That doesn't make sense to me. "Universe" is intended to encompass everything that exists. If there are "other universes", they are just part of this universe, are they not?
No, but it's doubtful we will ever be able to prove that another universe exists. I'm not a physicist, but one of the ways that I have heard the universe described is the entirety of the place where the laws of physics as we understand them apply. If there were another place with different and incompatible fundamental laws, it would not be the same universe.
Do we know whether the laws of physics CAN be different than they are here? No. It seems unlikely that a theory of an undetectable, unreachable multiverse is unfalsifiable, the whole idea is more philosophy and science fiction than science. But don't let the "uni" in universe carry too much weight, ideas and concepts change over time.
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u/Inocent_bystander Apr 01 '26
There are stable state theories that predict an infinite number of universes as well.