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I have four questions about black holes and universe formations.

  1. Do new universes form on the other side of black holes?

  2. Was our own universe formed by this process?

  3. Was our big bang a black hole seen from the other side?

  4. Are there solid reasons why this might not be the case?

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3 Answers

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It's not exactly a duplicate, but have a look at my answer to Entering a black hole, jumping into another universe---with questions.

For certain types of black holes it's possible to find a trajectory that takes you inside the event horizon then back out again, but when you emerge you'll find there is no way (without travelling faster than light) to get back to where you started.

The question is whether this counts as another universe (I would say not) or indeed whether the trajectory is physically realistic or not (Luboš would say not and I don't know enough about the subject to comment!).

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  1. No, physically, no new Universes ever get formed. In particular, the extended Penrose causal diagrams with new infinite regions just show the maximal extension of the spacetime that is possible mathematically, ignoring physical processes inside the black hole. In physics and reality, the extension is unphysical because the naive extrapolation by Einstein's equations can't be trusted deeper than the inner (Cauchy) horizon of a black hole (because Cauchy horizons are unstable) and/or singularity, so the solution doesn't continue, and it's enough to "kill" the new infinite space. There has also been a different question whether an inflating universe may be created in the bubble where the inflaton jumps to a higher level, here the answer isn't conclusive.

  2. No, because universes aren't created in this way, ours wasn't, either.

  3. No, a black hole can't be the same thing as the Big Bang. The Big Bang singularity is an initial spacelike singularity which would be similar to the white hole. But even the white hole is wrong because it cannot exist. The whole situation around the white hole is forbidden - the entropy would decrease with time but after the Big Bang, the entropy was increasing (like always in allowed situations, because of the second law).

  4. Yes, see above.

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Aside from the existence of the initial low-entropy state, the entropy of the big bang certainly increases over time just like all other physical properties and it obeys the laws of GR. What separates this from the process argued for a new universe with the creation of a BH? I'm just confused, it seems like the argument against a "white hole" is specific to a certain conception that's not the same as a second big bang. – AlanSE Dec 4 '12 at 13:06
I would like to take your word for it, but i think that any definitive validation of your statement goes by first clarifying this question: physics.stackexchange.com/q/45817/955 – lurscher Dec 4 '12 at 16:01
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This statement (black holes are wormholes to growing universes) follows from Einstein-Cartan theory, which attempts to incorporate spin into Einstein's geometric theory of gravitation.

Note that this theory has its own problems when coupling to the EM field due to its inherent asymmetric energy-momentum tensor following from the spin tensor contribution.

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Please clarify. Why does this arise from E-C theory? What problems does it cause? Please answer the question (if you didn't notice, Do new universes form on the other side of black holes? Was our own universe formed by this process? Was our big bang (the one that happened in our universe about 13.7 billion years ago) a black hole seen from the other side? Are there solid reasons why this might not be the case?) – namehere Dec 4 '12 at 10:03
@namehere: I am not google, nor a GR expert. The fact that a theory admits such an interpretation is not at all proof of the concept, so I cannot give a yes or no. The problems it causes are somewhat explained here: ift.unesp.br/users/jpereira/views/view1.pdf – rubenvb Dec 4 '12 at 10:07
At least mention your reference in your post. The reference does not provide any concrete calculations or justifications for its conclusion. And presumably E-C theory is not the only theory that predicts this effect. Lastly, if you don't want to answer the question don't answer it (use the comment for this purpose. You're rep. is well above the required limit). – namehere Dec 4 '12 at 10:15
I did not quote any specific reference because as far as I can tell, every other paper says something different, which leads me to conclude the whole isn't finished quite enough to answer this question with a strict yes or no. Heck, if you look at it like that, in its current form, the question is unanswerable, in part because no-one has observed anything to prove things one way or another. – rubenvb Dec 4 '12 at 10:22
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If you believe your reference is correct, then why not quote it? Now onto you saying the question is unanswerable, do you think you have enough knowledge on this matter? Do you think nobody else has adequate knowledge on this matter? Who are you to judge these matters if your inability to answer is because of your lack of knowledge? – namehere Dec 4 '12 at 11:16
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