I have four questions about black holes and universe formations.
Do new universes form on the other side of black holes?
Was our own universe formed by this process?
Was our big bang a black hole seen from the other side?
Are there solid reasons why this might not be the case?
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!).
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.
No, because universes aren't created in this way, ours wasn't, either.
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).
Yes, see above.
The definition of the universe is that which that contains all the exists. Therefore by that simple definition, there cannot be "another" universe under any circumstance. Could a black hole in some way be a gateway to a different plane of spacial and temporal dimensions in a multi-verse? Probably not, depending on the global topology of the universe and whether or not a multiverse can actually exist, but it doesn't make physical sense that the mass of a star would somehow all of a sudden become a gate-way to another realm if you think about it that way. All a black hole is, is an object such that spacial and temporal metrics approach 0 as you approach it's boundary, and there's no reason to think that has anything to do with other realms of existence. It doesn't have to be any sort of mystical thing either, there are equations to track the trajectories of projectile particles down to the singularity with certain assumptions that a black hole isn't anything special and that space still exists inside it according to relativistic distortion, for large black holes space is so distorted it would take days and days to reach the singularity to an observer falling down it.
If you want an honest answer, the answer is WE DO NOT KNOW. It could be, it could be not.
Look, just couple of weeks or months ago we find out that our Earth's core is significantly different than we previously thought.
We don't know how many ground water is on our planet. It may be surprising but we really don't know that. Here is more about the fact that we actually don't know how much ground water we have in lot of areas on our planet, more here from Jay Famiglietti from the University of California, Irvine (he speaks about that at about 43:45) http://youtu.be/F4DCS4uZOUk?t=43m45s
If we don't know these things that are macroscopic and relatively easy to observe and find out, then you have to admit that our knowledge about black holes, what is inside of black holes (we are not 100% sure what is inside of our own planet as I mentioned earlier; this information changes every few years or decades accourding to the new research and tests) and the origin of the Universe and Universes is in its infancy and we have a lot of research ahead. We are only in the beginning.
So, all we have right now is the observation of the effects of this "things" called black holes and a lot of mathematical formulas that could or could not be true.
So, in my opinion it's a good question, but unfortunately nobody can give a definitive answer, if he is honest, of course.
