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Suppose in the end there will remain only one very large black hole, others have died. Now this black hole had absorbed all the matter and energy of the universe due to conservation principle. Everything just cannot disappear. It has to be conserved somewhere. So this last black hole is a very massive thing.

And finally it must die too because the dark energy is pulling it apart. So it will not die like others. It is a special last black hole that is killed specially by the dark energy. It does not just evaporate. It is killed by dark energy (don't get too caught up on the killing idea, just make something up to make sense because this question is not really about it).

So when the last black hole dies it generates so much energy and bursts all the mass stored in its core that it starts another big bang. So another universe starts in the last black hole of this universe. But this new universe will never be able to escape out of the black hole because nothing escapes the event horizon.

Now i know this last part seems completely wrong. The last black hole already died so there is no event horizon left. But suppose through some mechanism the event horizon persists because this last black hole did not die like the other black holes simply evaporating. It was killed by dark energy, torn apart so maybe its event horizon still remains intact.

Then that means one universe is formed in another and we can never really communicate with the other universes.

Is this at all possible?

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    $\begingroup$ The universe isn't going to end up as a single massive black hole so your question isn't really answerable. $\endgroup$ – John Rennie Jun 6 at 6:25
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    $\begingroup$ You are essentially describing an Oppenheimer-Snyder white hole (a time reversed black hole). This white hole looks like an expanding universe inside an event horizon, which nothing can cross from outside. $\endgroup$ – safesphere Jun 6 at 6:48
  • $\begingroup$ @JohnRennie Is that true? I thought a consequence of accelerating expansion was that eventually galaxies outside of the Local Group would be redshifted to undetectability, so that observers in the very far future might become unable to reconstruct the history that we've worked out. (I am not confident that I can find the article where I read this.) And since we have now observed that gravitational orbits are, eventually, unstable against gravitational radiation, having only black holes remaining is a plausible long-term state. The time scales are really, really long, though. $\endgroup$ – rob Jun 6 at 12:51
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Dark energy doesn't pull apart black holes unless we have $w<-1$ and get a Big Rip scenario. If you have an empty universe with dark energy and a black hole there is the de Sitter-Schwarzschild class of solutions to general relativity that describe it, and this is a static situation.

There are other considerations, as mentioned in the comments. The universe is too big and expands too fast to let all matter coalesce into a single black hole. Basically, we have a horizon (right now) of about 4.9 Gpc beyond which matter cannot reach no matter how much it is accelerated, so if it all started imploding together right now we would just get super-big black holes about 9.8 Gpc apart - but realistically we end up with one big black hole per gravitationally bound cluster of galaxies.

Even if you had everything in a big black hole it is generally believed it will just evaporate due to Hawking radiation in the long run, leaving a thin soup of mostly photons and neutrinos behind.

Some arguments have suggested black hole singularities actually turn into baby universes, but this is a different argument and would, if it happened, produce multiple new universes rather than a new aeon.

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  • $\begingroup$ "we have a horizon (right now) of about 4.9 Gpc" - There is no experimental evidence that such a horizon actually exists. $\endgroup$ – safesphere Jun 7 at 5:50
  • $\begingroup$ Sure, but the horizon is part of the lambdaCDM consensus model. $\endgroup$ – Anders Sandberg Jun 18 at 7:35
  • $\begingroup$ For a long time the flat Earth resting on a giant tortoise was the consensus model and people were burned alive for contradicting. What any model says is not the absolute truth, so adding something like, "According to Lambda-CDM", may provide more clarity. $\endgroup$ – safesphere Jun 18 at 8:00

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