The problem with this, in my opinion, is A. that we don't make distinctions with multiverse types, and B. that we gauge all multiverses to have the same structure. The way we currently treat
2-C to
2-A is an amalgamation of Type II multiverses (Different universal bubbles created through chaotic inflation) and Type III, which typically represents the Many Worlds Theory interpretation in quantum mechanics (not to mention also including string multiverses in that equation, although that's generally made
High 1-C or
Low 1-B). The thing is, the composition for inflationary bubbles and quantum branches are completely different (It says they have the same features below, but that doesn't cover that a quantum branch is fundamentally different than an inflationary bubble). It's not possible to physically travel between two universes in a bubble universe without a mechanism, and a quantum multiverse is even more tricky, as it would likely require dimensional travel of some degree. According to Wikipedia:
Level II: Universes with different physical constants
Bubble universes ― every disk represents a bubble universe. Our universe is represented by one of the disks.
Universe 1 to Universe 6 represent bubble universes. Five of them have different
physical constants than our universe has.
In the
chaotic inflatio theory, which is a variant of the
cosmic inflatio theory, the multiverse or space as a whole is stretching and will continue doing so forever, but some regions of space stop stretching and form distinct bubbles (like gas pockets in a loaf of rising bread). Such bubbles are embryonic level I multiverses.
Different bubbles may experience different
spontaneous symmetry breaking, which results in different properties, such as different
physical constants.
Level II also includes
John Archibald Wheeler's
oscillatory universe theory and
Lee Smoli's
fecund universes theory.
Level III: Many-worlds interpretation of quantum mechanics
Hugh Everett III's
many-worlds interpretatio (MWI) is one of several mainstream
interpretations of quantum mechanics.
In brief, one aspect of quantum mechanics is that certain observations cannot be predicted absolutely. Instead, there is a range of possible observations, each with a different probability. According to the MWI, each of these possible observations corresponds to a different universe. Suppose a six-sided die is thrown and that the result of the throw corresponds to a quantum mechanics
observable. All six possible ways the die can fall correspond to six different universes.
Tegmark argues that a Level III multiverse does not contain more possibilities in the Hubble volume than a Level I or Level II multiverse. In effect, all the different "worlds" created by "splits" in a Level III multiverse with the same physical constants can be found in some Hubble volume in a Level I multiverse. Tegmark writes that, "The only difference between Level I and Level III is where your
doppelgängers reside. In Level I they live elsewhere in good old three-dimensional space. In Level III they live on another quantum branch in infinite-dimensional
Hilbert space."
Similarly, all Level II bubble universes with different physical constants can, in effect, be found as "worlds" created by "splits" at the moment of spontaneous symmetry breaking in a Level III multiverse. According to
Yasunori Nomura,
Raphael Bousso, and
Leonard Susskind, this is because global spacetime appearing in the (eternally) inflating multiverse is a redundant concept. This implies that the multiverses of Levels I, II, and III are, in fact, the same thing. This hypothesis is referred to as "Multiverse = Quantum Many Worlds".