The fact is we don't have an answer for that. The multiverse theory is hard to prove right or wrong simply because those other universes are outside our Universe. So we cannot prove their existence by calculating the mass that exists in the Universe where we live. There is also the possibility that those other universes are invisible to us. So we might just guess about the existence of the universes outside our Universe. There is a couple of versions of the multiverse theories. The first one is the original multiverse theory where other universes are outside the Universe as we know it. But another more exotic version is the matryoshka universe theory. In that theory, the black holes are involving another universe. The idea is that the information cannot vanish. The black hole doesn't destroy information. Black holes store information. And that information that is stored in black holes can take the form of the Universe. There is the possibility that there ar...