That is often seen as the lowest level of the multiverse and parallel universes.
I suspect that the multiverse includes universes with different laws as well as extensions of our universe.
I am pretty sure it is expanding. As far as I know, the universe is not expanding into anything, it is expanding into nothing.
I'm less convinced that it underwent superluminal inflation when it was very young (there is a fair amount of evidence that it did, but not conclusive evidence).
Cosmic laws such as the speed of light remaining cost to all observers seem to be valid throughout the universe, but we really don't know yet if that was true in the earliest seconds.
Distant parts probably are, but we can't see them when they are or after they do.
In contrast, "inflated" parts are currently visible.
Inflation is one of the not-to-unreasonable possible answers to why the universe is as smooth as it is on large scales.
I do not believe it or disbelieve it, having insufficient evidence to reach a conclusion.
Space itself expanding explains the increasing redshift with distance, but I agree that it is not the only way to look at it.
I know of no evidence that the universe is contracting at large scales.
In contrast, there is considerable evidence that the universe is expanding at large scales, and some evidence that the expansion is accelerating (although another possibility is that type I supernovas were different at different times due to the different chemistries of the stars from which they formed).
Everything that can exist always exists, and the set of all things that can exist should properly be called the Omniverse. However we do not know whether what can exist forms a continuum, in which case the multiverse is the same as the Omniverse, or whether existences cluster, in which case our local cluster is the multi-verse and the set of all clusters is the Omniverse (and there may be levels of hierarchy in between).
If space-time goes on forever, then it must start repeating at some point, because there are a finite number of ways particles can be arranged in space and time. So if you look far enough, you will encounter another version of you— in fact, infinite versions of you. Some of these twins will be doing exactly what you're doing right now, while others will have worn a different sweater this morning, and still others will have made vastly different career and life choices. Because the observable universe extends only as far as light has had a chance to get in the 13.7 billion years since the Big Bang, the space-time beyond that distance can be considered to be its own separate universe. In this way, a multitude of universes exists next to each other in a giant patchwork quilt of universes.
The multiverse theory I might subscribe to is a different flavor than the classic "every observation causes a splitting" nonsense.
A multiverse solves the fine-tuning problem, and makes sense of quantum mechanics (both the apparent randomness, and the spooky action at a distance).
Regarding multiverse theory, I am not a fan of the version that says that the universe splits every time you measure a probabilistic outcome. That is even more a case of the tail wagging the dog than the classical quantum theory that says that the wave function collapses when it is observed.
By multiverse I mean a Multiverse where everything that can exist always exists.
In that case all possible outcomes always exist and when you make an observation or measurement you are merely determining which thread within the multiverse this particular thread of your consciousness finds itself on. Consider two entangled photons where they will be guaranteed to have opposite spins but quantum mechanics says their spins are not predetermined. In my version of multiverse theory, entanglement makes total sense – if you measure one photon and find out that you are in a universe where it is spin up, of course in that universe the other one is spin down – no spooky action at a distance needed all.
Mathematically this produces the same results as classical quantum theory so there is no physical evidence for or against it relative to regular quantum theory. However it explains anthropocentric fine tuning, the probabilistic nature of quantum mechanics, entanglement, and wave function collapse all with a single mechanism that provides logical, intuitive explanations rather than needing ad hoc assumptions, so in that sense it is simpler than the other theories that produce similar mathematical results.
