Another thing I was thinking about was the multiverse and the question of whether the universe is infinite. Lemme start with the universe being infinite.
I mean infinite in size. There's this question about whether we live in a finite closed universe, an infinite open universe, or a flat universe that may be closed or open, but probably open. If the universe is closed, then it should have some curvature. To use an analogy, the surface of the earth has a finite area, but you can walk in any direction and never reach the edge because it curves around on itself. You'd just end up back where you started if you walked in a straight line. The same thing would be true in a finite closed universe. Even though it has a finite size, you could travel in any direction and never reach the edge because there isn't one. It's trippy but true.
Some astrophysicists or cosmologists or whatever tried to figure out if the universe had any curvature. They found that it appears perfectly flat. But there's a margin of error involved that still makes it possible that it's open or closed. Again, using the earth as an analogy, the earth looks flat if you're standing on it because it's so big, but if you zoom out, it's actually round. You can't see the curvature when you're standing on it because the earth is too big. In the same way, the universe could have a curvature, but since it's so big, and we can only see the observable part of it, it appears flat.
From what I've heard, if you take the lower end of the error bars, the smallest the whole universe could be is about 200 times the size of the observable universe. The observable universe is 93 billion light years in diameter, so 200 times that is a crazy big universe. That's the smallest it could be given our measurements of its curvature.
But let's suppose the universe is infinite. If that were the case, would a multiverse be possible? I don't know. There are different models of multiverses. In most of them, they either branch off of each other, or they come out of the same cosmic inflation, so they exist sorta kinda in the same spacetime realm. But in other models, they are completely distinct from each other, existing in separate spacetime worlds with literally nothing between them. It seems like a multiverse of this second kind would be possible even if the univesre were infinite in size, but it's a trippy thing to think about. You want to imagine their location in relation to each other, but if they are their own distinct spacetimes, then they don't have any spacial relation to each other at all. Try to wrap your mind around that.
However, if bubble universes are just local areas of space where inflation stopped or slowed way down, then it's not possible for the universe to be infinite in size since that would cause all the universes to overlap. In the inflationary model, the bubble universes never touch because the inflationary space between them is expanding so much faster than the bubble universes themselves.
This made me wonder whether it might be possible to falsify the inflationary multiverse model just by measuring the curvature of space. If space really is flat or if it's open, then that would seem to rule out the inflationary multiverse model.
I'm not totally sure, though. In the inflationary model, do the bubbles each need to be closed? Do they need to curve in on themselves? I don't see why they would.
But if they don't necessarily curve in on themselves, that means our measurement of the curvature of space doesn't necessarily mean our local bubble is 200 or more times the size of the observable universe. The edge of the bubble could be just beyond the observable region even if the universe is perfectly flat.
I'm not sure, though, because I don't know the physics well enough. But I am curious what you think about whether an infinite universe would rule out a multiverse. If not, how could they co-exist? How could there be other universes if this one were really infinitely big in every direction?
No comments:
Post a Comment