anti-matter, is causing a great imbalance both here and on the other side, in their universe.’ ‘Anti-matter?’ asked Tegan. ‘Well, not anti-matter in the way you understand it. Or as the Time Lords understand it. It’s more like a nothingness, a universe utterly opposite to our own. It has existed alongside our universe since time began. In fact, you might be better off thinking of it as “ante-matter”.’
‘Obliteration. Both forces cancelling each other out. The end of everything.’

Everything in this universe is comparatively distorted, including time.

The Doctor smiled, sad for some reason. ‘It’s not as simple as that, Tegan. Don’t you understand? Their universe, it’s so different, so alien, that even Time has a completely different meaning. They cannot stop what they do just like that. They must continue trying to stabilise the breach that these Morestrans are creating. Which means that although I can switch it all off a lot more easily, it’s still there, inside me, growing. Unless I can return the anti-matter, unless the balance is restored, their cry for help is going to kill me.’

In Voyage to the Edge of the Universe, a Fourth Doctor comic from a similar period, it's shown that the edge of the universe is able to access parallel universes, suggesting that this is a parallel universe.

Spiral Yssgaroth

Spiral Yssgaroth is an alter-matter universe (though not an alternate dimension).

In fact, the Yssgaroth were so blatant a force of destruction that it’s questionable whether they really were a species at all. Their source was extra-continuual, but evidently “other universes” are nowhere near as romantic a concept as many people believe. The world of the Yssgaroth wasn’t an “alternate dimension” or a “parallel timeline”, but an alter matter state so alien that its structures and protocols were completely inimical to those of the Spiral Politic. The universe of the Yssgaroth itself seemed to hate the known continuum, which has led to speculation that rather than being a true form of life the Yssgaroth were simply side-effects of the collision between two continuual strata, symptoms of a timeline which had already started ripping chunks out of its own flesh. - The Book of the War

Energy from Spiral Yssgaroth works against the physics of the universe.

“I am,” said Maxie. “The energy emanating from this area has properties that work against the physics of our universe. That suggests whatever we’re dealing with comes from another dimension, so I brought with us every piece of dimensional tech P.R.O.B.E. has. I don’t have to understand which dimension our bad guy is coming from to destabilise the gateway it’s coming through.”
At the centre of the ancient circle, a maelstrom of energy erupted from the crack in the earth. Flashes of green, orange, and white light bathed Archie’s followers as they continued their ritual. They chanted louder as their excitement grew. The Yssgaroth was coming.
Giles looked left to the centre of the circle where the otherworldly energies of the Yssgaroth’s universe poured into their own. Walking towards the maelstrom was Az, unnoticed by the vampires still focused on their ritual. - Out of the Shadows - Preternatural Nights

So how do we know the Yssgaroth are part of the multiverse, and not just part of some random dimension that exists in the Void?

“Be silent and listen, biped. My takeover had to be… postponed, of course. The Clock-People found me. Their leader, Carvil the Resurrected, tried me for interference—what a joke—and I was banished into the same hell they’d escaped. The Void Between Worlds. And there, I met my patron. A being like and unlike myself… from the days before History. They took me under their wing. Taught me what I had to do, my true calling.”

Because Spiral Yssgaroth is separated from N-Space by the Very Fabric of Time and Space, not some sort of buffer zone like the Solitract Plane.

And the Prince’s words were thus: ‘The Mother did lead me through the shadowed wastes of the nether, and showed me the Spiral, the very structure of History stitched and sewn between stars like a tapestry of gold and bronze. She brought me close to the Very Fabric, and stroked its skin with her sharpened nail, a claw as diamond, and I saw the Forefathers press their faces against the skin, craving more of her touch. ‘Yssgaroth,’ she hissed, her tongue sliding through her razor teeth behind her mask, ‘the Taint which boils within you. Trapped behind the Very Fabric.’

It's simply the next universe.

The Cold was in the dead centre of the sphere, in defiance of the local gravity, a pure-black globe inside a pure-black globe. He didn’t even try to estimate how big it was, how many hundreds of metres in diameter, how much mass it must have. He found his eyes sinking into its body, hypnotised by the things that pulsed and wriggled across its surface. As he watched, a face the size of a Drashig pushed against the sphere from the inside, its huge teeth trying to bite through the membrane. Two enormous clawed hands thrashed around under the skin, doing their best to break the surface tension. Gigantic black wings flexed in skeletal sockets.
‘You see, they remembered their own past. They remembered how Rassilon had punched holes in the universe, and let some terrible things in from the places outside. So that was what they built the weapon to do. To poke a great big hole in the space-time continuum, and let the target planet get sucked through into the universe next door, to be torn to shreds by the things that live there. Complete destruction. You understand? Complete annihilation. - Interference - Book Two

Also, while this is kind of a reach, I do think there's evidence that alternate realities can diverge from Spiral Yssgaroth. When Archie MacTavish travels through the Void and contacts their universe, the Yssgaroth are still malding over their defeat by the Time Lords, never mentioning that they've defeated them in some alternate timeline.

“The Yssgaroth were wronged by a race as old as creation. Their founder cast the Yssgaroth out into the cold, trapped in their universe, desperate for salvation. The Yssgaroth has been imprisoned since the dawn of time, seeking nothing but its freedom. In exchange for my help the Yssgaroth offered me life, to heal my wounds and grant me something far greater: to become one with its being.”

But Faction Paradox purport to have armour from a reality where the Time Lords lost, which Homunculette seems to confirm the veracity of.

‘The Time Lords fought a great war, many years ago,’ Cousin Justine explained, addressing the other representatives en masse. ‘They won. If they’d lost, by the grace of Time, then this is how they would have looked.’ She raised the mask a little. Homunculette snorted again. ‘That mask shouldn’t exist in this timeline. You see how dangerous they are? Even their headgear breaks the Laws of Time. Even their headgear.’ He started laughing, for no immediately obvious reason. Bregman wondered if he was getting hysterical. Cousin Justine merely nodded. ‘Of course. There’s great power in these totems. The Time Lords would have us destroy things that shouldn’t exist. Only the family understands their value.’ - Alien Bodies

So, it's quite possible that another reality's version of the Yssgaroth interacted with the Time Lords of another reality and defeated them.

Exo-Space

E-Space explicitly has different physical laws.

‘It’s not a definite estimation, Mistress. I’m still processing the physical and spatial/temporal laws of Ecto-Space.’
‘At the moment,’ B.E.S. said, clicking her tongue, ‘the completion of our work is impossible, Mistress. My understanding of Ecto-Space physical laws—’
‘I’ve already told you, the outer-skin is inoperable. The behaviour ofthe power source will be unpredictable due our limited understanding ofEcto-Space laws of quantum mechanics. The time travel facility isunstable.’ After unravelling the last throng of cables, the Mistress got to herfeet and dusted off her hands. ‘Then we won’t use the time travel facilities.’ - The Choice

Fyi, they had to call it 'Ecto-Space' for copyright reasons.

E-Space is referred to as a negative space-time continuum.

Adric’s home planet of Alzarius, as the old Doctor had known well, was in fact in a separate negative universe of its own, but now was no moment to quibble. - Castrovalva (novelization)

As such, its space-time coordinates are reversed compared to N-Space, which is not the case with normal parallel universes.

DOCTOR: Oh, that. Yes, that recurring image of Gallifrey. Well, it's something really quite simple. The image translator reads the absolute values of the coordinates.
ROMANA: Of course it does. Real space doesn't have negative coordinates. Doctor, that disruption we came through.
DOCTOR: Well, it's just a thought.
ROMANA: It's a very nasty thought. That would mean that we're out of real space altogether. - Full Circle

This makes the TARDIS feel unwell.

DOCTOR: Yes, I'm fine. The Tardis is feeling a bit queasy.
ROMANA: Really?
DOCTOR: Yes. So would you be if you were warping about in E-space. - State of Decay

E-Space is smaller than N-space, but it's still a fully-fledged space-time continuum with galaxies.

This time he had escaped not from some monster’s cave or tyrant’s dungeon, but from a sort of pocket-sized parallel universe, called E-space.

K9: E-space, to distinguish it from the larger N-space of our own origin.

K9: The relative smallness of E-space should render fractional increments more stable.
DOCTOR: E-space is another universe. There isn't a taxi service goes back and forth.

The Word Lord Dimension & UNIT: Dominion

I've left this for last, since it's mostly personal speculation, but I do believe my evidence is adequate.

The Word Lords' dimension, whose laws are based on linguistics rather than physics, is another reality 45 billion dimensions to the left of N-Space. Since Nobody-No-One isn't from N-Space, he's immune to the TARDIS' temporal grace function. Also, Nobody-No-One describes himself as the first being in the entire multiverse to commit omnicide, which wouldn't make sense if he was a being from outside the multiverse, and is supported by the fact that he used his CORDIS to escape his home dimension and become a bounty hunter across the multiverse.

Because the term universe is only used twice in all of Nobody-No-One's appearances (in reference to N-Space and the Hand of All), the Word Lords' dimension could also be a relative dimension, but a later line from Nobody himself suggests this isn't the case. Notably, reality and dimension are terms separately applied to both N-Space and the Word Lord's dimension, so the fact that Nobody-No-One calls N-Space a universe is evidence for Nobody-No-One's plane also being a universe.

So why does that matter?

In UNIT: Dominion, The Doctor describes the Tolians' planet as 'a planet in one of an infinite number of dimensions.' When The Doctor was forced to give the Tolians' dying world too much energy from an 'adjacent' dimension for too long, it caused 'unimaginable damage beyond [the Tolians'] dimension. And the next, and the next, throughout an infinity of dimensions.' This is because energy throughout dimensions are in a specific balance.

These dimensions have vastly different laws of physics, potentially including time, as The Doctor says '[...] And I have no way of telling how far we've travelled in time, or how time works in this dimension.' Later in the story, extra-dimensional creatures start arriving on Earth, one of which were the physically impossible Skyheads; when asked how they could survive as heads alone, The Master sees it as 'A sure sign that it's from another dimension. There's an infinity of impossibilities out there across the dimensional divide.' Skyheads can also create slipstreams in the air, allowing them to travel at several times the speed of sound and bring anything associated with them (like a human rider). When Doctor Klein says this is impossible, The Master simply retorts 'That's creatures from another dimension, bringing their own laws of science with them, luckily for us.'

He claims the laws of physics in general can be vastly different: 'the laws of science can vary wildly depending on which dimension you inhabit, and that creatures travelling between dimensions can more than likely be made up of matter that becomes volatile in our dimension [...] For all you [Wyland-Jones] know a massed attack on our flying-head friends may cause a chain reaction that could ignite the Earth's atmosphere and snuff out all life on your precious little planet!'

I should note that The Master was practicing some deception and tomfoolery in this story, but everything he says is supported by the context of UNIT: Dominion.

The Master, upon shedding his guise and preventing the dimensional walls from breaking, states that 'the whole of infinity has been rescued', and that he'll become ruler of 'every dimension throughout infinity.' The whole of infinity, in cases like these, would refer to all of creation, meaning it'd at least overlap with the multiverse.

Given that the term dimension is used instead of universe (at least from what I can find), these dimensions are likely part of the multiverse, we know that dimensions can be adjacent or far away from each other, and UNIT: Dominion and A Death In The Family weren't released that far apart, I think it's reasonable to assume that the Word Lords' reality is one of the dimensions in the multiverse.

Space-Time Vortex

Universal Vortices

Currently, we portray the Vortex as a mish-mash of of all dimensions, but it's strongly implied that each universe sort of has a separate Vortex in a sense.

Firstly, when just N-Space outside of Gallifrey's Transduction Barrier was being destroyed in Doom Coalition 4, it's stated that the Time Vortex was crumbling. If it was a mishmash, there'd still be a Time Vortex around N-Space, just not one composed of N-Space's space-time.

Secondly, even before the Time War, TARDISes had immense trouble crossing into parallel universes due to range/power source issues (The Eye of Harmony even suggests that TARDISes in the Vortex are at their closest point to the Eye of Harmony, and the link between a TARDIS' Eye and the original are at their most open), yet they have no trouble crossing into the Time Vortex.

'So what about the link with the Eye of Harmony?' 'That's still broken.' 'Can't you fix it?' 'Oddly enough,' the Doctor responded, with heavy sarcasm, 'that is what I am trying to do.' He stood back from the controls and scratched his head for a moment, looking frankly perplexed. 'However, the beam is not there to be locked on to!' 'I thought you said it could be picked up anywhere in time and space?' 'It can.' 'So?' 'So, either this is somewhere outside the normal continuum, or else the beam is being blocked. I'm detecting some peculiar faint energy readings, but with the low power the receptor sensitivity is not what I would wish, so I can't make a detailed analysis.' His brow furrowed in deep thought once more. - State of Change
The logic might hold together, but the Doctor still didn’t like it. Chronovores or not, parallel universes werenasty things and did nasty things to TARDISes. But unfortunately, their options were limited and their time wasshort. Once again, he found himself facing the most uncomfortable of decisions: no choice. - The Quantum Archangel
Many (perhaps most of these) rejoin the main anchored universe as their micro-changes fall away into quantum uncertainty. When the million sloths are dead and decomposing, what effect will the colour of one hair have had? A few (the mathematics contains several high order infinities, so the number itself may be high) do not appear to rejoin, either eternally leading outside the ‘time-space’ horizon approachable by a normal time-ship, or curving back in closed loops longer than our normal ships can reach, beyond the futures we can access. - The Brakespeare Voyage

Third, the Vortex stops right before natural, universal expansion.

Hedin was worried. The source of the Effect is out of our reach. No TARDIS can make such a journey.’ He was right, of course. The Time Vortex petered out a little before the universe stopped expanding, marking the point beyond which no TARDIS could travel. - Infinity Doctors

Lastly, as I mentioned before, the laws of physics in E-Space are different than N-Space, but this also extends to the Vortex.

“Well, if it overheats we’ll just have to eject it into the time vortex, wont we?”, end quote.’ The adventuress took off her fedora and used it to cover her face. She screamed into the headwear for a good 20 seconds before putting it back on. ‘That,’ the Mistress stressed,’ was a joke. Do you really think that I would want to abandon an overheated power source and dump it into the vortex!’ She shouted as her face puffed up and became red. ‘I mean, think of the…the damage it could do! The devastation it could cause – especially in an underdeveloped parasitic universe like this one,’ the adventuress scoffed.
‘Based on information I have received,’ B.E.S. elucidated, ‘I have calculated that it is the Year of the Flame, reign of the 14 generation of House Detola. Second moon cycle, sixth season.’ The eccentrically-dressed women’s eyes were ample as her mouth was agape. ‘So I was right, we did travel through time, but how?’ ‘Hypothesis,’ the metal mustelid continued, ‘Time/Space vortex possesses unanticipated qualities in Ecto-Space.’ -The Choice

However, it'd be dishonest of me not to mention that Romana and K9 were wrong in the second quote, and merely travelled through space.

So, whenever someone or something threatens to destroy the Vortex, it's entirely possible that they're simply threatening to destroy the universe's Time Vortex.

ByAsura · Dec 26, 2023

N-Space's Vortex

In The Time Traveller's Companion, it's stated that the entire Vortex is a chicken and egg paradox; the Time Lords were created by exposure to a window in the Vortex, but the Vortex was created when the Time Lords perceived that window. The Vortex itself is the sum of the the intersections of space-time, existing alongside normal space.

Time and space are linked. They intersect at an angle determined by some alien, non-Euclidean geometry, and the place where they meet is the space-time vortex. Like a poorly enlarged photograph, the vortex is grainy, particulate. Sometimes the particles clump together at a nexus point. - Cat's Cradle: Witch Mark

When travelling through it in the 4-D War, it's noted that the Vortex crackles with the chaos of raw time. Fenris has apparently been scattered across the whole of space-time after spending 20 years (from the perspective of the Time Lords that threw him in) in the Vortex. This is consistent with The Flood, where the 8th Doctor channelled a fragment of the Vortex and was slowly becoming space-time itself.

In The Eye of Harmony, The Doctor describes the Vortex as 'a network of corridors, connecting everywhere in the universe with every web.' He then explains that the webs are 'Time, Kalan. The fourth dimension—or at least time is how we experience the fourth dimension. [...] The Vortex connects all of space and time. In here, we're nowhere and everywhere all at once. For the Daleks, finding us here will be like finding us in an infinite haystack.' In Dark Eyes 1.2: The Fugitive The Doctor states that an infinite number of times and places pass by them every subjective nanosecond during Vortex travel.

A similar description is given in Engines of War.

The Doctor laughed. ‘This is a time machine,’ he said. ‘Out here in the Vortex we’re one step removed from what’s going on.’ ‘I don’t understand.’ ‘Think of it like a river,’ said the Doctor, ‘always flowing, always rushing by. That’s time, and the TARDIS is hovering above that river. Follow it upstream and we can dip into the future, back in the opposite direction, and although we’re swimming against the tide, we can find our way to any point in the past.’

Even in The Slow Empire's region of space, where physical laws have been altered to prevent the manipulation of higher-dimensional sets (including FTL/time travel), the Vortex still exists, but it's mostly inaccessible and quite atypical.

Enter, with the Doctor, Anji and Fitz, an Empire where the laws of physics are quite preposterous – nothing can travel faster than the speed of light and time travel is impossible.
In any event, here and now, the fact is that the manipulation of higher dimensional sets, the manipulation of Time – even something so simple as exceeding the speed of light – is impossible.’
‘We seem to be travelling through an atypical infraspatial region at the moment,’ he said cheerfully. ‘The laws of time and space as such don’t apply to the vortex in any case – but here they’re not applying in a different way. It’s a bit like flying into turbulence or a sudden headwind. We’ll get where we’re going eventfully, but subjectively it might add a bit of duration. Could be just a few minutes, could be hours.’ He seemed completely unperturbed. ‘Could be years.’ - The Slow Empire

In fact, the Vortex doesn't just encompass the infinite array of futures/potential futures that The Doctor travels through. It also includes a litany of things that never did happen, or have gone missing.

Somewhere in the perplexing reaches of the space-time vortex, the mysterious region of reality that encompasses everything that has ever happened, everything that will ever happen, and quite a few things that never did or might or had gone missing, a craft disguised as a police telephone box tumbled and spun on a wayward course. - The Well-Mannered War

The Vortex exists outside any frame of reference, and underlies/supports all space-time, with realspace being essentially a shadow by comparison. So, only massive disruptions to the Web of Time will be able to deal anything more than superficial damage to its poly-dimensional, pseudo-Euclidian fabric.

THE DOCTOR: But the loop has been playing for too long, Zimmerman. That much repeated and concentrated temporal engineering, it's eroding the barrier between reality and the Vortex, and it's going to let the Tar-Modowk in. I can't allow that to happen. I have to break it. - No More Lies

The Space/Time Vortex exists outside of any normal frame of reference. Within it, light, darkness, matter and energy all blend, divide, shift and change. It underlies the whole of Creation, touching the normal Universe only slightly. Its pathways are twisted, unstable and hard to follow. A journey through these strange dimensions might take a moment and carry a traveller a million years and a billion light years from his/her/its origin. Alternatively, a journey of months in the Vortex might end in a shift of six feet and ten days in conventional space. Without being able to calculate the pathways, there was simply no telling. - The Chase (novelization)
'The entire fabric of the Vortex will be torn apart. Without the Vortex, the space-time continuum loses its support. The galaxy will simply, drop out of reality.’ - The Crystal Bucephalus
And that included a knowledge of the bizarre dimension through which the TARDIS travelled: the Time Vortex. From what he had gathered from his months in the TARDIS, if the Doctor’s precious web of time were damaged, the feedback could cause anomalies in the Vortex; the greater the damage, the worse the anomaly. What if the survival of the fifty or so Charonites changed history?
‘The Time Vortex is virtually indestructible; it is the fundamental reality which supports all of creation. In many respects, the physical universe is nothing but a shadow of the Vortex. But the link is two-way: do something unimaginably nasty in the real world, and it might just affect the Vortex.’ Roz frowned. ‘But what could be so unimaginably nasty?’ The Doctor’s voice was sepulchral as he replied. ‘A Jonbar Hinge: an event which shatters the Web of Time, rewriting history on a major scale.’ This did not bode well. ‘Such as?’ ‘Such as the destruction of Earth.’ She shook her head. ‘But Earth’s still there. We saw it.’ And the obvious defence. ‘It’s still there in the thirtieth century!’ ‘The Vortex isn’t answerable to the laws of cause and effect, Roz. The destruction could happen tomorrow, or it could happen in thousands of years. But history has been or will be altered. Earth was or will be destroyed. Excuse the ambiguous tenses – this is a very ambiguous concept.’
The Doctor cradled his fingers. ‘On certain occasions, forces come to bear on the fabric of the Time Vortex, ripping it apart and allowing the substrate– the poly-dimensional foundation of the Vortex – to erupt. TARDISes – well, Type Forties, like mine – cannot cope with these events very well.
The Doctor produced his umbrella seemingly from thin air and started to doodle aimlessly in the sand. ‘The TARDIS broke up because she was caught between a subspace infarction and a Vortex rupture,’ he said quietly, drawing an oblong shape with a light on top. ‘That particular combination of events curdled the Time Vortex throughout the solar system, and its psuedo-Euclidian geometry would have-’ That was too much. ‘In terms that a simple cop can understand, Doctor; you lost me just before the word “infarction”.’ Then again, the way her head was behaving, words of one syllable would be of little help. He frowned, smiled sadly, and started again. ‘The forces which, er, interacted with the TARDIS screwed up the Time Vortex, to put it bluntly. As far as the TARDIS emergency emergency systems were concerned, Mars and Triton could have been next door to one another. Normal rules didn’t apply.’
The Doctor stood up and shrugged. ‘Very well.’ He looked at both Roz and Chris. ‘As you know, the TARDIS was destroyed because it stalled when a subspace infarction –Rachel and Felice’s attempt to break the blockade – hit it; the Vortex rupture – the result of the disruption of future history which would have happened if Falaxyr’s plan to destroy Jacksonville had happened without my interference –exploded beneath it.’ ‘So what were those ghost TARDISes all about?’ asked Roz. ‘Even though the TARDIS was destroyed, there was still a minute possibility that the destruction of Earth – and therefore the Vortex rupture –could be prevented. This created a minor time paradox, which in turn permitted the formation of future reflections of the TARDIS – the “ghosts”, each one representing a possible future. They were hanging – floating –around because there was a chance that the TARDIS might not have been destroyed. By detonating the power source of the GodEngine, I provided that chance; as well as preventing the destruction of Earth, I also provided the energy that they needed to come back into existence.’ He waved a hand around the ship. ‘Everything happened as it was meant to.’ - GodEngine

The Dark Path describes it as 'the dimension outside time', and The Master states that he'll effectively become omnipresent when he combines the Darkheart (a structure capable of impressing energy anywhere in space-time through the Vortex) with his TARDIS.

‘Oh, I don’t have to. I’ve met them. The dimension outside time is a vast and incomprehensible place, but not uninhabited. There are beings there: creatures of intellect, whose very life-energies are unwittingly inimical to our mode of existence.’
Koschei smiled faintly, and shook his head. ‘On the contrary, my dear Doctor, it will be a very precise use of time. Once my TARDIS’s basic structure is imposed on the Darkheart, the Darkheart will, in essence, become my TARDIS. I will be able to configure and manipulate the vortex itself with surgical precision. In many ways, my TARDIS and I will be part of the vortex, simultaneously existing in every point in space and time. Omniscient, and omnipotent. Now imagine it: epidemics, war, random violence, negligence, these are things without purpose. Imagine if there were no more of such things–only peace and harmony: everyone fitting neatly into his or her place in the universe. Then, no more failures. No more deaths without purpose. No more –’

In Harvest of Time, it's stated that things in the Vortex are neither part of time nor entirely detached.

There was, of course, no sense in which the events of the Doctor and those of Captain Mike Yates could be said to be cotemporaneous, not now that the Doctor was hurtling through the Vortex, neither part of time nor entirely detached from it.

And when copying The Doctor's parlance in Just War, Bernice Summerfield describes it as a transdimensional spiral that exists in a fifth dimension outside of Minikowski space.

‘I’m not sure about the technicalities. In layman’s terms the TARDIS removes itself from Minkowski space, then integrates itself into a fifth dimension. It travels through something called the Vortex, a transdimensional spiral built by the Doctor’s people which encompasses all points in space and time. Then, the TARDIS just reorientates itself at the other end, and re establishes a plasmic real-world interface.’
Straight away Omega put his plan into operation. Entering the time vortex allowed the station to move in space without being on the spatial plane. The pilots navigated the space station towards the space-time event of the black hole and then across the maelstrom to the far side. Only then, when they were several million miles from the event horizon, did Omega order their rematerialisation. - The Evil and the Deep Black Sky

Also, I thought it was worth mentioning that the Vortex is filled with Chronons, which (according to the 7th Doctor in Time and the Rani and Interstitial) are 'discrete particles of time' that 'reflect time'. We don't know how many chronons are in the Vortex, but it's probably infinite because the Time Lords planned to tap the infinite mass of dark chronons (which are to chronons as dark matter is to baryonic matter) in the Vortex as an alternative fuel source for TARDISes in Deeptime Frontier.

Another depiction that merits a mention is Capture the Chronovore! The characters in the story are on a Vortex ship called the Kairos and have weapons designed to hunt baby Chronovores (specifically, time sensitives that inhabit the Vortex). However, time is so unstable in the Vortex that they have to stabilise it to properly target the Chronovores.

MIROY: Within the Vortex, time is a volatile, unpredictable force. This segment's eon generators stabilise a portion of the Vortex so that it exists in time sync with the [Kairos]. Think of it as a vast net cast into a stormy ocean.

MIROY: I intend to accustom [the Chronovores] to the natural flow of time before we leave the Vortex

BLIXEN: 'And so we force those monstrous creatures out of that unstable mishmash of Vortex time, and into a fixed zone where we can shoot them

Princess Natalia (who, tbf, is a complete novice) claims that capturing Chronovores is a matter of 'accuracy, and a healthy appreciation of multi-dimensional mathematics', and her people consider the Vortex to be the 'wildest part of space.'

So how can something composed of all space-time and intersecting every point also exist outside of space-time—everywhere and nowhere—and its frame of reference? Well, in The Time Monster and The Quantum Archangel, it's explained that the structure of space-time is granular, meaning objects can be pushed into the interstitial gaps in time/reality and technically exist outside space-time.

RUTH: Ah, Stuart. Where's the professor?
HYDE: Search me. He was here a couple of minutes ago.
COOK: Who is this fellow Thascales, anyway? I've never heard of him.
PERCIVAL: Oh, an excellent background. Surely you've read his paper on the granule structure of time?
COOK: All I can do to keep up with the departmental minutes. I leave all the rest to Proctor.
BRIGADIER: That's a fearsome looking load of electronic nonsense you've got together, Doctor Ingram? How does it all work? In words of one syllable.
RUTH: I'll do my best. Well, gentleman, to begin with, time isn't smooth. It's made up of little bits.
HYDE: A series of minute present moments.
RUTH: That's it. Temporal atoms, so to speak. So, if one could push something through the interstices between them, it would be outside our space-time continuum altogether.
BRIGADIER: Where would it be then?
RUTH: Well, nowhere at all in ordinary terms.
BRIGADIER: You've lost me, Doctor Ingram.
COOK: And me. I've never heard such a farrago of unscientific rubbish in all my life. It's a impossible situation.
HYDE: But we've done it. We shoved that vase through and brought it back, in there.
BRIGADIER: But shoved it through where, for goodness sake?
BENTON: Sort of through the crack between now and now, sir.
HYDE: Right, you've got it.
BRIGADIER: Well I give up. It's beyond me.

It was true that TOMTIT was capable of moving solid objects through the interstices of reality, taking advantage of the granularity of space-time. But that was nothing more than a side effect, the unique selling point that ‘Professor Thascales’ had used to drain hundreds of thousands of pounds from the Newton Institute budget. In truth, the project was much, much more: its true purpose was to breach the Crystal of Kronos, a multidimensional prison containing a godlike being – Kronos, greatest and most fearsome of the Chronovores.

The Vortex is also stated to exist outside of space-time in the same episode.

DOCTOR: Ah ha. Yes. Yes, so far, so good.
JO: How long's it going to take us to get there?
DOCTOR: Well, that's the curious thing. No time at all. We're outside time. Of course, it always seems to take a long time but that depends upon the mood, I suppose.

And when The Doctor knocks a factory ship into the Vortex in War of the Daleks, he outright states that it's simply travelling through interstitial space. For context, he believes the factory ship is the same one that landed on Vulcan in the 21st century, despite War of the Daleks explicitly taking place some time after the year 4000.

‘And there it goes,’ the Doctor said, with a smug expression. ‘The factory ship is entering the vortex now. The Thal ship is clean.’ He cut the power, and the rotor fell silent. ‘Let’s reel these in, shall we?’ He started to pull on the wiring. ‘That’s it?’ Sam asked. ‘Flick a few switches, and the Daleks are defeated? The factory ship’s destroyed?’ ‘Yes and no,’ he answered, jerking on the wires, as Sam and Chayn helped. ‘Yes, the Daleks are defeated. For the time being. And no, the factory ship’s not destroyed exactly. I rather think it’s just been flung back through interstitial time and space.’ Chayn stared at him in horror. ‘Then we’ve just sent it somewhere else! We’ve not solved the problem at all!’ ‘Chayn, in another time, and another place... I think I already have,’ said the Doctor. ‘Believe me. Please.’

Neverland even describes the Vortex (where the Dalek fleet in The Time of the Daleks were trapped) as interstitial space.

MATRIX 3: Rassilon Era, Gallifrey, 5892.5. Files on Doomsday weapon stolen by, by, by. Rassilon Era, Outer Planets, 6241.1. Chancellor Goth visits Terserus. Rassilon Era, Etra Prime, 6776.7. President Romana vanishes on routine mission . Rassilon Era, Gallifrey, 6793.8. D-D-Dalek invasion force repelled by President Romana. R-R-Rassilon Era, Interstitial Space, 679. (struggling) 6798.2. Dalek Time fleet captured in vortex and, and, and. Dalek Time Fleet captured in can't remember! I can't remember! I can't remember!

To expand on what Interstitial time is, Falls The Shadow explains that it's an envelope of non-space and non-time, underlying the real universe and surrounding every space-time event. This is because the 'gap between now and now' is technically a zone of nullity. Events in Interstitial Space just are.

‘He’s dead. He drove his car into a wall in the mid-seventies. His body was burned beyond recognition. Nasty.’ Winterdawn squeezed the arms of his wheelchair, his knuckles whitening. It was a habit. ‘Until then he’d been working at Cambridge on his own theories into “interstitial time”, by which he meant...’ ‘An envelope of non-space, non-time,’ the Doctor interrupted, ‘underlying the “real” universe. It surrounds and separates every space-time event. A theoretical zone of nullity; “the gap between now and now”. Literally, outside reality.’ He smiled smugly.
The experience had lasted for no time and forever – it couldn’t be compared to such limited concepts. It just was.

Similarly, things don't really exist in the Vortex because it's made up of no-time and no-space. This also explains why creatures don't simply die when exposed to the Vortex—they're transposed through infinity and non-linearity, between the interstices of time, like Fenris.

And that was where the trouble had started. Cwej’s people talk about something called the “vortex”, which nobody really understands properly, but which is supposed to be a kind of no-space and no-time that connects all the other points in the universe together. The way Cwej explained it, the only way you can get into the vortex is by falling through the cracks between one second and the next, and I think that was how the time travellers travelled. By forcing open a crack, squeezing their way into the vortex, then popping out through a different crack in a different time-zone.
When Cwej’s employers left their remains behind for the Gods and the archaeologists to pick through, they scattered their leftovers through time as well as space, losing some of their old bones in the gaps between the seconds. According to Cwej, though, people who had accidents in the vortex didn’t die. They couldn’t die. They were torn to pieces, bent out of shape by the currents that ran between the time-zones, but they never got the chance to be buried.
‘We’ve been in the vortex. We’ve been trapped there since ... no. Linear time doesn’t work there. You might as well call it forever. Do you have any idea what there is in the vortex?’ ‘Nothing?’ I guessed. ‘Less than nothing. The understanding of nothing.’ I could tell he was having trouble explaining himself, even in this body. ‘When we were alive, we believed in things. Even the ones who didn’t have Gods of their own. We believed in our societies. We believed in principles. Then we saw the way things looked from inside the vortex. We saw everything in its proper context. And there is no proper context. Does this make sense in your language?’
Everything is meaningless. No, it’s worse than that. Even calling it“meaningless” puts it inside the context of meaning, and... there isn’t one.Wait. Let me explain.You draw in information about the universe around you, through youreyes, through your ears, or through whatever other senses you were bornwith. Your nervous system starts building webs to catch the raw data,filtering the information, shaping it into something that looks as if it makessense. All your principles, all your beliefs, all your laws… just filters, waysof dealing with what you see and hear and sense, of forgetting how smalland amoral your life really is. And when people with the same filters gettogether, that’s what you call your “culture”. Civilisation is a filter. A romance. A lie, if you like. And we always knewit was a lie, even before we ended up in the vortex. I think everybody knows it, on some level, but the fact that we were civilised meant that wecould cushion the shock and get on with our lives. It’s different, once you’ve been in the vortex. Once you’ve seen how small the romances are. Once you’ve had your nervous system ripped out,and lost all your filters. All those ideas about philosophy, and society, and ethics...
‘But you said it yourself,’ I told him, trying not to choke. ‘You’re immortal. You’ve spent forever in the vortex anyway. I mean, thirty years -’‘Is nothing to us,’ the Horror agreed. ‘No time to wait.’ - Dead Romance

When The Doctor enters the interstitial gap, he sees eternity expanding into 'every conceivable direction.' It has topography and colours that are too complex for the real universe.

It took me five years. I have found a way to physically enter the interstitial gap.’
‘I’m going into the interstitial gap tonight,’ Winterdawn continued, ignoring the concerned expression flashing across his daughter’s face. ‘I was going to take Truman, but I’d prefer it if he stayed behind with the tetrahedron. And I don’t want to go alone.’
Interstitial space unfolded. It was an incomprehensible sight. For a second Winterdawn’s mind rejected everything around him and he was plunged into a shroud of darkness. Then the shroud slipped. Winterdawn was reminded of a kaleidoscope – a banal analogy, but the best he could manage. The colours were clear and precise and sharp. They sang. Floating and merging and swirling into a whirlpool. Even the colourlessness was beautiful. Winterdawn had never realized that grey could contain so many tones and shades and mixtures.
‘I see,’ the Doctor replied. ‘Perhaps... ? Yes.’ He stretched an arm into the psychedelia. His fingertips seemed to penetrate the skin of the interstix, sinking into invisibility. His knuckles, hand, wrist and arm were consumed by the envelope of interstitiality.
They took Cranleigh’s revised mind and shaped it, built it a body from the stuff of chaos from interstitial space, the building blocks of reality. This proved a partial success. Their creature seemed perfect but his body structure was unstable; there were physical defects. But it lived.
The Doctor had never realized how claustrophobic an infinity could feel. He travelled through the vast wildernesses of time and space dimly aware that there were limits to his world, too distant to lace his wanderlust with boredom. He would never see everything. Here interstitial reality expanded into eternity in all conceivable directions. He and Winterdawn were nothing, less than beads of water in the ocean of reality. They were without depth or weight. But somehow infinity seemed to crush around them, tightening like the darkness in a prison. It was a cell of inconceivable magnitude perhaps – but still a cell.
The interstix flickered around him – meaningless patterns dancing on an infinitely distant, infinitely large cyclorama. He could see it perfectly. Something like a sigh passed his lips.
The interstitial light strobed violently, settling down as a swirling mist, tinged pink by leaping and writhing will-o’-the-wisp lights on the fringes of the interstix. The Doctor ignored it. He was becoming too accustomed to these changes of scenery.
They watched together as the interstitial world turned inside out, displaying patterns and colours and designs too complex to be conceived in the real universe. The Doctor smiled. At times he thought he could see people dancing in between those shapes, people and creatures from a thousand worlds and a million times. His eyes followed the tortuous geography, trying to find an end to it, certain that there was none.

Probably the best example of interstitial time and its connection to the Vortex is, fittingly enough Interstitial. A Proximan research team use the time-reflective properties of chronons to capture a droplet of interstitial time (aka, the 'Chronon Seed'), reaching 'between now and now.' The Doctor describes interstitial time as 'a powerful theoretical space of time that exists between the beats of planc time', and clarifies that 'interstitial time is so infinitesimally small that no one can really measure it, only theorise.' The researchers succeed, but they're 'projected into the very heart of the Time Vortex', where they saw 'the past, the present and the future crashing and separating', and Kalu (the head researcher) became a melding of human and the energies of the Time Vortex, allowing her to access interstitial time and manipulate time in realspace; while inside a 'small fraction of interstitial time that touches every other aspect of interstitial time, past, present and future', Christopher Jennings (Kalu's subordinate) describes himself and Tegan as 'nowhere, everywhere' and 'nowhen, everywhen.' Jennings isn't aware of whether he and Kalu were in the pocket of time for millennia or a few moments.

For reference, Kalu and Jennings only survived because they were exposed to the energies of a weapon capable of erasing beings from time and space. If anyone else touched the Chronon Seed, they'd be 'dispersed into the Time Vortex.' In fact, the process removed Kalu from normal universe that 'flexing her muscles' (aka using her time manipulation powers) inside realspace causes her to be 'plugged into the Web of Time' like a normal person, suggesting that she's not even part of the Web of Time normally.

So, I think we can comfortably conclude that interstitial time is an aspect of the Time Vortex.

Originally, when I created my 5-D Vortex thread, I used descriptions of Hyperspace from as many sources as I could find, but then I realised just how non-sensical that is. Hyperspace varies wildly from author to author. So, I'm just using sources from Craig Hinton (creator of The Crystal Bucephalus), the original dimension in Stones of Blood and some consistent sources.

In The Crystal Bucephalus, it's stated to be a subset of the universal Space-Time Vortex.

'The androids are all part of a hyperspatial token ring network. All communications between them and the webwork pass through hyperspace. Which is a subset of the Time Vortex -' 'And the rods propel us through the Time Vortex!' Tegan grinned, pleased that she had picked up something from Monroe's earlier slips of the tongue.

Stones of Blood describes it as an extension to special relativity.

DOCTOR: Hyperspace.
EMILIA: Hyperspace?
K9: Hyperspace is an extension to the special theory of relativity propounded by Einstein. Einstein's theory states-

Even if you could travel faster than light in realspace, you'd arrive at a destination before you even left your starting point, so people travel through Hyperspace (another dimension) to avoid it.

EMILIA: I still don't understand about hyperspace. [...]
DOCTOR: Oh, shut up, K9. It's all to do with interspatial geometry. [...] Here. Look, how can I explain? Listen, Einstein's Special Theory of Relativity said
EMILIA: Said that you cannot travel in space faster than the speed of light, because the speed of light is a limiting factor. If you travelled more than a hundred and eighty thousand miles per second, you'd encounter the time distortion effect.
DOCTOR: Yes. Yes, well, he was nearly right.
EMILIA: In fact, you'd arrive at your destination before you'd left your starting point.
DOCTOR: Yes. Absurd, isn't it? [...] No, that's all right. I mean, apart from space warping, which he couldn't possibly understand, there is a theoretical way of avoiding the time distort. [...] Yes, you operate in a different dimension, you see, in another kind of space.
EMILIA: Otherwise, hyperspace.
DOCTOR: Yes.
EMILIA: But I still don't know where Romana and Vivien are.
DOCTOR: Listen. They're still in the circle, or whatever occupies that space in the other dimension.

It's described as not being ordinary four dimensional space.

ROMANA: Even granting the hyperspace hypothesis, Doctor, what about deceleration? How do you decelerate an infinite mass? Anyway, where is this ship? Why can't it be seen from Earth?
DOCTOR: There's your answer.
ROMANA: That's only few feet from the circle. Why can't it be seen?
DOCTOR: Because it exists in a different kind of space from the circle.
ROMANA: In hyperspace, not in ordinary four dimensional space.

According to Whotopia, Hyperspace exists alongside the 4th dimension.

Short Trips: The Solar System - Uranus, by Craig Hinton, describes Hyperspace as a grey, non-Euclidian void of warped physics.

And then Io was gone. Jupiter was gone. Space was gone, to be replaced by a grey void. Mel shuddered as her body — along with the rest of the shuttle and its passengers — translated out of Euclidean space into the warped physics of hyperspace.

In Twilight of the Gods, it's stated that Hyperspace travel creates spatial disturbances in the Vortex, making navigation difficult.

'Now Doctor,' Jamie said uncomfortably, 'you know you can't steer the TARDIS that well.' 'Yes, Jamie,' the Doctor said impatiently, 'the TARDIS is occasionally somewhat erratic. But in this instance the Animus's use of isocryte must be creating a significant distortion of hyperspace. In fact it may have been some disturbance of the isocryte layer here that caused our original rough landing. If I disconnect the time-travel circuits I can use that to provide precision spatial guidance.'
'This is all very fascinating, Doctor,' said Lord Shallvar,'but we have a mission to undertake and very little time to spare. Can you please lift us off from wherever this is and try to locate the Animus again.' 'I'm afraid I can't,' said the Doctor apologetically. 'The level of hyperspace distortion is swamping all other sources. I'm not even certain if I can find the homing beacon now.'

The Doctor later states that the mere aperture of a portal that connects to a hyperspace tunnel has more than 3 dimensions.

'Oh, that's easily explained. It's actually the aperture to a hyperspacial tunnel, but you're only seeing its three dimensional aspect. The point of gravitational negation at the centre of Vortis would be an ideal place to locate it. The plasma creature has probably gone through it back to the star cluster core, I should think. That's where such beings normally live.'

Gallifreyans gave up teaching interspatial geometry/Hyperspace millennia ago because it was a dead end and theoretical absurdity.

EMILIA: Oh, I never studied that.
DOCTOR: Well, I'm not surprised. They gave up teaching it two thousand years ago, even on Gallifrey.

DOCTOR: Well, of course it'll work and even if it doesn't work, what does it matter? You know what they say about hyperspace.
EMILIA: No.
DOCTOR: They say it's a theoretical absurdity, and that's something I've always wanted to be lost in. Ready? Now switch on.

ROMANA: Very funny. Where have you been? What's happening? Where am I?
DOCTOR: Well, in strict order of asking, busy, nothing, hyperspace. Your friend doesn't look too well. What happened to you?
ROMANA: Well, I don't know, exactly. All I remember is Vivien Fay coming up behind me then waking up here. What do you mean, hyperspace? It can't be.
DOCTOR: Why not?
ROMANA: Well, hyperspace is a theoretical absurdity. Everybody knows that.
DOCTOR: Yes, except, apparently, the people who built this ship four thousand years ago. It's a hyperspace vessel.
ROMANA: That's ridiculous.

However, this explanation was retconned by Jorus and the Voganauts (probably because there are so many episodes and stories in Doctor Who that feature Hyperspace). The new explanation is that Gallifrey gave up on Hyperspace because it didn't allow Vortex access.

This allowed Rassilon to add in extra components that he told Euxine were necessary. He could not send a distress signal with the machinery he had; it was not meant for communication. It would have been like trying to light a fire with an ice cube. Indeed, he could not use it to do anything extraordinary, and certainly not to travel in time. However, the technology was advanced and did allow him to set up warp fields and interfere with the hyperspace dimensions. When Euxine had demanded progress and wanted to see a demonstration, Rassilon had showed the Ra’ra’vis scientist his hypothesis about using hyperspace as a means of entering the time vortex. He knew it was a dead end because it had already been tried on Gallifrey. Crucially, Euxine did not know this. The ‘experiment’ had gone ahead and, while it seemed to have failed, Rassilon had succeeded. He had pulled a ship in warp drive to him.

In fact, an explicitly non-Vortex capable Dalek ship in The Innocent (which takes place near the end of the Time War) can briefly jump into the Vortex by using its Hyperdrive.

Even setting aside Hyperspace, the Vortex is far more massive (both physically and dimensionally) than N-Space.

Firstly, in The Shadows of Weng-Chiang, the universe is described as a 'larger than average singularity.' Since the Vortex is infinite on its own plane, I'd assume that'd make it infinitely larger than N-Space.

The space-time vortex was a whirlpool of paradox; a dimension where reality was only a matter of timing, and the universe was but a larger than average singularity. As if to reflect this knowledge, at least one of the craft that travelled there was equally paradoxical, being a sprawling technological pocket dimension tucked away inside a battered wooden and concrete shell.

Secondly, Chronovores normally live in Time Vortex due to being banished, and only feed on the Lux Aeterna in the Six-Fold Realm. Millions of Chronovores in their true, ethereal forms were able to attack The Master in N-Space's Time Vortex. The Dark Path even compares them to termites in the Vortex.

Finally, an intelligent question! The Doctor turned round in his chair. ‘The time vortex is the second temporal dimension – it’s the region through which TARDISes travel, the region that TOMTIT creates a gap through to enable matter transmission. When the dimensions froze out of the void it became inexorably linked to Calabi-Yau Space. The Chronovores may live in the time vortex... but they eat and feed in what you call Calabi-Yau Space. You’re trespassing on their feeding grounds!’
The roiling blue and gold of the time vortex was obscured by the beating of a million actinic wings: the Divine Host of the Chronovores, swooping up from the Six-Fold Realm through the channel he had created for them.
His sustained assault on the host had torn enough holes in its ranks to allow dematerialisation: even with the Chronovores’ mastery over time, a point-blank artron pulse was more than sufficient to tear their ethereal forms to fading tatters, whilst a spread of Klypstromic warheads irradiated the vortex itself, poisoning them and leaving them weak and broken.
But the remainder saw the folly of remaining: with the last vestiges of their dignity wrapped round them like their wings, they took to the time vortex as a single body, a razor-tipped cloud of ivory-and-gold hatred vanishing into another realm.

‘Oh, I don’t have to. I’ve met them. The dimension outside time is a vast and incomprehensible place, but not uninhabited. There are beings there: creatures of intellect, whose very life-energies are unwittingly inimical to our mode of existence.’ ‘You mean they’re lethal.’ ‘Not necessarily. Their presence and force of will can alter the flow of time – they consume time itself. As termites consume the wood they live in, so the Chronovores exist in the vortex, and feed upon time itself.’

Yet when Artemis enters N-Space, she stresses that the thoughts of Chronovores can't be contained by the limited dimensions of N-Space (if not the black void outside of N-Space [see Black Void - No Future]).

It remembered feeding. Now it knew only hunger. That and the pain, invading it like a parasite, controlling, consuming, relentless and inviolable. –kill– the pain told it. It struggled to understand but this space, this... single universe with its shortage of physical dimensions was not enough to contain its thoughts, let alone its body. –kill!– A hatchway opened in reality, offering it a tiny glimpse of its own universe. A reward. A promise. –!kill!– It framed questions. What did the pain want? Why would the pain not let it feed? What is ‘kill’? –!do not question. Obey!– What is ‘obey’? –!!kill!!– What is ‘question’? –!!KILL!!– Alone, it was paralysed. Starving, it could only die; with the experience, finally, came the understanding that it must obey. It began to scream.

For some context, this quote is from the novel Blood Heat, where some unknown power creates alternate timeline ruled by the Silurians, specifically Morka. In No Future, it's revealed that The Monk used a spell to brainwash the Chronovore Artemis and confine her to a semi-physical form.

The Silurian Earth had been made, created. Something had given Morka the power to kill his third incarnation. Something had resurrected the Garvond. Something was showing him all sorts of alternatives. But why?
The Chronovore paused. ‘That much is true. Very well, there seems no other explanation. I’ll do that now.’ She concentrated for a moment. ‘There, I saved you from the blast. There’s symmetry to that, since it was my power that allowed the reptile Morka to kill you.’

Also, Chronovores only appear to have a physical form in realspace but exist outside time, with no No Future using the same terminology given to the dimensionally transcendental nature of TARDISes. Additionally, it's explicitly stated that they're higher dimensional beings.

DALIOS: We tried and merely split the smaller crystal from it. It cannot be destroyed.
DOCTOR: Yes, of course. It's just like the Tardis. It has its being outside time and its appearance is here.

The Doctor glanced up at the multi-dimensional creature unfolding above them. ‘I don’t know if I can get us out of this, Ace, any of us. I don’t know if Ican win this time.’
And above them still floated the terrifying form of a four-dimensional mouth, polished teeth slowly opening and closing. Benny stared up at it,and then blinked. It had vanished.

Array. ‘And why not? I thought you were a genius? In their natural form the Chronovores exist as six dimensional polymorphic lattices of photinos and chronons, bound by superstrings.’
The reaction was immediate. A few Chronovores effectively evaporated under the onslaught, their polydimensional matrices shattering under the impact; many more were caught in the edges of the blast and left injured or dying, their once perfect bodies deformed and broken.

Lastly, there's Vortex Butterflies and the TARDIS' ability to cover possible futures.

A future version of Gabby became rogue Vortex artifact that threatened the stability of the ocean of time, akin to the wake of a TARDIS, and existed as 5-D echoes of Vortex energy. She created a physically/mathematically impossible region of space-time by connecting pieces of space-time because she literally had more time than the lifespan of the universe. This is because Gabby was able to experience the whole ocean of time.

And we see that the TARDIS can travel to these possible futures, like Orphan 55 and all the possible futures where Earth survived, was abandoned instead, etc. So, logically, the Time Vortex encompasses the entirety of the ocean of time and space.

Hell, if that's not enough evidence, it's literally stated the environment of the Vortex is like that in Daybreak.

According to an extremely contradictory account from The Well-Mannered War, Time Spiral is the perimeter of the Vortex defined by Gallifrey's noosphere. For reference, what lied beyond it in this case was the literal end of the universe in the far future.

'I hope not.' Romana swallowed involuntarily. The Time Spiral existed at the parameters of the vortex, acting as a boundary to all space-time craft. Its force was powerful enough to crush a TARDIS like a piece of matchwood. 'As long as the boundary alarm's still functional.'
The Doctor patted the base of the console. 'Don't listen to the nasty lady, old thing.' He raised his voice. 'Romana, the odds against us going up the Time Spiral are - well, if I had time to waste on calculating the odds against very unlikely things happening I could tell you what the odds are.' He nodded to the junk. 'Perhaps it wasn't such a good idea asking you to help me with this. 'You've obviously got no sense of priority.'
'Better than yours,' said Romana. 'But it doesn't stretch this far. Nobody's does. Study of the later Humanian era was forbidden by the Academy. We're outside the Gallifreyan noosphere.' She referred to the statutes laid down by the Time Lords that decreed that nobody should have too much knowledge - or any knowledge at all, if possible - of conditions beyond the vortex's boundary parameters. The reasons for this decree had been lost over the thousands of years of Gallifreyan civilization, and, like most things there, went unquestioned.

In the Frontios novelisation, it's simply stated that the Vortex itself intervenes to stop TARDISes at the outer limits of Gallifrey's noosphere.

They ran back to the console room. The flashing message on the small green screen said ‘BOUNDARY ERROR: TIME PARAMETERS EXCEEDED’. The Doctor stared gravely at the warning. ‘We’ve neglected things. If we don’t put a stop to this, the Vortex will.’ Tegan ran through a quick co-ordinate check at the console. Beside her Turlough was interrogating the data hank. ‘We’ve entered the Veruna System, wherever that is.’ The Doctor did some swift mental arithmetic, which involved much finger-counting and tapping of his thumb against his teeth. Turlough turned to Tegan. ‘How can the Vortex stop us? I thought it was what the TARDIS travelled through.’ The Doctor joined then at the console. ‘We must he on the outer limits,’ he said, looking fiercely at the data base screen as though that were the cause of all the trouble. ‘The TARDIS has drifted far too far into the future.’ And then as an afterthought he added, ‘Veruna? Well, that’s irony for you. It’s the system where some of the last refugees of Mankind took shelter when the great...’ The Doctor tailed off. ‘Well, of course you’ve got all that to look forward to.’
‘Knowledge has its limits,’ said the Doctor, stretching a hand towards the Time Column switch. ‘Even for Time Lords. Ours reaches this far and no further. We’re at the edge of the Gallifreyan noosphere....’ But at exactly that moment a sudden dizzying motion caused the TARDIS to drop like a stone.

For context, outer limits refers to the Frontier itself, not the Vortex.

(A monitor on the console says - Boundary Error. Time Parameters Exceeded.)
DOCTOR: Ah, we must be on the outer limits. The Tardis has drifted too far into the future. We'll just slip into hover mode for a while.

The Infinity Doctors describes it as a map of all history (presumably defined by the end of universal expansion, as I mentioned above).

‘Time moves in circles,’ the President noted. It was an old Gallifreyan proverb, one that was literally and metaphorically true. The display showed the time spiral, the map of time. Usually, the Time Lords only concerned themselves with the first few hundred coils of the helix. The Magistrate raised his head, his teeth bared in a smile. ‘Activate the time gate.’ The President pressed the control. The image of the Magistrate snapped out of existence and the energy column at the centre of the room brightened still further. The President turned his attention to the display screen. It showed the Station making its way steadily up the time spiral. He smiled. There was something beautiful, elegant, about the Station’s progress.

The Multiverse

The first instance that proved the Time Vortex extends to alternate universes was Inferno, where The Doctor's TARDIS manages to travel between Inferno World and N-Space without falling through a gap in the Vortex. In The Time Traveller's Companion, it's also stated that space-time rifts into Vortex can be unstable rifts into parallel universes.

Time Fissures: A fissure is a direct form of spatial damage, a tear in reality caused by massive spatio-temporal flux. In many cases this tear opens a passage into the Vortex and those unlucky enough to fall into the fissure are often lost forever. Some fissures (often known as dimensional cross-rips) are significantly stronger and effectively form unstable wormholes to other places in space, time or even parallel universes. In many cases a fissure can be used as a stable, natural Time Corridor, often more reliable than a technological version, but using one in this manner will almost always widen the breach and exacerbate the damage.

In Genocide, an unstable history creates so much instability in time that the entire multiverse could fall into the Vortex and disappear.

'No, not exactly, but that doesn't matter. What does matter is the effect that your experiment in altering history is having on the structure of the multiverse. You have to realise that this little piece of Africa and another piece about a million years down the timeline are the only bits of reality left at the moment.'
'I don't know...' The Doctor pushed a few more switches on the console. 'I daren't take off. We might never land again. The whole multiverse could fall into the vortex, Sam, just dissolve as if it had never been there.'
'Time itself is losing cohesion. If complete instability occurs everything goes into the vortex: your Earth, Kitig's Earth, every star and galaxy and quasar and black hole and everything that ever was or will be or might be. The entire multiverse will collapse like a sand castle in front of the tide.'
Sabbath pointed at the child. ‘The Oracle has shown me the future. It foresaw a terrible cataclysm. An infinite number of universes and realities exist, all held in check by the Time Vortex. Beyond that vortex are creatures too terrifying to imagine.’
‘According to the Oracle, something has happened, something has changed. The places beyond the Vortex have been invaded. Now the Vortex is coming apart, fraying at the edges – nobody knows why. Whatever once sustained it has been removed from eternity.’

The Vortex apparently keeps the entire multiverse in check.

Sabbath looked down at the cowering form of the Doctor. ‘The Oracle told me how I could save Earth, become its protector. The Vortex is made up of focal points, places where the distinction between universes is narrower. In 1762 the history of Earth was changed to manufacture just such a focal point– centred on this timeline, this reality, this world.’
Sabbath pointed at the child. ‘The Oracle has shown me the future. It foresaw a terrible cataclysm. An infinite number of universes and realities exist, all held in check by the Time Vortex. Beyond that vortex are creatures too terrifying to imagine.’ I have seen them. I was one of them, long ago... ‘According to the Oracle, something has happened, something has changed. The places beyond the Vortex have been invaded. Now the Vortex is coming apart, fraying at the edges – nobody knows why. Whatever once sustained it has been removed from eternity. ’You know all about that, don’t you, Elemental? I can’t remember, the Doctor protested in his mind. I can’t remember! ‘Time and reality are eroding, splintering,’ Sabbath said. ‘When the Vortex collapses, all time and space will be shattered. Infinite universes will try tore place each other. And what waits beyond the Vortex will invade, feeding on time and space as if they were carrion.’
The Doctor sighed. ‘That Sabbath is dead – but he was merely part of the alternative reality Earth, like Hannah or Alan. That Sabbath never left Earth. Alas, another Sabbath did – the Sabbath we know – and he’s still out there.’ Fitz was still not satisfied. ‘So how did that Sabbath know all about you, what you would and wouldn’t do?’ Fitz asked. ‘The Oracle told him. It exists both within and without the Vortex. That enables it to see all realities, all possible times and spaces,’ the Doctor said. ‘That’s how it could instruct Sabbath and the Star Chamber on how to alter history, thus creating the focal point.’ - The Domino Effect

See Omniverse - Spiral Scratch below.

The Spiral is the axis of the Time Vortex, existing at its nexus.

‘Feeding time’s over,’ she then said straightening up. ‘Time to begin the chase anew!’ Monica looked up to the ceiling. ‘I’m coming for you, Doctor!’ And in a flash of light she resumed her Lamprey form and vanished straight into the heart of the Spiral that formed the axis of the space-time vortex.
Whilst there, he discovered three new atomic elements that, when combined, opened the causality loops, enabled unfettered access to the space-time vortex and unleashed the Lampreys previously imprisoned in the Spiral at the apex of the Vortex.
‘This machine,’ Rummas indicated the conical pit and the computer banks nearby, ‘is, as you rightly guess, a portal into the Vortex. Or in fact the Spiral at its nexus.’

The Spiral is composed of an infinite number of levels, which are neither linear nor multifaceted, and exists at the centre point of creation.

Imagine, if you will, a vortex. A really powerful vortex that drags into itself anything that comes into its trajectory. A vortex made up of an infinite number of well, levels for want of a better description. And if they seem to diminish as they get towards the bottom of the vortex, rest assured, it’s an illusion. For this vortex has no bottom. It is, being constructed of chronon energy, and thus temporal in nature, endless. Eternal. Bottomless, topless, middleless. It is neither linear not multifaceted in existence. It is completely unique and is, theoretically, situated at the centre of creation. Of course, in a multiverse that expands exponentially and is unfixed and infinite in nature, a ‘centre’ is a theoretical and practical impossibility For millennia, scholars have tried to fathom the true nature of what they have come to refer to as ‘The Spiral’. They have failed because, of course, they cannot tell whether each time they examine the Spiral they are seeing it exponentially or randomly.

A "pan-multiversal rip" in The Spiral spreads from multiverse to multiverse, and threatens to destroy time.

Rummas agreed with the Doctor’s assessment. ‘Yes,’ he said aggitatedly. ‘I honestly think we’re facing a pan-multiversal rip. A scratch right through the grooves of the vortex spiral, causing jumps and gashes. And if something bleeds through from one multiverse to another...’ ‘Or even one universe to another,’ the Doctor concluded. ‘That would be enough to destroy everything. Chronologically speaking.’

The Doctor's battle with a Lamprey (which can't exist in 3-dimensional space) in The Spiral affects every dimensional plane simultaneously, seemingly referring to at least 3 dimensions. For reference, the term "dimension" in this story only ever refers to spatio-temporal dimensions or the Time Vortex.

The spiral vortex was rent, torn open in multiple places, the energy from the assembled Doctors battering the two figures, distorting them along every dimensional plane, stretching, flattening, plumping, bloating, twisting and twirling them in so many directions.
The Doctor never took his eye off the creature in front of them as it rocked from side to side, drinking in the air. A Lamprey. Creatures that exist within the space-time vortex, able to co-exist in multiple locations at once but feeding off chronon energy.’ He hugged Kina tighter, addressing the Lamprey. ‘How did you get onto a three-dimensional world?’

The Lamprey are particularly dangerous because the use the Vortex to access different multiverses, including interstitial space-time. However, they feast on time haphazardly; if they were able to gain a constant across the multiverses to use as a lodestone, they could feast on all of creation at once.

Whilst there, he discovered three new atomic elements that, when combined, opened the causality loops, enabled unfettered access to the space-time vortex and unleashed the Lampreys previously imprisoned in the Spiral at the apex of the Vortex. As a result of his discoveries, the Lampreys gained unlimited access to all of time and space across the multiverses, reaching back to the creation, or forward to the destruction, of each universe, plus every interstitial point in between, wherein they wreaked havoc and unravelled reality whilst feeding on the chaos energies released as each divergent universe self-destructed.
‘We know she’s been searching for something. A lodestone to anchor herself, or themselves, at a fixed point so they can access the multiverses simultaneously rather than in the haphazard manner they do now. By having a central base, they don’t expend so much energy.’

Omniverse

Spiral Scratch

The omniverse is a collection of all multiverses (each composed of an infinite, infinitely expanding number of universes) in existence.

Of course, the theory of parallel universes, multiverses and even an omniverse was nothing new. Theories had abounded ever since work into the origins of the Lampreys had begun thousands of years ago back home. Of course, it was a chicken-and-egg situation – did the Lampreys exist because of the multiverses or did the multiverses come into existence because the Time Lords accidentally created them whilst meddling with the Lampreys’ unique existence within the spirals of the vortex.
Of course, in a multiverse that expands exponentially and is unfixed and infinite in nature, a ‘centre’ is a theoretical and practical impossibility.

It's implied the omniverse is decently large, although a definitive number is never provided in Spiral Scratch.

Rummas had crossed the room to join her. ‘It’s a sacrifice, across time and space. Across universes and multiverses. Across dimensions and –’

The Glorious Dead

The Glory is the focal point of the Omniversal Stream and the wheel upon which all of reality turns and the gateway to all creation, allowing The Doctor to see parallel versions of himself among the stream, which is comprised of multiple multiverses and encompasses / dwarfs the Time Vortex. For reference, the comics in Doctor Who Magazine were published by Marvel Comics in the late 70s to late 90s, which is why we see Marvel characters in the omniversal spectrum.

The Glory is so immense and powerful that The Master believed all his quests for power were the 'scribblings of a[n intellectually disabled] child' by comparison. He planned to collapse 'every infinite sphere of existence, every square inch of reality' into a far more basic design.

Marc Platt's Cosmology & The Music of the Spheres

Very few authors have a unified cosmology in Doctor Who, and this one seems to work very well with various other authors and the Virgin New Adventures series (a prominent chunk of the EU) and the perception of time in The Doctor who universe.

But, first, I want to get into the Omniverse. Marc Platt always uses the term Omniverse, even in situations where the term Multiverse would be entirely applicable. For example, in Paper Cuts a pre-Spiral Scratch Sixth Doctor says 'When you're a traveller on the temporal highways and byways of the Omniverse, being late is never an issue.' This isn't limited to Marc Platt, either, as Paul Cornell sometimes describes timelines as a branch of the Omniverse.

The Doctor ignored her, taking a long gulp of tea. ‘So if it wasn’t a natural branching of the omniverse it must have been created artificially.’ - No Future

So it's hard to tell whether or not Omniverse is used interchangeably with Multiverse in this case, especially since 'sideways in time' is a multiversal thing. I'll just assume it's the Omniverse, though.

With that out of the way, let's start with the Possibility Tree.

The first mention of a World Tree in any capacity is The Curse of Fenric.

DOCTOR: The Well of Hvergelmir, deep beneath the ground where broods of serpents spew their venom over the roots of the Great Ash Tree.
MILLINGTON: The Great Ash Tree. The soul of all the Earth.

The novelization, written by Ian Briggs (supposedly a colleague of Marc Platt, from what little I can find), makes it explicit that the Great Ash Tree is the Yggdrasil.

Standing against them, at the head of a mighty army of dead men, shall be the wolf Fenric, the Great Serpent and the evil Loki who was once a god. Odin, the lord of the gods, will slip away and go alone to the Great Ash Tree, where he will ask the Well of Mimir for advice. But the well shall remain silent, and Odin will return to the gods heavy-hearted, knowing that this is the end.
‘Now is the time,’ Millington turned slowly. In a flash of lightning his face was filled with evil. ‘The chains of Fenric are shattered! The gods have lost the final battle! The Dead Men’s Ship has slipped its moorings, and the Great Ash Tree itself trembles to its very roots!’

The Battlefield novelization by Marc Platt also features the 'Yggdras'.

At its heart stood the symbol of its birth. Carved from a fallen bough of Yggdras, the world tree, ringed by a single bench with room enough to seat one hundred and fifty knights. Arthur’s table, at which all men were honoured and equal. Where even the king had no throne.

Notably, alternatives and possibilities are described in this novel as webs and vectors that surge forwards, backwards and sideways in time.

The storm surged around the TARDIS as it hovered between realities. Its sensors sought out the instigator of the signal. Alternatives. Possibilities. The way was no longer clear. Which way? Which universe?
A diagram flickered up on to a monitor. Vector lines diverged like a web in all directions from a central core. Angular runes marked each line, shifting both colour and shape across the wide range of transmission frequencies from the fluting signal.
The web lengthened out into a wire-frame tunnel down which they travelled. From every section of the frame, new webs of transmission vectors branched out.‘ It’s covering everywhere at once,’ he said. ‘And I do mean every conceivable where. Surging out through the cosmos. Forwards in time, backwards in time... and sideways.’ ‘Sideways!’ ‘Yes. Across the boundaries that divide one universe from another.’

The Gallifreyan, Pekkary, described himself as a single possibility on one branch of the Tree of Infinity.

"The details are changing." He knelt and touched the glowing flowers with his brutal claw. "There are many things I do not remember. So I may not live long. I am only a possibility on one branch of the Tree of Infinity." - Cat's Cradle: Time's Crucible

Like I said above, The Doctor of an unbound universe in Auld Morality describes Imagination and Possibility Theory as relative dimensions that the Time Lords don't explore. The Doctor himself explores alternate timelines using a Possibility Generator. Said timelines are 'real' in their own right, but are still artificially generated, physics violating domains that The Doctor controls.

It's explicitly stated that each and every moment generates infinite possibilities, which branch out like a tree: 'From every moment there are infinite possibilities. They branch out, tree-like, in every direction over and over—tangling through each other. From the 'Possibility Tree', The Doctor sees multiple variations of Gallifrey, including a Gallifrey where 'the rulers are as steeped in blood as we're steeped in dust', 'where the world was cursed and the children died', 'or sorcery ruled instead of science.' He also sees the Aurora Temporalis, 'the anvils of heaven from which all time springs', as well as cities, jungles, aliens, etc.

If it's not clear enough that the Possibility Tree is time itself, Time's Roses that grow on the tree are literally scented with memory. Plus, I have more statements below.

Now, I'll discuss Time's Music and the Music of the Spheres, which was first introduced in Short Trips: Time Signature.

The Eternal, Time, is said to have poured time—in the form of dust—into the blank universe and plays a melody called Time's Music.

As the endless, timeless flute melody played, she stood pouring the glinting dust into the bottomless crevasse. Just as the Mother Goddess of the Old Time legends had poured Time itself into the void of the empty Universe.
The same tune stirring different memories. The dust of Time glittering like falling mirrors, trickling like sand in an hourglass. To stop it you might more easily stand a Pythia on her head.
The timeless music of Time. A line of cool melody from the flute, like the wind singing, so calming, so persuasive, so frightening. Both objective and deeply subjective. The fretwork on which perception is hung. Make of it what you will, the flute plays on.

As The Doctor is travelling through the Vortex, strings thrash through 13 dimensions, kicking up the quantum foam and possibilities, and creating the Music of the Spheres by dancing together.

The string twisted like a drowning snake, thrashing through 13 dimensions. It jerked and jumped in harmony with its partners, kicking up quantum foam from the substrate of reality. Together they danced and, in dancing, sang the song of the spheres, loud and clear, keeping time with the cosmos. Vworp. Then the song began to shift. The quantum froth came to a boil, changing its tune, skipping to and fro across the boundaries between there and not-there, between be and not-be. The strings resonated to a new noise, coalescing out of quantum clouds into particles that, in turn, accreted into atoms. Vworp. As they fell in step with this new song, reality swayed to its rhythm. There, not there; be, not-be; and back again. Interference, pulsing back and forth until, finally, the new song swamped the old, drowning out its frequencies. Quantum probabilities resolved, collapsing into physical structures, trumpeting this new melody out across the cosmos for anyone who had ears to hear. - Short Trips: Time Signature - Resonance

For anyone wondering, the 'Spheres' are a reference to the Celestial Spheres. The Time Lord Caleera even planned to destroy space-time itself by amplifying the resonance of the 'Spheres' at the moment of universal alignment.

LIV: So what's the plan? They're using the Sonomancer?
EIGHT: Yes, placed inside a resonance engine.
HELEN: You said. What is that?
DOCTOR: I think I can guess, carry on.
EIGHT: One push from her at a precise spatio-temporal location when all celestial bodies are in alignment and the resonance of the spheres will build, build and build exponentially, leading to the destruction of everything. - Stop the Clock

The strings are the strings of the omniverse, and the music they play is time moving through space, lighting stars and turning spheres.

The tree is Time, old as itself, gnarled and spreading wide, blotting out the clear sky with infinite possibilities. High amongst its branches clings something like anorchid. Its flame-white petals flicker and change into infinite shapes. A ragged saucer, a trumpet, a tulip cup. A song resonates forever here, whispering its music to the leaves. It is Time moving through Space, lighting stars, turning spheres. The shapes we imagine as the rose and the orchid hear the music playing on the strings of the Omniverse. The music nourishes them. They reach deep to touch it. They think of it as theirs. They are very proprietorial about it. It is a perfect harmonic sequence, no variations allowed, that must be kept perfect, that no one should hear.
The tune! That was it. You can’t have a tune without time. His thoughts stirred themselves. A wordless tune that sucks time from everything else just to exist. Or whatever sings the song. Whatever was circling the TARDIS or circling in his head. - The Hunting of the Slook

The Tenth Doctor similarly describes the Music of the Spheres as the sound of the universe, represented through the filtered gravity patterns of galaxies.

THE GRASKE: Music of the spheres, is what?
THE DOCTOR: Well - you get all those planets revolving round suns, and all those suns revolving round in a Galaxy, and all those Galaxies revolving round each other. If you take the gravity patterns, feed them through the TARDIS harmonic filter that, Mr Graske, is the sound of the Universe.

The Music of the Spheres are basically resonance across the universe.

DOCTOR: Sonomancer, what does it mean?
CALEERA: I alter the universe with the power of sound.
DOCTOR: Hello I'm the Doctor, I'm here to help you overthrow your evil overlords. You see I can do that too.
CALEERA: You are wilfully ignorant. I control the resonance within all things. The vibration of atoms, the pulse of electrons.
DOCTOR: The music of the spheres, something magnificent, and you use it for destruction. - The Sonomancer

The Music of the Spheres can even be manipulated to rend open the Vortex for universal travel.

Then he began, one finger at a time, to play a slow, slow melody at once mesmerising and menacing. ‘Of course, how the rent into the time vortex could be opened was always a source of debate, but there was an idea mooted that the key was a sequence of notes. A set of chords that has sometimes been equated to the music of the spheres.’
‘You might not get a chance. It’s the song you should be terrified of. It opens the door between the Slooks’ home and this universe. This is a scientific voyage, not a suicide mission!’

So what are the strings of the Omniverse? Frankly, I can't give a definitive answer, but the Pythia created an early version of the Web of Time called the Cat's Cradle by weaving the dimensional strings of time itself. Chapter 19 of Cat's Cradle: Time's Crucible, where much of this information is revealed, is called Superstrings.

Lost voyagers drawn forward from Ancient Gallifrey perform obsessive rituals in the ruins. The strands of time are tangled in a cat's cradle of dimensions.
The Pythia foresaw a point when there might be no more seers. The web of thought that linked the augurers and oracles of the Universe was broken. The veil of Time would no longer be pierced by thought, it would have to be physically travelled. She had foreseen that long ago. Why else had she instigated the Time program? Her powers, branded as superstition by the faithless, were drawing to an end. The Universe would become an empty and desolate place. She would soon be a lone voice. That is what the eye of the Sphinx showed her. But such visions could be clouded or misunderstood. She reached for Vael's mind again. Vael held keys that would unlock the future. In the darkness where Vael was trapped, she had touched another mind as well. It was a mind of great power, a mind beyond the strictures of Time. In that briefest encounter, she had immediately recognized an equal. She would find this mind again and consult its wisdom, just as the mighty had once come to consult her. For she must know the future. But in that mind she had also glimpsed thoughts that chilled her. It claimed to be born of Gallifrey. But she was Gallifrey, knowledge and life. How could she not know this mind already? Unless . . . unless it had yet to be born.
In the Cat's Cradle, where Time was tangled, the tyrant despot Process had summoned its own Beginning. The monster was supervising its own birth.
The glowing criss-cross of the streets below and the dimensional strings of the cat's cradle. The Ancient Gallifreyans had excelled in entrelacement. Motives interwoven under and above, back and forth, until the start of the design was lost. Patterns and threads, ornate stone ridges on the great Houses, intricate lines of coloured plants and soil in the knot gardens, polyphonic voices in the thought pool, repeated steps in the lordly dances. A net in which they were all entangled. The strings stretched across all Time like a web. He had seen it reflected everywhere from the rich patterns of the redoubtable Miss David's carpet shop in Antalya to the ration queues of Boom City after the Great Soul Rush of "831 had failed. The universe was all enmeshed. Yet out of that chaotic fantasia of form, Rassilon had translated the TARDISes and fashioned the Matrix.
"My ship is a cat's cradle of dimensions. Infinitely variable in form. What it looks like depends on who's holding the strings. The Processes, bungling incompetent worms, have turned the whole thing inside out! This City is what remains of my ship. We never left it. And we may never again."

In The Gift, The Eighth Doctor describes the Music of the Spheres as 'endless ringing motion'. The titular Gift is designed to 'amplif[y] reality [and] feed on the resonance', so under Caleera's direction, it planned to amplify the effects of the 1906 San Francisco earthquake and the destruction of Earth to the point where it disrupted and fractured Time's Music. Had it succeeded, The Gift would have destroyed all universes: 'And if I let you outside, the name of Charles Virgil McLean will be damned throughout all universes. Except The Gift will destroy all of those, too.'

Lastly, I'll go over the perception of time as a river.

Time's currents are described as a river that moves in many directions and dimensions simultaneously.

The structure of the whole street, the buildings and pavements, was seethingly alive, and the people moving through it were participants in a slow, graceful dance. But Time's currents, unlike a river, flow in many directions at once. - Cat's Cradle: Time's Crucible

In The Skin of the Sleek and The Thief Who Stole Time, it's stated that 'raw time' flowed into an infinite number of parallel universes. If parallel universes approach too close, they can damage each other.

'To start at the start, time is running raw—rich and unchecked. Nothing slows it down yet. No scenery, no players, no plot, no wishes, nor broken legs. Just a tale told by an idiot, full of sound and fury, signifying what? [...] Bubble, bubble, toil and trouble, fire burn, cauldron bubble. Time splitting the first cell of the omniverse, time dividing time and time again; infinite universes like Sleekling rose in clusters, riddling with dreams of suns and moons all of their own, hatching and running to fill the deep of space with starlight. But sometimes croached too close, huddles too hard, scared to strike out—scorching themselves time after time; time against time [...]'

The Time Lords of the past used Funderell as a plug for what's described as a nexus of parallel timelines ('an unstable confluence of adjacent continua' / 'a lethal conjunction of timelines at the heart of [Funderell]' / 'Too many times coursing through one rickety space') in order to save the universe. However, the renegade Time Lord Sartia attempts to unleash and fully control the nexus.

Upon seeing the 'morass of converging timelines' in Funderell's heart ('There's a lot of futures down there among the pasts. All waiting to happen. Their baffle babble is what your score chews into'), Sartia sees possibilities 'at every turn', 'this way, or that, or the other', 'parallel lines that never run straight', 'Endless possibility. Time running raw on an infinite number of tracks', and 'Time dancing with space. Stars flickering like ghosts, caught by the Music of the Spheres.'

With control of time, Sartia influences Romana by showing her a possibility where The Doctor is grievously injured, and even claims that she and Romana can create universes: 'That's time lying out there. Infinite time. We can tame it, manipulate it moment by moment to whatever we like. We can shape the cosmos—any cosmos—to our own design; the Sartia-verse, the [Ro]mana verse, one each. How do you fancy that?'

However, because 'the array of timelines were tangled', the raw time that Sartia tried to manipulate wasn't connecting: 'The timelines are not it. That's not the problem. The flow is all wrong, they're pulling in opposite directions. It's not connecting.'

The Six-Fold Realm

Fun fact, The Six-Fold Realm only has four appearances: first is The Quantum Archangel, the other two are relatively brief mentions, and the fourth is a non-canonical novel based on Craig Hinton's pitches, ideas and notes that was created by his colleagues as a charity publication.

The Six-Fold Realm, aka Calabi-Yau Space, is the culmination of the higher 6 dimensions (existing separately, but conjoined) that were ejected by the lower 5 dimensions during the multiverse's creation.

‘At the risk of sounding like a high-and-mighty Time Lord, I am a high-and-mighty Time Lord. And to quote one of my elementary texts in the matter: “And in the aftermath of Event Zero, eleven dimensions did fight for existence. Five were triumphant – together they did become the three dimensions of space, and the two dimensions of time through which we travel. But the remaining six dimensions did still exist: although beaten, although denied their dominance, they curled and curdled amongst themselves to become a six-fold universe, separate yet conjoined.‘“ They formed a realm all their own – a universe in which the Transcendental Beings could thrive and prosper without interference from the lesser beings. A realm protected by the Great and Ancient Covenant.'
It had watched Event One fill the multiverse with new matter, new energy, new life. It had stood by as the Old Ones from the revenant universe had continued their ages-old war: it had remained impartial as the primal evil had shattered into an infinity of shards that spread across space.

Its knots exist at every point of space-time, explaining why N-Space has 11-dimensions despite the book repeatedly stating that there's only 5 (the 5th of which is in the Vortex).

The knots of Calabi-Yau Space, existing at every point in the four familiar dimensions of space-time as well as throughout the time vortex, were inaccessible to the majority of races in the cosmos. Even the most advanced of them treated it as an abstract set of solutions to some esoteric quantum equations.
Time ram: one TARDIS materialising at the same point in space and time as another, where two TARDISes matched temporal frequencies and materialised at exactly the same point in each and every one of the eleven dimensions of space and time, every particle of one TARDIS coinciding with every particle of the other.
So what did this mean? Gallifrey itself was protected by even more complex temporal defences, its worldline twisted and warped through all eleven dimensions to hide it from Enemy attack.
The Quantum Archangel laughed. It wasn’t a pleasant sound. Especially as the Doctor could now see that the laugh extended into all eleven dimensions and generated a whole raft of exotic particles which he could taste and smell. The Lux Aeterna’s influence was increasing.

If I were to speculate, I'd guess these 'knots' are superstrings, especially considering the hand they had in the Mad Mind of Bophemeral's creation, comprise the Chronovores' timelines, and extend throughout the Vortex.

He was with her now, his body conjoining with the radiant aura which surrounded her. Eternals and Chronovores were built from matrices of exotic particles, resonating superstrings that gave them power and majesty, and Elektra gasped as those matrices intertwined. But their feelings... were there particles for that? If there weren’t, then Elektra and Prometheus would create them.
Effortlessly, they took Prometheus’ timeline and unravelled it, string by superstring, back and back.
‘And why not? I thought you were a genius? In their natural form the Chronovores exist as six dimensional polymorphic lattices of photinos and chronons, bound by superstrings.’
Paul shook his head. ‘With TITAN we can examine the fundamental nature of reality, Doctor. Surf the quantum foam, examine superstrings first-hand, map the topology of Calabi-Yau Space... Doctor, this is our chance to understand our place in the universe.’
If they got the chance he was dead... if he didn’t kill himself first, of course, he noted, guiding his protesting ship through an avenue of vibrating superstrings that crisscrossed the vortex like some insane spider’s web.
Quintillions of light years of superstring material were woven into the strange matter matrix to render Bophemeral invulnerable to the ravages of time, as well as giving it a defence against those races that, one day, might attempt understanding before they were ready for it.

The physics of the SFR are vastly different to N-Space and the Vortex.

His fingers darting across the keyboard, the Master began to run the definition series that would culminate in the final program: the key to the Lux Aeterna. As he entered the increasingly complex functions he concentrated on the end result, allowing the image of the wave envelope to actually generate the parameters of the envelope. Cause and effect reversed, thanks to the insane physics of Calabi-Yau Space.
The Master had returned to his calculations. ‘E equals MCto the fourth power...’ he muttered. ‘Cubed.’ ‘What?’ ‘E equals MC cubed.’ Anjeliqua might not have been the genius that Paul was, but she still remembered her temporal physics courses. E equals MC cubed in the time vortex. ‘Not in the hexadimensional physics of Calabi-Yau Space, you ignorant...’ He shook his head. ‘Ms Whitefriar, please accept my apologies. The strain of these calculations is taking its toll. Indeed, I have to confess that this enterprise is proving to be a little beyond me. I require assistance.’

It's hard to tell exactly if the Six-Fold Realm just exists above the universe or the multiverse. For example, the Lux Aeterna is said to underpin the entire multiverse and exist at the heart of Calabi-Yau Space, but then they constantly alternate between cosmos, multiverse and universe when referring to the Chronovore's range.

The Quantum Archangel formed from the quantum foam, her physical being solidifying from the eleven-dimensional nothingness like a brand-new star.
Meanwhile, the Doctor was attempting to calculate a counter harmonic to the waveform, its involute, designed to cancel out the tunnel the Master had set up between the real world and the dark secret at the heart of Calabi-Yau Space: the Lux Aeterna.
With his imagination and her primal strength they would lead their estranged families to a common ground, to a place where all the Transcendental Beings could live together with the races spawned by this universe. The humans, the Gallifreyans, the Daleks... they would all have their part to play. As would those Transcendental Beings that had stolen away into the hidden places, regions of the multiverse that were even more remote than the darker strata, beings that had seen the universe as a challenge to be conquered, a people to be r***d, an artefact of so high a price that they would destroy everything to possess it. The Great Intelligence, the Nestene Consciousness, the Animus... Especially the darkest and greatest of the Old Ones, Nyarlathotep: after what he had done, Elektra had a special place in Hell reserved for him.
The Doctor elaborated. ‘The Lux Aeterna is the energy lattice that underpins the entire multiverse: not just this universe, but any and every other one that could ever possibly exist. It is infinite power, but without form, without reason.
Because where those six stunted dimensions crossed the other five of the space-time continuum and the time vortex, they created a point singularity which tapped directly into the fundamental energies that underlay the universe: the seething primal force of the quantum foam. At the heart of each microscopic knot was a point no larger than a quark, but with the potential energy of a quasar. And each of these points linked together across space and time to create an eleven-dimensional lattice of unimaginable power that framed and defined the cosmos. A lattice that the Time Lords – to their cost – knew as the Lux Aeterna. The eternal light. The food source of the Chronovores.
The Chronovores, weakened by their isolation from their food source, would be no match for his newly augmented powers. And with the energies of the cosmos itself flooding through him, he would be free to commit the greatest act of genocide the universe had ever seen.

And, yes, this isn't some kind of Marvel thing where iterations of the multiverse are referred to as cosmoses. They say cosmos = universe outright.

According to the council’s ruling, the Chronovores were nothing but vampires: subsisting on the primal energies of the Six-Fold Realm, only truly living by drawing the life essence from the moments of choice, where they could thrive on the what-ifs and the what-might-have-beens, keeping this cosmos alone in the multiverse. An empty existence, a life of loneliness.

In Bloodlines and The Shadowman, the Guardians (aka, the Accord) explicitly see and preside all realities.

She turned back to the Accord. ‘And since you never act directly on the corporeal plane, I’m guessing that something threatens the realities of the quantum universe?’ ‘You are correct. Although this human was not lifted from your quantum reality, but rather from the essential timeline.’ ‘Essential?’ The Accord paused. ‘To use the vernacular of your planet, it is Timeline Zero, from which all other realities branch and intersect. Your world, Timeline One, if you like, is the strongest new reality created by the temporal splintering of the fracture point.’
Time was cracking. Falling apart. Two bloodlines were being disrupted, no longer entwined the way they ought to be. A fracture point in Earth’s history, a key moment upon which hinged a multitude of future events, was splitting apart. New, unstable realities were being created. And as a result of all these things the essential timeline, the one from which all alternatives branched and intersected, was being destroyed. This is what the Guardian of the Quantum Realm told Eileen.
She was in the quantum nexus, a temporal holding room within Calabi-Yau Space, created by the beings sometimes known as the Six-Fold-God, Time’s Guardians or, as she had known them, the Accord.
Anne hadn’t. Even now she could feel a migraine coming on, brought about by the ever-changing spectrum of colour and light that made up the quantum nexus. What she was seeing, as was previously explained to her, was the timelines of the universe. Billions of them. Such was their vastness that the human mind could only translate them as colour and light. It would take beings as existential as the Accord to make sense of them.
‘So, therefore, you need me and Eileen for something. What is it?’ ‘As you said, I cannot be seen to act in corporeal matters, but I must also protect the quantum realm. We must repair the damage to Timeline Zero; if the Traverses and Lethbridge-Stewarts do not meet at the London Event, then Timeline Zero will collapse, as will all tangential realities.’ ‘Realities like mine?’ ‘Perhaps. Your timeline is one of many created by this disruption; the quantum realm is in flux. It is hard to know which new reality will stabilise too.’
Anne smiled. ‘I don’t think the Accord sees the difference. It views all realities, all timelines. To the Accord, all beings are one, no matter their quantum origin.’

Time's Champion is even more explicit, but there's still some vagueness.

'It is as we should have feared, and I am the most to blame; when I bargained for the life of Paul Kairos, I should have known that should he later have any offspring, then not only could such a child be a threat to the fabric of reality but, in the eyes of the Higher Beings, a breach of the Ancient Covenant, and an act of war between the Chronovores and the Eternals. That war has begun and Earth is only its first victim - if we don't act fast then Gallifrey, the Web of Time, even the multiverse will collapse into the void!'
Their presence was unmistakable: the Six-Fold god for a Six-Fold Realm, the six, primal entities of the multiverse, whose will in unison defined and defied the cosmos: Structure, Entropy, Equilibrium, Justice, Life and... Wait, Paul realised, they are incomplete, where is...
Paul felt the patterns of reality curdle and twist beneath him; he turned and saw where the Chronovores were driving him: straight into the boiling plasma cauldron of the Lux Aeterna, the power source of the multiverse - he would die if he fell into that!

Voids

Black Void

In The Mind Robber, The Doctor uses the TARDIS' emergency unit to slip sideways outside of reality into a black void outside of space-time, where it breaks up.

DOCTOR: But it moves the Tardis out of the Time-Space dimension. Out of reality!
JAMIE: Well, fine. Reality's getting too hot anyway.

DOCTOR: Well, because, well, we're nowhere. It's as simple as that. I'll be in the power room, Jamie.
JAMIE: Aye, right. Hey! What does he mean, we're nowhere?
ZOE: I don't know. I suppose he means that outside the Tardis now is nothing. Just nothing.

ZOE: But if there's nothing outside the Tardis and we're nowhere, then what is there to worry about?
DOCTOR: I don't know. But you see, the emergency unit is limited to a certain time simply because it's...
ZOE: Because it's dangerous to stay where we are for any longer, yes. But we must be safe at the moment, otherwise the unit wouldn't let us stay here, would it?
DOCTOR: You're interested in what's outside the Tardis now, aren't you?
ZOE: Well, curious, yes.
DOCTOR: Zoe, listen to me. If we move outside the Tardis, we step into a dimension about which we know nothing. We should be at the mercy of the forces outside Time and Space as we know it.

The Doctor tapped the black box. 'A nifty gadget for use in extreme emergencies. If I activate it we'll just drop out of everything, quite possibly forever, taking the Hive with us. We'll be outside your influence.' 'You would not dare, Doctor,' called the Guardian. 'You would rather die.' The Doctor hunched over the console and readied his finger above the box. 'Probably, in the normal run of things. But occasionally it does one good to surprise oneself. And I'd rather disappear than grovel to you.' He turned to Romana. 'I'm sorry.' Romana swallowed and curled her fingers around his above the control. 'There's no alternative,' she said, trying to keep her voice even. 'Have you ever done this before?' He smiled. 'Once. I ended up in the fictional realm. I suppose it wasn't such a bad place.' Romana shuddered at the thought. 'Then we'd just be characters, not real people.' 'I can think of worse fates,' said the Doctor. - The Well-Mannered War

The Black Void itself supposedly exists beyond The Black Guardian's influence, despite the end of the universe being a region of space-time where the White Guardian can't interfere.

The Doctor tapped the black box. 'A nifty gadget for use in extreme emergencies. If I activate it we'll just drop out of everything, quite possibly forever, taking the Hive with us. We'll be outside your influence.' - The Well-Mannered War

When Nyssa and Adric were both outside and beyond space-time in Logopolis, they could see the whole of the universe.

ADRIC: We're hovering.
NYSSA: Outside space and time.
ADRIC: But the Tardis isn't supposed to do that.

The Black Void beyond universal expansion is merely vacuum.

Mortimus had been planning for decades, accumulating information and stealing useful devices, financing his operations by taking on discreet commissions across the universe. It had taken time for him to repair his TARDIS while stranded on that ice planet, and while he was constructing new circuits, he’d plotted. Once he had the necessary knowledge and equipment, he’d taken his TARDIS as far as it would go, out to the edge of the universe. Here there lived things that even Time Lords talked of in whispers, here stretched the great wave of quasars and dark matter in continuous explosion. Ye shall go no further. If you looked back, you’d see the complexities of the structure that contained the galaxies, a tangle of gravitic strings and muscles. If you looked forward, beyond the roar of universal expansion, beyond the background flare of first creation, there was only darkness. It was said, in the forbidden texts, that there was life even in that darkness. But then those who wrote the forbidden texts were romantics, scared awake at nights by what they had written. Mortimus was not scared by what lay in the void beyond the universe. His quiet hatred extended beyond it, made the vacuum just another distance inside the hand of his ambition. On the scanner screen of his TARDIS, two mighty collapsars spun, new-formed suns exploding as they burst across their event horizons. The solar debris was blasted away in two great relativistic jets. The blaze of white light that the system gave off was enough, even from the small area of the scanner screen, to pick out the details of the chamber that Mortimus had prepared for this occasion.

The Monk summoned the Chronovore Artemis in it.

Artemis!’ he shouted. ‘I call you! I call you in the name of Rassilon The Ravager! I call you in the name of Omega The Fallen! I call you in the name of the Other, he who completes the Trinity and whose name is forever lost! You must enter the continuum and pay me heed, for I would give you sustenance!’ She appeared straight away, to the Monk’s surprise. A simple figure, standing in the corner of the pentacle, a woman in a black dress. She had long black hair and a shining red mouth of immaculate teeth.

The Dark was the void that existed before the Big Bang, a cavity in space-time where the universe was spawned. It was shredded by the Big Bang and reduced to a 'half dimension', but continues to exist outside time.

The Doctor cleared his throat. 'I've heard the theories. Legends of powerful forces for good and evil that survived the Big Bang.' Cadwell nodded. 'The Dark is none of those. The Dark is all that remains of the void that existed before the Big Bang, the cavity in Time and Space, if you like, where those forces were first spawned. The Dark was shredded by the forces that created our universe, but it was not destroyed. For billions of years it lay spread across the universe, like the very faintest of shadows. Over the aeons it managed to reform itself, and finally coalesced amid the primal matter that became the planet Akoshemon.'

The Void even exists in the gulf between galaxies.

Apparently oblivious to Tegan's reservations, Nyssa continued, 'It really wasn't like a dream at all. There was definitely something or someone in the room with me, in the shadows. I got out of bed and followed it into the darkness... I didn't want to, but I had to. Some kind of compulsion, I suppose. It seemed so cold, and dark, like the deep space between galaxies. Empty and merciless...'

It's not simply a void, but a non-void without substance.

'There is a great void here, in this moon... an empty place, and yet not empty. It is filled with something I cannot describe, but I know it is this moon's darkest secret.' Jaal's eyes seem to glow brighter. 'And there is a door...''I hate riddles,' complained Tegan. ‘A door to what?' asked the Doctor. 'The void. The non-void' Vega Jaal hesitated. "The...hunger. The craving.'
She knew with certainty that she was no longer in the TARDIS. She was floating in a void, weightless and sightless. There was nothing to touch; no wind on her face or sounds to hear. There was no way to judge distance, or time. It was total sensory deprivation. Only then did she feel the first ripple of panic, as the exact nature of her circumstances dropped like a cold pebble of fear into the centre of her mind. She expected to wake up, then. But she didn't.
Nyssa had given herself over to the darkness. She had no choice; the darkness was all there was, an unending, depthless void. She spun slowly through the unmoving blackness, or perhaps she was unmoving, and the blackness spun slowly around her. It was impossible to determine which. She had given up trying to analyse the experience scientifically: there was nothing to measure anything against. The only danger with abandoning her scientific rationale was the increased chance of it giving way to panic; already she could feel the first spark of what she knew would become a burning terror if she allowed it to kindle.

The Dark exists on multiple planes and beyond the universe's physical laws, but it has to adhere to physical laws to have a presence when it manifests in space-time.

At first they could not find it, because it had no lair: its tumescent evil existed outside the natural physical laws of the universe, like an abscess on reality. But its effects were all too apparent: greed, hunger, strife, violence, betrayal... everything that is awful and evil to us. Eventually they tracked it down, and found it in the shadows. The being they sought concealed itself there, living at one with the darkness. They called it simply the Dark.' 'The Dark knew our universe only through the complete absence of light. In time my ancestors cornered the beast and burned it. The flames were entirely beyond its ability to withstand.'
The Doctor chewed his lip thoughtfully. 'But in trying to exist in our universe, it has to find some common ground. It must adhere to some of our physical laws, or it couldn't react to anything.' 'My understanding is that it exists on many different planes at the same time,' Cadwell said. 'Yes,' the Doctor agreed. 'It's telepathic, so it has amental presence. And I know for a fact that its mental presence can reach beyond the normal boundaries of space and time. But it also has a physical existence, because we've seen the ashes and the blood that went into making it. A physical presence.'
Tegan found herself discarding the spent torch and grasping hold of the Doctor; not for comfort, just for something or someone to anchor her space in thevoid.'Is it here?' she heard Nyssa whisper. 'Very nearly,' replied the Doctor. 'It needs total darkness to achieve a physical presence.' 'Then we've lost.' 'Was there ever any doubt that we would?' asked Tegan. 'Never give up hope.' ordered the Doctor. 'Remember, the Dark craves a physical existence in our universe. Once it's fully manifested it can't go back to its own dimension.'

Upon fully manifesting, the void began to feel the passage of time.

'Time,' growled the shadow as if savouring the word. 'Yes... I can feel it now, the very progress of the universe around me.' The Doctor was intrigued. 'You mean you couldn't feel it before?' The eyes glittered like coal in the shadowy face as they regarded. the Doctor. 'Yes, what would you know of the endless, empty void that bore me? At last I can sense the soft, stealthy passage of time itself.' 'Well, perhaps congratulations are in order.' they say there's a first time for everything. Even feeling the passing of time, I suppose.' The Dark hissed. 'You don't understand, Doctor. How could you? I have drifted, formless and outside of time, for uncountable millennia. I have been forced to watch from the sidelines of a half dimension, unable to interfere. But not any more!'

The Void is separated from the universe by the Interface, from which it can attain pseudo-physical form and attempt to optimise the universe.

'And is this what it looks like?’ said Lucy, incredulous. ‘Snatching people out of the world and dropping them off in a different life? Changing things willy-nilly to suit yourselves?’ ‘We improve things,’ implored the creature. ‘We optimise.’ ‘And what about me? What about the people who knew Hobo? Do we just forget, is that it? What about all the things he did, the things we did? You have no idea the lives that man has saved, how many times he saved me!’ The creature shook its head slowly. ‘You do not understand. You will forget. The life he led is gone and this new, better life takes its place. He has children. He has a place in the world.’ ‘And the people he saved? The worlds he saved?’ ‘Consequences,’ replied the creature. ‘But we will optimise them also. All will be optimised. The universe will be optimised.’ ‘For you,’ said Lucy quietly. ‘You mean the universe will be optimised for you.’
‘Consequences,’ replied the creature. ‘But we will optimise them also. All will be optimised. The universe will be optimised.’ ‘For you,’ said Lucy quietly. ‘You mean the universe will be optimised for you.’ Without another word, without a moment’s hesitation, Lucy shoved her hand forward again through the icy barrier of the Interface. Passing through it completely, she watched as it transformed into the black, scissor fingered hand of a shadow creature… except for one thing. There, sitting proudly on the pointed finger of her jet black hand, was Lucy’s silver ring. The ring she had been given long ago, during her first encounter with alien life, by a member of her strange extended family. The ring that was so much more than a ring. The ring that had saved her life maybe even more times than Hobo Kostinen. ‘Ha,’ said Lucy. ‘Didn’t count on my bling, did you? The creatures eyes opened from slits to wide open circles. Here, on this side of The Interface, there was nothing to show through form behind them as there had been before. There was only the void, the great black void, a place where things that didn’t exist howled and raged against their nothingness.‘ You’re not from around here, are you?’ asked Lucy. ‘Hobo nailed it. He said you weren’t there. That’s the point isn’t it? You’re not there. You’re not there because you’re not supposed to be and you need to change things in our universe until it’s just right for you.'
‘We call it The Interface,’ replied the creature. ‘From here, we can optimise.’ Lucy thought the thing looked more real here, more three dimensional, until she realised with a start that it was in fact her that had flattened out. She turned her hand back and forth in front of her face, marvelling at the strange elongated flatness of it. Her fingertips brushed something in front of her, something invisible that felt like ice cold water. The world beyond The Interface rippled, the same way that the ship had rippled around her. The way it had rippled around Hobo. ‘Have a care,’ said the creature. ‘The Interface is delicate.’
‘We will… optimise,’ said the creature. It sounded like it was gasping, despite being too flat to possibly have lungs and Lucy realised that wherever the creature’s voice came from, it couldn’t have been from the physical body that it had. Another part of the Interface perhaps.

It's describes it as the universe's canvas, and exists beyond the universe, at the very edge of space-time.

At the very edge of time and space, where our universe ends and there is nothing but the howling emptiness of the Black Void, that thing that is nothing and yet is the canvas on which our reality is painted, there is a place called “The Boneyard”. It is a place where heroes go to die in peace, their victories won and their labours done. There, in the moment between the final tick and the ultimate tock of the clock that measures all time, there is a hope that they might know a small moment of tranquillity and reflect on all the things they have done.
‘Well, that’s because you’re not getting the story in the right order,’ explained The Crone. ‘Let’s start with old shady from earlier, OK? It comes from outside this universe, from the Great Void. It wants to change this universe to make it compatible with itself, so it can enter. So it can take over. That’s what it does.’

Time in the void is essentially a giant loop between the first-last tick (I'll explain later) that resets before one moment can truly move to the next.

That was one of the other things about the Boneyard; everyone seemed to have been here from the beginning, from very first last tick.
The Crone woke up as she always did, right at the tick. Time in the Boneyard was a loop, jumping backwards to the last tick in the fraction of a fraction of a split-moment before the last tock was heard. Everyone remembered what they had been doing, but everything else reset itself and everyone woke up once more just as they had done on their very first day in the Boneyard. The only thing that ever seemed to change was just how long it was between the tick and the tock. Sometimes there was barely enough time to sit up in bed, other times days would go by before the Boneyard and its inhabitants were catapulted backup the timestream.
It had just two numbers, a one and a zero, and a single hand that was moving slowly from the one down to the zero. No matter where you stood in the atrium, you could always see the clock, counting slowly down. The hand was moving quickly today. It would be a short day.

In N-Space, the void is described as a negative space that can't be touched. It contains things that don't exist.

‘It’s not there,’ he said. ‘That’s not an alien. It’s some sort of negative space… it would be like touching a black hole.’
The creatures eyes opened from slits to wide open circles. Here, on this side of The Interface, there was nothing to show through form behind them as there had been before. There was only the void, the great black void, a place where things that didn’t exist howled and raged against their nothingness.

Lucy Wilson banished the Void at the end and beginning of time in The Boneyard, resulting in the Void existing outside space-time (between the first and last ticks of creation) in the first place.

‘What you felt was this,’ explained Lucy. ‘Two rings, but both the same ring, each one trying to protect me from the other. A walking paradox. Just like you, I couldn’t exist. And if I couldn’t exist, I couldn’t be a problem, could I? That’s what you felt.’ The creature staggered backwards, hissing, its arms tapering to sharp points that it raised in front of itself defensively.
Slowly, Lucy began to bring the rings together. They glowed brighter as they moved closer. Above her, the great clock began to shudder. The arm stopped, between the tick and the tock, spasming back and forth.‘ I told you that I’d build you a prison at the end of time and fill it with all people who were like me. I just didn’t tell who the prison was for. I didn’t tell you it was for you.’
‘We have been optimising your universe ready for arrival since the dawn of time. You will not keep us out.’ ‘I already did,’ said Lucy. ‘That’s the biggest paradox of all. I’m the one who casts you out. I’m the one you search for. I’m the one you think is going to help you, and I’m the one who casts you out again.’ Lucy took a step forward, then another, forcing the creature back. ‘Look around,’ she said, ‘There’s a reason I made this place a circle.' The creature, its eyes narrowed to vicious slits, its mouth cracking into row after row of needle sharp teeth, let out an otherworldly howl. It was a sound of rage, and of anguish. It was a sound of infinite loneliness, unbearable jealousy, and endless hunger. It was the sound of the Great Void. ‘You are the void. The void is you. I cast you out now, at the end, and at the very beginning of time. The creature lunged forward, its scissor fingers lancing towards Lucy’s face. Lucy brought the rings together. Two rings, overlapping, merging into each other to form a Moebius loop. The hand of the great clock leapt forward. Tock. Blinding light filled the Boneyard, a light so pure and so white that there was not a single shadow anywhere to be seen.
A plan that it would take until the end of time and back to the beginning again to complete.

Land of Fiction

The Land of Fiction is a void dimension that contains a number of separate lands based on fictional incarnations. For example, the Don Quixote novel, stage play and film would have different sub-realms within the land to separate these incarnations. Its inhabitants are described as 'pseudonomic entities' in Character Assassin.

In Alien Bodies, The Doctor implies the Land of Fiction is at least similar in nature to Mictlan (see Conceptual Space).

‘Yeah, it does. Because – and this is the clever bit – when they took themselves out of reality like that, they put themselves on, y’know, another plane of existence. They kind of stopped being real, and turned into... ideas. Because you can kill a person, but you can’t kill an idea. Get it?’ Qixotl shot a quick glance at the pixscreen. The spaceship was growing larger by the second, its outline slowly filling the sky above the ziggurat. Qixotl hoped the Doctor wouldn’t see it. He’d probably recognise the design, the smug git. The Doctor, however, looked like he was a million miles away. ‘I’m not sure I understand. The Celestis are Time Lords who put themselves into conceptual space?’ His eyes widened, and he slapped himself on the forehead. ‘You mean, like the Shift?’Qixotl squirmed. ‘Erm, well... I’m not really supposed to tell anyone who the Shift’s working for...’‘I see.’ The Doctor nodded. ‘Removal from the material plane. Using the same kind of technology that put the Land of Fiction together, I’d imagine. Ingenious. Totally mad, of course, but... Celestis?’ He was talking to himself now, Qixotl realised. ‘The Celestial Intervention Agency? It’s their level of insanity...’

The Doctor's first encounter with the Land of Fiction chronologically was in The Mind Robber, where the TARDIS drifted in the Black Void until it reached the Land. The Land, similarly, exists outside both N-Space and the Time Vortex. And since the Land is a sort of non-reality that exists outside of reality, none of the laws of space-time have any real meaning in even its individual lands, with The Master being able to traverse the Land by simply imagining them into his telepathic circuits.

DOCTOR: Jamie, Zoe, concentrate only on my words. Think of me. Think of the Tardis. They are the only real things here. Everything else is unreality. It is only in your minds. Now, concentrate. Come to me now. Now! Walk straight to the Tardis. Don't stop!

MASTER: Well, as you see, I'm no longer young, where as you, Doctor, are ageless. You exist outside the barriers of Time and Space.

Fyi, the Master is the Master of the Land of Fiction, not The Doctor's similarly named arch-rival, The Master.

The Master states that the Land is beyond Dalek science and the thought processes of battle computers that think in 5-dimensions (a term, again, often used for the Vortex itself). This definitely refers to the fact that Daleks literally don't have the imagination necessary to perceive fictional characters like Medusa, but the fact that The Master applies this to battle computers (which are literally humanoid-interface computers designed to compensate for the Daleks' hideous lack of imagination) strongly implies that the realm is both transcendent of and outside the Time Vortex.

It's also worth noting that the Land of Fiction's fictional mathematics can affect 'matter' within the Land itself.

Upon entering the Land of Fiction, the Daleks describe the void itself as a sub-dimension with infinite boundaries, yet zero mass, structure or energies, which is consistent with Dracula's description in Legend of the Cybermen. Notably, sub-dimension is also the same language used to describe the Land in Conundrum and Head Games. However, the realms within the sub-dimension are finite.

‘A breach has opened,’ the Doctor had explained to his three companions. ‘A semi-natural thing, a fluke accident, perhaps caused by the Timewyrm or by the Monk’s machinations with the timestream. Maybe even Gabriel and Tanith created it as a by-product of their existence. That doesn’t matter. What does is that this phenomenon may have serious repercussions. It has created a gateway between our own reality and a fictional sub-dimension.’

The only exception is the 'endless' planes of TLoF's limbo, where dead/dormant fictions reside until they go insane and die permanently. Even by the Land's standards, things here aren't considered to be as 'real' as the rest of the Land.

The Land is based on all fiction, including radio plays (whose characters only 'truly exist' in the form of voice, meaning their appearances are bound to the listeners' imagination, including the imagination of other fictional characters from visual realms). For reference, The Master collected 'thousands upon thousands' of fragments of a book from Moriarty in most of the Sherlock Holmes universes.

As for the total number of universes, we don't have a definite limit, but we know for a fact that it's not as massive as the totality and possibilities of fiction because A) while different incarnations exist based on interpretation, existing fictions are subject to retcons of their original material, with Zeus and other characters in the Greek dimension displaying certain traits from what authors, like Ovid, have applied to their stories, and B) fictions can can become dormant.

Interdimensional Space(s)

In Reborn and The Axis of Insanity, it's stated that The Axis exists in interdimensional space, effectively nowhere, allowing the Time Lords to ejected countless damaged and truncated alternatives to established history within The Axis before they contaminate the primary timeline; some are minor alternatives, while others are implied to be fully fledged continuums. However, it's also part of the multiverse, as the same portal that lead to The Axis and all of its individual worlds could allow the Daleks to cross the entire multiverse in Extermination.

In Old Girl, the Tenth Doctor believes that it disappeared after the Time War.

All this comes from Preternatural Nights, The Taking of Planet 5, The Brakespeare Voyage, Dead Romance and The Book of the War. I don't have the effort to clarify which is which.

The Ur-Universe, aka De-Sitter space, is a predecessor universe that (given enough time) extends to the point where space-time becomes locally quasi-flat and can no longer express local Einsteinian space-time curvature. As this universe approaches heat death, it gives birth to successor universes. It's also possible (and very likely, given the sheer amount of infinite universes) that this process has occurred time and time again.

Imagine a balloon with an infinite diameter, the apparent curvature of its surface would tend to zero.5
‘No, you need to know this. He watched the secret sea, the outer ocean, the myriad universes that exist outside the bubble of our space-time. Like ours, the end products of the original Ur-universe.’ ‘This is blasphemy. If our Masters knew of this…’
‘Try this. Before our universe, there was another. It expanded almost for ever, until its space-time was locally flat and devoid of matter or gravity. Eventually, pure randomness within the deep-foam structure of its underlying superstrings produced a number of acausal point formations in which parity was invalidated and gross amounts of either matter or antimatter could come into “real” existence. These events, separated by billions of light years of black, flat, emptiness, expanded out, forming bubbles of their own.’ ‘New universes!’ Even under the circumstances Xenaria couldn’t help but be impressed. ‘Yes. Now assume for a moment that our universe is one of these second-generation events. Now maybe within the body of that dying old universe, things that were terribly old had survived for perhaps a googolplex of years after the death of all the cold iron stars. To them the new universes were a threat. An eruption of chaotic, primeval energies. Perhaps they sought to extinguish them. Perhaps they had to.’
The theoretical argument goes like this. The end state of an open1 universe will, given absolutely infinite past time, extend to infinity. 2 Our universe is open.3 Therefore at some future point it will expand to infinity. An infinitely expanded universe will exhibit the following characteristics: zero local Einsteinian space-time curvature4,and little, if any, matter over vast ranges of space-times5. Such an area of space-time can be regarded mathematically as a domain of De Sitter space.6 An empty De Sitter space can be shown to lead without additional causal interaction to the creation of a further universe similar to our own.7 Thus as our universe approaches heat death, it will naturally ‘give birth’ to one, or more, successor universes. As the characteristics required for the formation of a quasi-flat De Sitter domain will be reached within a merely large (but non-infinite) time, it is possible that this process has in fact already occurred, and that our universe is itself a ‘successor’ universe to an older open structure.8
Further, if it has occurred once, it may well have occurred many times and a number (either large or infinite) of universes have come to be and ended, are currently inexistence, and will come into existence after our own. Those universes will themselves expand, either to end as open universes, eventually budding themselves, or as failed closed universes opening out from only to ‘fall back’ to the surface of the original space-time.
It should be noted that these universes are not the quantum universes predicted by the Many Worlds Interpretation of Quantum Mechanics.9 It is therefore theoretically possible that their existence could be detected or that they could be contacted. It is in this theoretical ‘metaspace’ of universes that the Swimmers, in essence, predator universes, exist.
The question as to whether an absolutely infinite time can end is a moot one, many philosophers of mathematics have denied that an absolutely infinite amount of time could exist in the past, since if it did we could never have reached the present. However as a merely large period will produce nearly the same degree of flatness of curvature and absence of matter as an infinite period it is not in fact necessary to demonstrate that this has in fact happened. That said, I consider that the existence of apparent singularity discontinuities at the creation points of each universe would have the effect of making it possible for finite periods of time to he defined within each universe, while the ongoing time of the original, or Ur universe, could be regarded as infinite (or larger) that than within any one successor universe.9 According to which, every action which can be depicted as a mixed state in Quantum Mechanics results not just in the one real result which we see when the mixed state ceases to be a probability field and becomes measurable upon observation, but in every possible result, the others merely happening in different universes. The Copenhagen Interpretation denies the ‘real’ existence of such universes and no theoretical methodology exists by which they could he detected.10 Within the next billion or so years.
There is an expanse between universes - frequently referred to, most notably by the Celestis, as an “ocean” - but it’s an expanse without either time or scale in the conventional senses. Here we’ll once again refer to it as Ur-space, though “space” is yet another misleading term, as nothing can move through it (there’s no distance there to move through). Nonetheless, we can think of universes as being “close” to each other or “far away” from each other, as long as we remember that we’re using these words purely for our own convenience. And since we tend to think about exploration in seagoing terms, we generally use the same terminology as the Celestis and imagine the many universes “floating” on the Ur-space ocean.

In the process, however, a void forms between these universes. It's strongly implied that the Void between universes is the result of proton decay, albeit one so lengthy that iron stars (which are only possible if our current theories of proton decay are incorrect) can exist. This is supported by the fact that Swimmers can be grown in artificially accelerated regions of space-time.

There are substantial areas of starless space: so called ‘voids’ which are surrounded by walls or strings of galaxies. These have been detected by the Hubble Deep Field Programme. While voids may of course be dark matter dense, they may already display the characteristics sought above, and if they do not now, the combined processes of expansion and [possible] protonic decay will certainty work to produce such ‘real voids’ over an infinite (or sufficiently large) timescale.6
In seeking a home, the cohort arrived in the vicinity of the Anvil Stars, a region often thought to have been artificially aged as a result of the War. It’s long been established that at a certain point in its history any given universe will be capable of “spawning” – not in any organic or living sense, but nonetheless budding new, younger proto universes from their mass – and in the Anvil Stars region the cohort was able to observe first-hand the creation of such a budded universe. In doing so they observed that during the calfing process, when the universe-seeds are compressed in areas as small as the outer electron shell of a hydrogen atom, mechanisms existed to weed the seeds and select bud-universes with certain, specific characteristics. Accordingly, the troops were able to isolate a number of the “gardener” devices in a null-time envelope for later study. It was initially assumed that the characteristics favoured by the “gardeners” were those either of the universe before the current universe (in which case the gardeners were devices which had outlived their creators, or possibly even contained them, and had passed through the current universe unharmed to commence sculpting the next) or that they were devices of the future crafted by the Great Houses’ descendents/supplanters (to ensure that successor universes would be ready for their occupancy). However, tests carried out after the eventual return of the cohort showed that the “gardeners” were converting the universe-seeds into something else. They were turning baby universes into proto-Leviathans. Tweaking the intra-nuclear force here, massaging down the universal gravity meta constants there, carrying out cosmetric engineering on a previously unimaginable scale. The practical purpose of an entity (let alone vast numbers of entities) large enough to dwarf the entire Spiral Politic is inconceivable. In Hierarchio’s words; ‘To imagine that our future selves have done this is as little comfort as to imagine that it was done by others. If we did this, then what did we become?’

The Void is literally timeless and spaceless, not just an empty vacuum or something.

‘Agreed,’ said One, and paused. Did you know that there are things that swim in the void between universes, in the void that is neither time nor space, the void in which bounded universes like our own exist like froth on a dark sea? He showed me them. They are vast and terrible. Implacable and ancient. And they are very, very large. Against the oldest of them, universes burst and vanish like bubbles striking a whale. They are the leviathans of space and time. Creatures that make common-or‐garden Chronovores look like tadpoles in a stagnant pond.’
In the Pre-War Era, the Leviathans were considered to be vast-but-unintelligent hyperobjects, and any speculation there had been on the subject amounted to horror stories of one blundering against an inhabited universe, but the horror was distanced in un-space and un-time.
However, other universes are simply separate bubbles of matter and energy cut off from the Spiral Politic by immeasurable stretches of un-space, definitely not the “parallel dimensions” of folklore, and as it’s apparently impossible to bridge the un-space gaps these speculative universes remain utterly irrelevant to the War.
“Manchester was never the end of me, Giles. After you disrupted the ritual I was sucked into the half-formed portal and cast out into the space between dimensions. My metabolic processes ceased in that place, and while on Earth I was close to dying, there I was effectively immortal. I drifted for what felt like years, lost and alone. Eventually I found myself pressed against the very boundary of our universe, with nothing to look at but darkness beyond.

To add to that last quote, in Detained, none of the Class characters aged or needed to it in no-space, no-time.

VOICE [OC]: You are in no time, no space. You will not escape. You will not escape! [...]
MATTEUSZ: Do you know what he meant, no time?
APRIL: We've been taken out of time. We won't age, we won't need to eat, but we'll be here forever.

Parts of the void are so remote that even Leviathans don't inhabit them.

Think of the universe for a moment as having three additional directions (alterward, paraward, and otherward) all at right angles to the ones you know (length, breadth, width and time). This is a tremendous oversimplification, but it may help. Paraward, we find a sheath of histories which are either eternally separate from our own anchored time or which diverge and return to it so far in the past, or so far in the future, as to be – functionally – eternally separate from it in terms of the noospheres of the Great Houses. [...] Alterward, we find those histories which divert, at crucial or innocuous moments alike, from ours. Here are the worlds where a toe goes unstubbed, or a vital battle is lost, where the five hundred and eleventh hair on a sloth in the forest has gone grey in one world, and white in another. [...] A few (the mathematics contains several high order infinities, so the number itself may be high) do not appear to rejoin, either eternally leading outside the ‘time-space’ horizon approachable by a normal time-ship, or curving back in closed loops longer than our normal ships can reach, beyond the futures we can access. We call these alterward space-time entities ‘alternate worlds’. [...] But then there is Otherward. Otherward is Outside. [...] These are universes held on separate ‘branes’ in hyperspace, outside the sheath that contains the paraward and alterward components of our universe. These are beyond the reach of our time-ships, who go mad in the horrors of the void between.
But I know from the Head that I have sailed once by the rules of their Guild only to be forced to abandon The Brakespeare in the great grind of colliding branes, in the hyperpack ice of the Desolations beyond Time, its exploding galaxies firing their flares of radiation into the deep night, in unseen and ineffectual pin pricks against the empty unspace where no Leviathans go.
‘In this case the pilot-ship bond was not enough. Timeships in their natural environments are constantly stimulated by the totality of exterior existence, the signals of the Great Houses, the animal chatter of the subcultures, the syncopated beat of distant quasars. Beyond the Maw there is nothing but abject emptiness. Even the leviathans that swim between the universes move in silence as the radio galaxies embedded in their hides are quelled and smothered by the Great Void. ‘The timeship used in the initial attempt went quite insane after thirty one minutes and, via transference, the pilot was also rendered useless for further non-invasive study.’

Supposedly, if someone was thrown overboard in the Void under normal circumstances, they'd be scattered ontologically.

‘No,’ he said. ‘The Captain is merciful. We simply threw him overboard.’ I had a vision of the old man pitched over the railings, surrendered to the seas between, where time and space have no meaning. He would have been torn to pieces, both physically and ontologically, pulled in all directions in all dimensions at once. Gone in seconds.

The Void is the dimension that exists between universes.

RAJESH: But according to our instruments, the sphere doesn't exist. It weighs nothing, it doesn't age. No heat, no radiation, and has no atomic mass.
JACKIE: But I can see it.
RAJESH: Fascinating, isn't it? It upsets people because it gives off nothing. It is absent.
YVONNE: Well, Doctor?
DOCTOR: This is a Void Ship.
YVONNE: And what is that?
DOCTOR: Well, it's impossible for starters. I always thought it was just a theory, but it's a vessel designed to exist outside time and space, travelling through the Void.
RAJESH: And what's the Void?
DOCTOR: The space between dimensions. There's all sorts of realities around us, different dimensions, billions of parallel universes all stacked up against each other. The Void is the space in between, containing absolutely nothing. Imagine that. Nothing. No light, no dark, no up, no down, no life, no time. Without end. My people called it the Void. The Eternals call it the Howling. But some people call it Hell.
RAJESH: But someone built the sphere. What for? Why go there?
DOCTOR: To explore? To escape? You could sit inside that thing and eternity would pass you by. The Big Bang, end of the Universe, start of the next, wouldn't even touch the sides. You'd exist outside the whole of creation. - Army of Ghosts

It's a 'never-space' composed of and containing nothing, barring its own background radiation.

‘It leads to the Void, I tell you,’ shouted the Doctor. ‘Your readings won’t be accurate, will they? You’re trying to get a reading from nothing. That’s what “void” means.’ He turned towards the glowing gateway and pointed. ‘Look, they’re coming through!’ - Made of Steel
RIVER: So all the cracks in time will close, but he'll be on the wrong side, trapped in the never-space, the void between the worlds. All memory of him will be purged from the universe. He will never have been born. Now, please. He wants to talk to you before he goes. - The Big Bang

DONNA: Cos the Tardis will come back for us. They know that. So if they become completely us, the Tardis will come back for them.
DOCTOR: Is that what you want? Escape?
NOT-DOCTOR: We drifted here, in the lack-of-light, passing no-time. But we would feel it from so far away... your noisy, boiling universe. We want to travel there to play your vicious games and win. - The Wild Blue Yonder

According to Romana, The Void (aka Null-Space) doesn't just exist between dimensions, it exists everywhere and outside of the Vortex. This allowed a Dalek fleet in Homecoming to effectively teleport within the confines of N-Space and totally bypass Gallifrey's rings of spatio-temporal protections, whereas space and Vortex craft would be stopped.

MANTUS: We analysed the Daleks' arrival in the Kasterborous system. We couldn't understand how they bypassed all our defences and alarms. There's a very simple answer. They didn't use the Vortex. [...] They have developed an alternative means of time travel.

Similarly, the TARDIS fell into the Void and bypassed Gallifrey's transduction barrier in The Lost Dimension, even sending The Doctor into Gallifrey's past (which is normally impossible for a Gallifreyan).

In Meet The Doctor, it's stated that the 'Ultimate Void' exists beyond the Vortex, not simply outside. This is supported by the fact that ships can fall out of the Vortex, through the Void, and into parallel universes.

DOCTOR: We fell out of the vortex, through the void, into nothingness. We're in some sort of no place. The silent realm. The lost dimension.

Division operatives have to use conversion technology to maintain their forms within the Void.

AWSOK: Let me show you where we are, Doctor. Here is the universe as you know it. Universe One, if you like. And we are here, outside. The Division. The control centre from which all our operatives were directed. And there, beyond Division... the next universe, and the next beyond that. Multiverses. Our terminology became quaint a long time ago. So here we are, outside one universe, on the cusp of many more. A bridge.

DOCTOR: But the dimensional engineering required to build this place, it's incredible. Oh, conversion! That's why conversion plates allow us to exist in form outside the known universe. - Survivors of the Flux

See Type IV Multiverse - Checks and Balances.

Multiversal travel occurs in the Second Aether.

'Up to their old-fashioned dirty work,' the Doctor said, 'those Antimatter Men. Dipping in and out of the "Second Aether". And my guess is they're probably not the only ones.' He chewed thoughtfully on his pop-tart. 'Someone's messing with the normal rules of energy flow. Time and space are all over the place. Quite literally, I mean. Growing increasingly unstable.'

It's an interdimensional space between the universes of the multiverse. Entire cultures traverse it by utilising flowing energy currents that exist in the realm.

The Second Aether was the realm between space and time where the Famous Chaos Engineers performed their morphing miracles. They called themselves names like The Secondaries or The Preprincipleasures and lived in a dimension not even Morphail's wizard scientists could explain. This environment was thought to be the legendary spaces of the in between, which could be traversed by winding roads of energy and where peoples of every species, race and creed walked between the worlds. To some they were known simply as the Spaces, but to the more romantically inclined, the Second Aether. Home to the totally opposed immeasurable entities generally known as the Spammer Gain and the Original Insect, the Second Aether sheltered many a corsair tribe but in the main the inhabitants left the real fighting, the blood feuding and the empire building to their associates.
The red-brown and yellowish tanker had not been built to run on colour, that mysterious energy leaking through from the Second Aether. But she would repower long before she came anywhere near the Schwarzschild Radius.

It's described as 'another kind of space' than the multiverse, and exists above space-time between the planes of the multiverse and at its centre. The balances of the multiverse don't apply to it.

These were the people who had once mapped the multiverse and discovered another kind of space altogether. This 'other' space was known as the Second Aether. There were stories that the Doctor had actually named the region, but he always denied it.
The Doctor hung somewhere outside space and time, drifting, drifting... He had fallen asleep. He hung above time, above space, and he looked down towards the scarlet expanse that wound into the quaking greenness of Emerald Edge. Here was now and no longer. Here, only the scarlet expanse of Ketchup Cove was stable, the old rendezvous point of the Chaos Engineers. Here were four quasi-planets circling a heavy sun. A star circling a black spot. One place. One time. Into which everything used him as the node. The focus of all the worlds of the multiverse. Stretches of yellow-silver spread everywhere. The so-called moonbeam roads. Summer, Autumn. Everything else was lighter or darker. Sooner or later. Bigger or smaller. This was where it focused and from where it all radiated. And he thought his thoughts, reviewing a million or more options. The Roogalator. The Silver Arrow. Four planets circling a single star. Miggea, Circling a tiny black sun. The time vault. A bucky ball, stronger than any known metal.
'What is, what is, what is, what is...' She drew a deep breath and forced herself to stop. 'The Second Aether? It's the space between. It's where I think we'll find the Roogalater. The Regulator. In that space.' 'Between what?' 'Between everything. Between the First Aether and the Third. Between Law and Chaos. Between Life and Death. Between Matter and Antimatter. Between Dreams and Waking. You name it, Amy...''Me name it? I can't name anything. I don't even know where we are.''I told you.' 'The centre? The centre of the multiverse? The centre of reality? The centre of nowhere? How did we get here?'
The Gargantua was safe for the moment, drifting in the Second Aether, where neither rule nor misrule applied.

It has an illusory effect because everything constantly changes, forcing ships to constantly change with it.

He brandished his sonic screwdriver and winked. Reflected light gave his face a bloody appearance. Then he vanished. Suddenly she was terrified. She had no resources left, no courage, no intelligence, no physical energy. Nothing. She felt that she was buoyed up on water. She was swimming. Doing her best to stay afloat. A mist was rising and there was something coming up under her feet. A ship? No. It was a man. A man she had never seen before. He had a sallow hatchet face with cold, mocking eyes. He wore a crumpled linen suit, a white cotton shirt, a dark blue bow tie and on his head was a white naval cap. At first he seemed to be standing on a small wooden platform but, as he rose up towards her through clouds tinged with pink, she saw tha the was standing on the deck of a small seagoing launch. He raised his hat and held out his hand to help her aboard. 'Good day to you, Missy.' His voice was oddly cultivated, sarcastic. 'Welcome aboard my little ship. Captain Horatio Quelch at your service. What brings you to our part of Creation?'
'Because we're almost out of the Second Aether and we're not designed for it, Amy. Those Second Aether ships survive by constantly changing shape. Adaptation's the name of their game. That's the way they move. Not because they have enemies to deceive but because the rules of time and space are different here. Everything flows, remakes itself, alters its constituents. If, like us, it kept the same appearance the space would essentially harden around it, crushing it. Can't you hear that creaking now? They go with the flow. And look at those prediction charts! We're going to break apart if we stayin this area of space. In our own space-time we can probably limp on to Miggea, or another system if we have to, and get help there. It might be possible to put all the passengers of fand then make a dash back to Desiree, where we could be decently patched up. As it is, we just about have enough food, fuel and equipment to make it to our destination.'

Ghost Worlds are born in the Aether.

The sun was dancing with fiery gasses. She could easily believe, from what little she'd seen of it, that the Ghost Worlds had been born in the so-called Second Aether, in the spaces between each plane of the multiverse.
The Ghost Worlds, as the Miggea system had been called since the discovery of those singular properties, retained their secrets, but there was no doubt at all that they existed against most of the present laws of physics.

Despite existing outside space-time, the Second Aether is filled with a water/gas-like medium.

'The weird thing about the Second Aether is the atmosphere. Because so much is reversed here, any planet you find in the Second Aether will not naturally have any atmosphere at all. The air we breathe is in the space between the worlds. Miggea's a bit of an exception because of the terraforming which went on before they realised what the star and its planets really were. But you can still travel about in the Second Aether as if it were water and breathe it as if it were air while if you landed on an untreated planet you'd need a spacesuit or you'd burst and die.'
That night, the sky became layer upon layer of complementary realities, one fitting into the other, one shade colouring the next, one blazing aura into another and all giving off a faint, distant noise, for sound actually travelled through the space between the worlds of the Second Aether while Miggea's planets had been soundless before the terraforming. Spiralling out in every possible direction and dimension, the tapestry of worlds could scarcely be absorbed by the human senses.

KLOL506 · Dec 26, 2023

Who should I tag for this one?

ByAsura · Dec 26, 2023

Idk. Everyone you can think of, ig.

@Starter_Pack @Colonel_Krukov @Ultima_Reality

Rabbit2002 · Dec 26, 2023

following

KLOL506 · Dec 26, 2023

@DontTalkDT @Executor_N0 @Qawsedf234 @Sir_Ovens @DarkGrath @Firestorm808 @Celestial_Pegasus @Everything12 @Andytrenom @Celestial_Pegasus @Maverick_Zero_X I was asked to tag y'all, IDK any other person who is a Tier 1 expert of this magnitude.

Qawsedf234 · Dec 26, 2023

I really can't comment unless I know what the OP is looking for tier wise.

ByAsura · Dec 26, 2023

Something above High 1-C or High 1-B, frankly. But I'm not sure exactly how high we can get.

Hasty12345 · Dec 26, 2023

Just when I read the OP and thought I was done, there’s 2 monster replies I gotta go through

Tyranno223 · Dec 26, 2023

Tier 1 stuff of this scale is way beyond me, but maybe another post detailing suggestions for tiers would help opinions?

ByAsura · Dec 26, 2023

I don't know enough about it myself.

But I've heard that a Tegmark Multiverse + Set Theory + High Order Infinities + Platonic Form stuff can get 1-A in some cases.

Udlmaster · Dec 26, 2023

ByAsura said:
Something above High 1-C or High 1-B, frankly. But I'm not sure exactly how high we can get.

I think it might be best to segregate what beings fit where in the cosmology and what tiers we think they should be at for the convenience of non-Doctor Who lore nerds.

ByAsura · Dec 26, 2023

Should I move this thread to general discussion, or something?

Doctor Who cosmology is insanely inconsistent, and I don't know enough about our Tier 1 standards to neatly demarcate everything I wrote.

Maskofthedragon · Dec 26, 2023

Oliver_de_jesus · Dec 26, 2023

ByAsura said:
Should I move this thread to general discussion, or something?

Doctor Who cosmology is insanely inconsistent, and I don't know enough about our Tier 1 standards to neatly demarcate everything I wrote.

I don't think it will change much in this case, if you want, do it, but honestly It's more about making everything fit instead of looking for more people.

Hellbeast · Dec 26, 2023

Udlmaster said:
I think it might be best to segregate what beings fit where in the cosmology and what tiers we think they should be at for the convenience of non-Doctor Who lore nerds.

For a start, beings like the Toymaker and Guardians are super high up. The Toymaker claims that "I am the Space-Time Vortex, Doctor" and exists in the Sixfold Realm as the Guardian of Dreams and Crystal.

Hasty12345 · Dec 26, 2023

I’ve read the whole OP and the follow up comments, that being said idk if I’ve adequately processed it all but here’s my current thoughts on the topic.

Firstly, compiling all of this is a feat and a half, absolutely well done and the amount of time and effort that went into this is definitely worthy of praise and then some.

I want to note that the non-linearity of the cosmology and the seemingly brief and 1(ish) off appearances of some of these concepts very well may make finding any solid tier for the cosmology or even certain levels of the cosmology incredibly difficult. That being said, there MIGHT be a way to find an overall tier, not that I’d know how if anything scales to it.

Given the verse has explicitly mentioned the existence of set theory, higher order infinities, mathematics and sciences beyond anything modern humans can think of, the general nature of mathematics as an underlying structure of reality (iirc). Along with statements of every possible universe existing, showings that marvel superhero’s exist within the multiverse indicating these possibilities are or can be actualised, and a direct statement of the verse being a type 4 multiverse, I can get behind the idea the verse could reach tier 0 via every possible universe existing would entail inaccessible cardinal amounts of universes.

Perhaps that’s a pretty wild claim, however, I can also see how a far more conservative scale that’s still in the same vein of reasoning being a couple layers into 1-A via the “several higher orders of infinity” being taken to literally mean aleph 0 through 3 (or something a rather) existing, which would be the equivalent of a layer into 1-A. With maybe one of the voids warranting another layer??

This is just my general thoughts, definitely open and looking forward to hearing other opinions.

Hellbeast · Dec 26, 2023

Also, the Land of Fiction means that the Ragnarok Gods (and thus Sutekh) are pretty easily Tier 1 since the former created the Land as a side project before the latter killed one of them

Greatsage13th · Dec 26, 2023

Lord_Farquaad69420 · Dec 26, 2023

Qawsedf234 said:
I really can't comment unless I know what the OP is looking for tier wise.

Somewhere between hyperversal to outerversal

NHTkenshin2 · Dec 26, 2023

Tl;dr please good sir.

ByAsura · Dec 26, 2023

TL;DR is nearly done.

Hellbeast said:
For a start, beings like the Toymaker and Guardians are super high up. The Toymaker claims that "I am the Space-Time Vortex, Doctor" and exists in the Sixfold Realm as the Guardian of Dreams and Crystal.

Character stuff is Part 2.

Also, I'm the Space/Time Vortex.

Quasar002 · Dec 26, 2023

Hellbeast said:
For a start, beings like the Toymaker and Guardians are super high up. The Toymaker claims that "I am the Space-Time Vortex, Doctor" and exists in the Sixfold Realm as the Guardian of Dreams and Crystal.

With the latest episode, the toymaker must be at the top of the guardians themselves, as they were able to transform them into "dolls." Although the review is only about the cosmology, I believe it has the potential to reach 1-A.

ByAsura · Dec 26, 2023

I think this is serviceable, and I've added some ~~clickbait~~ dimensional tiering.

TL;DR

The Pre-Universe

The Pre-Universe was the previous universe before the big bang/Time Lords.

Depending on the source, the pre-universe was either a structureless, irrational place where magick exists and nothing was constrained by the 'mundane' laws of physics, allowing for infinite possibilities and variety, like suns made of ice cubes revolving around doughnut-shaped planets.

Or, it was a perfect bell-curve where FTL travel was impossible, and time travel and subjective time were totally impossible.

Honestly, given the nature of the Pre-Universe described in sources like Christmas on A Rational Planet, I think that both are equally true.

Higher Dimensions

The number of higher dimensions is dreadfully inconsistent, and sources can alternate between 10 or dozens (High 1-C to 1-B).

Also, they can be presented as entire planes of existence, with explicit superiority over lower dimensions. For example, 4-D beings in some sources perceive 3-D beings in the same way 3-D beings would see a piece of paper.

Additionally, dimensions can have dimensions of their own, like time having an internal 4-D plane in The Space Museum. The function of these secondary dimensions is to support the space-time continuum.

Bernice Summerfield and the Infernal Nexus

The universe is composed of 417 multiverses (equivocal to universes in traditional science fiction), each existing in radically different states and with different laws of physics. For example, there's a multiverse where cause and effect is more of a suggestion, allowing people to fly if they don't think about the mechanics behind it.

These universes and multiverses are, to some degree, composed of an infinite number of dimensional sets that exist at right angles to each other; Bernice describes all 3-D beings from her universe/dimensional set as moving through an extra-dimensional axis, including 3 dimensions of space, and 1 of time, but in actuality, it's 3 dimensions of space and the time of an 'infinite dimensional set'.

Some people believe this means the universe is infinite-dimensional (aka, High 1-B, if superiority standards are met), but I'm personally not sure.

Transdimensional travel between sets/multiverses is akin to how someone can point to the USA from Ireland, but can't simply cross the North Atlantic on foot to get there. It also means crossing completely different timelines.

N-Space

All of space-time can be equivocated to a vast ocean. Part of the ocean is composed of events that are virtually immutable, but most of the ocean is composed of infinite flux and alternatives. For example, a time traveller could travel to 1934 USA and find that Roosevelt is president, but another trip could take them to a version of 1934 where Charles Hughes was president.

All of these flux points exist in the ocean of time simultaneously (in a non-linear sense), but they're eventually weeded out by the Web of Time, which lays down a dominant reality (as in a full continuum, unto itself) based on the aforementioned fixed, virtually immutable events.

To put it into perspective, imagine the universe as a tree. The trunk is established reality, and the branches are all the existing alternatives. Slowly, but surely, particular branches contort themselves to extend the trunk, and the alternative branches cease to exist.

Also, N-Space is composed of mathematics at its most basic, fundamental level. Its physics and philosophy include the Plato's Theory of Forms, Set Theory, Probability Waveforms/Wave functions, and String Theory. Plus, there's a 'secret passage' (more like an extra layer, rather than another dimension) through N-Space that allows for intergalactic, FTL and time travel.

From what I've heard, even if the continuum was simply Low 2-C, this would qualify for Low 1-C.

N-Space's Adjacent Dimensions

N-Space has a number of adjacent dimensions, including Hyperspace (a fourth dimensional space of warped physics and non-Euclidian geometry that exists alongside the 4th dimension), Null-Space (a non-space time continuum that exists as a counterpart to N-Space, allowing humans to cross over after death), Shuntspace (a generic FTL dimension connected to the Vortex), and Subspace (an abstract, poly-dimensional dimension that corresponds to N-Space).

Multiverse

Because time moves sideways, in addition to backwards and forwards, the multiverse contains an infinite and infinitely expanding number of universes, with the numbering explicitly containing high order infinities.

Some (in a relative sense, because it's still infinite) universes have vastly different laws of physics, including universes where cause precedes effect, magic is real, and geometry is non-Euclidian.

To my knowledge, a Tegmark multiverse with an infinite and infinitely expanding number of infinite-dimensioned universes that have laws of set theory is 1-A. I'm not sure what it'd be if the universes were just Low 2-C, Low 1-C, Low 1-B, or 1-B, though.

Space-Time Vortex

N-Space's space and time can interact in a non-Euclidian fashion and manifest on a separate, higher plane of existence, creating the multi/poly-dimensional Space-Time Vortex (which is composed of both raw, flowing time, and non-space, non-time). The Vortex supports the space-time continuum, which is roughly the size of an 'average singularity' by comparison to the explicitly infinite Vortex. It also leads to every point in space-time, including the ocean of fluxes, and contains events that don't exist.

Other aspects of the Vortex include Hyperspace and Interstitial Time, which is the time that exists between 'now and now', essentially meaning that it's outside of all space-time ('everywhere, nowhere' and 'everywhen, nowhen') and contains geometries and colours too complex for the normal universe.

While certain aspects of the Vortex's nature can be described mathematically, it's explicitly impossible to describe the Vortex in normal mathematical or physical terms.

Different universes also have their own Vortices, with different laws of physics; even in near-identical parallel universes, space-time is different enough that using it to power a TARDIS is like putting diesel in a petrol engine.

The multiversal Time Vortex supports all universes, and is so large that the multiverse could simply fall into the Vortex and cease to exist. In fact, a rip in the axis of the Vortex lead to other multiverses.

The Black Void

In most sources, the black void is the spaceless, timeless empty void that preceded N-Space's big bang; it's more akin to a hole in reality than a reality itself. TARDISes—designed to traverse the Vortex and realspace—break up in this region because it's 'outside' of the universe.

The Land of Fiction

The Land of Fiction is an infinite 'sub-dimension' that The Doctor accessed by drifting through the Black Void. It's outside reality and the Space-Time Vortex like the Black Void, and The Master implies that it surpasses 5 dimensional thinking (referring to the Space-Time Vortex).

The Land is the culmination of most of human fiction, such as Greek Mythology. These Lands are finite, besides the Land's version of limbo (where dormant and destroyed fictions reside).

There's no time or actual physics within the Land, and the laws/principles are determined by imagination.

Omniverse

The omniverse is a collection of multiverses. We don't have explicit proof that there's an infinite number, but the actual number is implied to be far larger than something like 2.

The Six-Fold Realm

According to a few sources, there's 11 dimensions. The lower 5 dimensions ejected the upper 6 after the Big Bang, creating a Six-Fold Realm of conjoined but separate higher dimensions that knot through space-time and the Time Vortex, giving them 11 spatio-temporal dimensions.

The interaction between the SFR and 'Higher Place' created an 11th dimensional, quantum lattice of pin-point singularities across the entire multiverse called the Lux Aeterna (aka, the 'quantum foam'). This lattice purportedly exists at the heart of the SFR, but sources are inconsistent as to whether the SFR exists above N-Space or the entire multiverse.

Void Between Universes

The Void is a dimension between universes that contains no quantum activity, including space, time/retrocausality, matter or energy, besides its own background radiation. It can be described as a 'never-space'. It exists outside and beyond the Space-Time Vortex.

We don't know if it exists between all multiverses, but Aswok Tecteun does mention multiverses in some relation to it.

Hasty12345 · Dec 26, 2023

Based on this summary, I think the cosmology could be tiered as follows:

ByAsura said:
Bernice Summerfield and the Infernal Nexus

2-A, possibly high 1-B

This is tricky, as it could be high 1-B based on this summary, however, whether or not it's high 1-B or 2-A doesn't make a difference to the overall cosmology tier, just the "Universe" tier. afaik, an infinite amount of perpendicular dimensional axes would be high 1-B, even if universes are arranged to only occupy 3 or 4 at any given moment.

ByAsura said:
Higher Dimensions

1-C to 1-B based on however many higher dimensions. If these higher dimensions pertain to the universes that are aligned on the (possibly) high 1-B axes, then honestly, it could just be a matter of the speaker's knowledge as to how many dimensions there are, as the Infernal Nexus would technically allow for the universe to occupy upto infinite dimensions. I'll leave it to you and other knowledgables to determine whether or not there are hard contradictions or if the statements come from characters who are limited in their understanding of the cosmology at the time etc

ByAsura said:
The Pre-Universe

No idea. if this is a space that could be interpreted as the "landscape" in which the "Universe" mentioned above is, then it stands to reason barring any contrary evidence that it's around the same size as the "universe"?

ByAsura said:
N-Space

This would depend on the above, I agree that it seems like a higher dimension to what it encompasses.

If the Universe is 2-A, then low 1-C
If we say N-Space encompasses the higher dimensions, it's whatever dimension we decide on +1
High 1-B, then N-Space could be low 1-A depending on how we treat that jump, iirc we currently treat it as the difference between aleph null and aleph 1?? If so, idk if the logic that would make it 1-dimensional jump would justify the jump from high 1-B to low 1-A, or if it would just be higher into high 1-B.

ByAsura said:
Multiverse

ByAsura said:
Because time moves sideways, in addition to backwards and forwards, the multiverse contains an infinite and infinitely expanding number of universes, with the numbering explicitly containing high order infinities.

Based solely on this quote alone, I'm inclined to put the multiverse at 1-A irrespective of how large the universes are. That is because even an aleph 2 amount of universes would equate to a aleph 2-sized cosmology which is currently 1-A, and the specific quote mentions several higher order infinities that would imply at least more than 2 above aleph null.

(in Ultima's new system, should it be implemented, however, it would not reach 1-A as far as I understand it, as it would still be a quantitative cosmology)

ByAsura said:
Space-Time Vortex

This might sound like absolute wank, but in a verse where human mathematics is less than equivalent to hitting rocks together (with explicit comparisons to general relativity and set theory), being larger than a multiverse that's several higher-order infinities larger than infinity I fail to see how tier 0 isn't an actual reasonable possibility for such a structure with such in verse context. I don't know how we handle such a structure, it's far beyond my understanding of the tiering system.

And with that my ability to quantify the cosmology kind of breaks down here. The next structure that supersedes the multiverse and apace-time vortex seems to be the omniverse, which would just be larger but not necessarily a higher layer than the multiverse. With the next couple of structures seeming to be below the multiverse, so they might fit in somewhere else?

Oliver_de_jesus · Dec 26, 2023

Later I will give my opinion, I will need all my mind to give a solid opinion and remember certain things

Hellbeast · Dec 27, 2023

Hmm I see

Who are the best minds in the wiki for Tier 1 stuff?

ProfectusInfinity · Dec 27, 2023

Hellbeast said:
Hmm I see

Who are the best minds in the wiki for Tier 1 stuff?

Knowledgeable Members List (Wiki Terminology)

This page is intended to be a list of various categories of expertise important to this wiki that frequently require experienced evaluations, as well as a list of members who think that they are highly knowledgeable regarding them. Staff and experienced members who consider themselves to have a...

vsbattles.fandom.com

DontTalkDT
Executor N0
Ultima Reality
Elizhaa
PrinceofPein
Agnaa (Only knowledgeable in the theoretical standards, not the practical application of which verses qualify)
Everything12
TheUnshakableOne
Ovy7 (Not that knowledgeable on the math/set theory side)
Rakih Elyan
IdiosyncraticLawyer
RatherClueless

Lord_Infinit · Dec 27, 2023

So, the glory would be High 1-A/ 1-A?

Hasty12345 · Dec 27, 2023

Lord_Infinit said:
So, the glory would be High 1-A/ 1-A?

We’re trying to figure it out

Oliver_de_jesus · Dec 27, 2023

These are my thoughts on everything, that is, how I interpret cosmology, , it's not long, I had to reinvent it 3 times and eliminate part because I thought it would be confusing

N-Space/Gallifrey Noosphere/Time Web

Space N is the base universe, it must be taken into account that threatening space N can range from 3-A or Low 2-C, since there is a difference in the continuity of both, as Asura indicates, the Web is a map of infinities. possibilities of the conventional universe, which expands in all possible directions in all aspects, with its only limit being that they have a life span, its uncountable infinite branched timelines ad infinitum, a Low 1-C structure.

By the way, wave functions are at best something to add more credibility to the ocean of time as a structure that allows countless potential moments of time to exist until the present decides which one is true, since collapsing the wave function in In this case a fixed point is created.

Given mathematics and Plato's things, where it is said that the true structure of N-Space is what defines how the dimensions of time work and how everything develops, such as 11 dimensions of N-space are mathematical structures that the Time Lords built to allow their Tardis to move and create their barrier (transduction barrier) that covers Gallifrey as the focal point of the Web but also exists outside to some extent.

Even without the Adjacent Dimensions of N-Space, the Web of Time in its absolute entirety is High 1-C to low 1-A.

Very Fabric of Time is the clearest demonstration that the conceptual space of N-space is outside physical N-space itself. I think this also explains how Time Lords can open or close rifts with other universes during the time war.

Adjacent dimensions of N-Space

Shuntspace does not appear to be one of the many layers of the Vortex, probably one of the upper layers (as explained in QA, Vortex has levels, I assume Shuntspace is somewhere between N-space and Vortex)

Null space, if I understand correctly, seems to be the other side of the coin (N space), so the maximum you could get would be 2-C low for not being in regular spacetime.

The subspace could be 1-B, since we take conventional Euclidean directions to be something flat like two dimensions or a three-dimensional cube.

After tentatively emerging into reality, the funnel stiffened; it immediately grabbed trillions of tonnes of core matter –superheated plasma – in its poly-dimensional folds and pleats, before twisting in countless directions, none of them even slightly Euclidean.

The directions part would indicate that it involves multiple axes outside the conventional width, depth and height.

Pre-universe

My opinion on the Pre universe in terms of the Tier of the wiki is simply Low 1-A, given how it is represented, as something without structure, where each configuration of the laws not only of physics (in the where it says broke the laws of nature, or the laws of physics, or the laws of time, or laws there weren't even names for), but that any configuration was possible in the pure state of the Pre universe

Higher Dimensions

Honestly, while the number usually varies, I believe that they are true mathematical spatial dimensions, still coordinates and the beings of these are represented as incapable of remaining in these due the size of lower planes or being able to move as they want, for example an Eternal could walk to move through time.

Time Vortex

Time Vortex is as such the terrain on which the WoT was built, of course, there are much deeper sections but ultimately both scale to the same level, I personally believe that destroying the Vortex without the addition of parallel universes should scale to the entire N-Space cosmology, since it stops just when the universe stops..

Multivese (Spiral Yssgaroth, E-space, etc)

Honestly, I believe that E-Space has a nature that allows it to scale to N-space because of how it is used as a filter to allow the regular universe to not collapse due to entropy, so it will eventually reach the size of N-Space or perhaps it will surpass it since it did not collapse even though N-space exceeded its useful lifespan several times and there are still stories where it is represented as something essential

Spiral Yssgaroth is as ByAsura describes, a conscious space-time of its own that is against the laws of time, however unlike E-space or another universe, they are not simply one is red and the other is blue, I think it is similar to one being matter and another being anti matter,

To put it in perspective of how each one is located, I think that N-space is the earth, E-space is the moon, however Yssgaroth is another planet that orbits the earth, this planet constantly seeks collision with the earth but because the time lords created the Web as a barrier, this causes "gravity" to prevent them from colliding

Full E-Space scale to N-Space

The rest of the multiverse exists in all possible configurations, from real higher dimensions, being able to contain the Post universe that have 27 Dimensions in the future, through the type 4 multiverse and the MWT, so I buy it to be Low 1-A as minimun

Six-Fold Realm

SFR should scale above the Time Vortex, removing the fact that it has an extra layer, I interpret that the reason the 6 dimensions lost against the 5 was because the Time Lords somehow created a paradox that allowed this during the event 1, in fact going back before the time lords played with creation is equivalent to going back before the big bang that is due the tardis can literally move before the big bang, which would not be possible since the Tardis has a limited range until how far it can go forward or backward.

The TARDIS engines groaned once, loudly, and then were silent.'We are here,' said the Kin. Its Amy Pond mask was now just a flat scrawled drawing of a girl'sface.'We're here at the beginning of it all,' said the Doctor, 'because that's where you want to be. ButI'm prepared to do this another way. I could find a solution for you. For all of you.''Open the door,' grunted the Kin.The Doctor opened the door. The winds that swirled about the TARDIS pushed the Doctor backwards.The Kin stood at the door of the TARDIS. 'It's so dark.'

'We're at the very start of it all. Before light.''I will walk into the Void,' said the Kin. 'And you will ask me, "What time is it?" And I will tellmyself, tell you, tell all Creation,
Time for the Kin to rule, to occupy, to invade
.
Time for theUniverse to become only me and mine and whatever I keep to devour. Time for the first and final reign of the Kin, world without end, through all of time.
''I wouldn't do it,' said the Doctor, 'if I were you. You can still change your mind.'The Kin dropped the Amy Pond mask on to the TARDIS floor.It pushed itself out of the TARDIS door, into the Void.'Doctor,' it called. Its face was a writhing mass of maggots. 'Ask me what time it is.''I can do better than that,' said the Doctor. 'I can
tell
you exactly what time it is. It's no time. It's Nothing O'Clock. It's a microsecond before the Big Bang. We're not at the Dawn of Time. We're before the Dawn.'The Time Lords really didn't like genocide. I'm not too keen on it myself. It's the potential you'rekilling off. What if, one day, there was a good Dalek? What if …' He paused. 'Space is big. Time is bigger. I would have helped you to find a place you could have lived. But there was a girl calledPolly, and she left her diary behind. And you killed her. That was a mistake.''You never even knew her,' called the Kin from the Void.' She was a kid,' said the Doctor. 'Pure potential, like every kid everywhere. I know all I need.'The squiggly whatsit attached to the TARDIS console was beginning to smoke and spark. 'You're outof time, literally. Because Time doesn't start until the Big Bang. And if any part of a creature thatinhabits time gets removed from time … well, you're removing yourself from the whole picture.'The Kin understood. It understood that, at that moment, all of Time and Space was one tiny particle, smaller than an atom, and that until a microsecond passed, and the particle exploded, nothing could happen. Nothing
could
happen. And the Kin was on the wrong side of the microsecond.Cut off from Time, all the other parts of the Kin were ceasing to be. The It that was They felt theash of non-existence sweeping over them.In the beginning – before the beginning – was the word. And the word was 'Doctor!'But the door had been closed and the TARDIS vanished, implacably. The Kin was left alone, in the Void before Creation .Alone, forever, in that moment, waiting for Time to begin.

-Nothing O'Clock

Omniverse

Created from each interaction, where infinite multiverses exist and continue to grow through the growing tree of possibility, this can be 1-A since it is an infinity upon another infinity

TLoF

we can give this Low 1-C (6D), given that it exists as unlimited and beyond Dalek science and the thought processes of battle computers that think in 5-dimension.

Void stuff

Dark Void scaling to the entirety of Vortex/WoT, as it is described as the space where existance stop and still being larger regardless of the fact that Vortex/WoT is infinite

The void/Ur-space demonstrates that, even in the infinity of creation, even with all possible combinations of birth, the universes remain separated by a barrier of immeasurable timeless and dimensionless distance.

ByAsura · Dec 27, 2023

I think we're dishing out certain ratings, particularly 1-A, a little too easily here.

Oliver_de_jesus · Dec 27, 2023

ByAsura said:
I think we're dishing out certain ratings, particularly 1-A, a little too easily here.

?

So what ratings would you like to say?

I mean, the part where I said the N-Space (in its absolute entirety) being High 1-C to low 1-A, refers to two extremes, one low end and one high end

Hasty12345 · Dec 28, 2023

ByAsura said:
I think we're dishing out certain ratings, particularly 1-A, a little too easily here.

1-A is not hard to get for verses that incorporate basic set theory into the cosmology.

It’s a flaw in the tier system it I’m being honest. If we take your summary of the cosmology to be accurate, a multiverse having universes numbering in the range of “several orders of higher infinities”, the verse meets the current definition of 1-A. I don’t think it’s a matter of “handing out 1-A too easily” the verse as described meets the definition almost to the literal letter.

ByAsura · Dec 28, 2023

It's really that easy?

Hasty12345 · Dec 28, 2023

For math based cosmologies it can be.

However, if Ultima’s new tier system gets implemented, I don’t think what’s been presented could reach the new 1-A. But as it currently stands, I do think there’s grounds for 1-A multiverse based on several levels of higher order infinities worth of universes with the further context of set theory being mentioned, Time Lord mathematics being potentially billions of years more advanced and direct confirmation of doctor who being a type 4 multiverse.

Might be worth calling Ultima or Agna and directing them to your summary to see if they can weigh in. I’m mostly confident in my understanding of the tiers up to 1-A so I do think what I’m saying is correct, but I absolutely could be wrong.

all this aside, is the sixfold realm supposed to be transcendent of the multiverse, I’m a little confused on its place within the cosmology?

Lord_Infinit · Dec 28, 2023

should we ping ultima then?

Lord_Infinit · Dec 28, 2023

btw @ByAsura in the second part you will address the haxs of Time Lords and other races?

ByAsura · Dec 28, 2023

That'll be part 3.

Making Doctor Who Great Again Part 1 - Cosmology/Tiering

Introduction​

Bernice Summerfield and the Infernal Nexus​

Higher Dimensions​

Examples​

Inconsistency​

The Pre-Universe​

N-Space​

The Ocean of Time​

Platonic Forms​

Mathematics​

Conceptual Space​

Warp Space​

Miscellaneous​

N-Space's Adjacent Dimensions​

Null-Space​

Shuntspace​

Subspace​

Type IV Multiverse​

A Brief Explanation/The Very Fabric of Space-Time​

Number of Universes​

Time and Distance/Thin Time​

The Scientific Secrets of Doctor Who/Arthur's Dimension​

Gateways​

Bubble and Brane Cosmology/Wildthyme in Purple/Expanding Universes​

Checks and Balances​

Spiral Yssgaroth​

Exo-Space​

The Word Lord Dimension & UNIT: Dominion​

Space-Time Vortex​

Universal Vortices​

N-Space's Vortex​

The Multiverse​

Omniverse​

Spiral Scratch​

The Glorious Dead​

Marc Platt's Cosmology & The Music of the Spheres​

The Six-Fold Realm​

Voids​

Black Void​

Land of Fiction​

Interdimensional Space(s)​

TL;DR​

The Pre-Universe​

Higher Dimensions​

Bernice Summerfield and the Infernal Nexus​

N-Space​

N-Space's Adjacent Dimensions​

Multiverse​

Space-Time Vortex​

The Black Void​

The Land of Fiction​

Omniverse​

The Six-Fold Realm​

Void Between Universes​

Similar threads

Introduction

Bernice Summerfield and the Infernal Nexus

Higher Dimensions

Examples

Inconsistency

The Pre-Universe

N-Space

The Ocean of Time

Platonic Forms

Mathematics

Conceptual Space

Warp Space

Miscellaneous

N-Space's Adjacent Dimensions

Null-Space

Shuntspace

Subspace

Type IV Multiverse

A Brief Explanation/The Very Fabric of Space-Time

Number of Universes

Time and Distance/Thin Time

The Scientific Secrets of Doctor Who/Arthur's Dimension

Gateways

Bubble and Brane Cosmology/Wildthyme in Purple/Expanding Universes

Checks and Balances

Spiral Yssgaroth

Exo-Space

The Word Lord Dimension & UNIT: Dominion

Space-Time Vortex

Universal Vortices

N-Space's Vortex

The Multiverse

Omniverse

Spiral Scratch

The Glorious Dead

Marc Platt's Cosmology & The Music of the Spheres

The Six-Fold Realm

Voids

Black Void

Land of Fiction

Interdimensional Space(s)

TL;DR

The Pre-Universe

Higher Dimensions

Bernice Summerfield and the Infernal Nexus

N-Space

N-Space's Adjacent Dimensions

Multiverse

Space-Time Vortex

The Black Void

The Land of Fiction

Omniverse

The Six-Fold Realm

Void Between Universes