The theoretical argument goes like this. The end state of an open[1] 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 curvature[4], and little, if any, matter over vast ranges of space-times.[5]
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 in existence, 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 approach of a Swimmer to a ‘normal’ universe could exert a force analogous to gravity between the universes accelerating its expansion in the way detected by Perlmutter & Schmidt (see footnote 3). We may, therefore, conclude that our space-time may shortly[10] impact another.