This is where the concepts of eternal inflation, the multiverse, and the existence of many disconnected Universes come from.

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Artistic impression of a Multiverse — where our Universe is only one of many. These Universes will be disconnected from one another, have slightly different, variable density and structure within them, and will have their Big Bangs begin at different times. They will never collide or interact, and will instead expand away from one another as they're embedded in a background of inflating space.

If you accept that inflation is a stage that occurred in the Universe's past prior to the hot Big Bang, and that the Universe itself is inherently quantum in nature, the existence of a multiverse is unavoidable. Even though we cannot observe these other Universes, we can observe a huge amount of evidence for inflation, indirectly pointing to its inevitability. We can also observe a huge amount of evidence that the Universe itself is quantum, even though we have no proof that inflation itself behaves as a quantum field. If you put these pieces together, it unambiguously leads to the prediction that our Universe should be only one of countlessly many Universes, all embedded in an eternally inflating, expanding background. One Universe is not enough. Even though we cannot detect it, the prediction of a multiverse is unavoidable.