One theory is that one universe comes out of another. Stephen Hawking has even suggested that blacks holes cause a new universe to form. Once matter is crushed into no existence by a black hole, it more or less becomes matter in another universe. So would there be infinitely many universes, each inside another one, with no real first universe? Or are there a finite number of universes? That’s what’s not clear to me about this theory.
Well, is our universe finite or infinite? If our universe is infinite, it probably has an infinite number of black holes, and so there would be an infinite number of other universes spawned just from our universe.
If our universe is finite though, then the number of black holes in our universe is finite, and so the number of universes spawned from our universe is finite.
It’s an open question whether our universe is finite or infinite, but it is true that even if you could travel at the speed of light forever you’d never reach the end of the universe or return to your starting point, so it’s at least that big
The theory is that our universe is finite and spawned from another universe’s black hole. Even if all universes are finite in size there can be an infinite number of universes. It would just mean that one universe came from another which came from another which came from another etc and you could go back forever.
But just because we were spawned from another universe’s black hole, why would that mean we must live in a finite universe?
I heard an idea once (maybe Lee Smolin?) suggesting that:
a) if universes are born from black holes;
b) and they inherit basic parameters from the mother universe, with small variations
that this would imply that:
a) universes in a multiverse would ‘evolve’;
b) and the most prolific universes would be favorable to black hole formation;
c) and the most common universes would be favorable to black hole formation.
If the most common route of black hole formation is through star formation, this would imply that star-forming universes would be a common type of universe. If star-forming universes are relatively favorable to supporting life, this would lessen the need for anthropomorphic arguments to explain how we came to luck out into this lovely place.
This is kind of pie-in-the-sky speculation, and I don’t think there is any real support for it. I haven’t seen the notion expressed in years, and there may be reasons to think it’s not a great idea at all (although I love the idea from an untrained aesthetic viewpoint).
As BBB says above according to Smolin’s “fecund universes hypothesis”, those Universe that are ‘fit’ (in a Darwinian sense) will spawn more Universe. Whether there are an infinite number is probably left open to question I’d guess. It’s all very speculative though.
Brian Greene’s The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos talks about the nine mathematically and conceptually different possible types of multiverses. And they are not mutually exclusive: more than one type of multiverse can be at work simultaneously.
It’s a truly great work of popular science, IMO, and I enthusiastically recommend it for anyone asking these kinds of questions.
It’s used as a gimmick in three SF books I’ve read - Brin’s “Earth,” Baxter’s “Manifold:Time” and MacLeod’s “Learning the World”
The existence of an infinite number of universes is not inconsistent with the models you describe. And that’s about all we can say. We don’t know anything about other universes, and probably don’t have any way of knowing.
If there are multiple universes existing within one higher-dimensional something-verse, must those individual universes necessarily be disjoint? What prevents separate universes from intersecting one another?
Distance, in some versions of cosmology. In other versions nothing does, and it’s entirely possible for one universe to intersect another.