# Black Holes

1. Jul 13, 2008

### math_04

This may strike some people as really weird but after reading the book, God and the New Physics by Paul Davies, I came across a paragraph where he explains what happens at the singularity of a black hole. At the singularity, there is no concept of time apparently. So it is impossible to leave a black hole otherwise you would leave before you went in. This is what Paul Davies discussed. Everything is infinite and basically, you would be at time=0, in other words the point where the universe has just begun. For me, this seems like concrete proof of baby universes forming.

Black holes are formed from the gravitational collapse within a star after it has burned out all its nuclear energy. So all that mass collapses and all that mass squeezed down creates incredible gravitational forces. The gravity is so strong that it tears apart space time. This is all from what I have read here and there.

So at that point of singularity, a baby universe forms but obviously is closed away from us due to the laws of physics (infinite density, at time= 0 etc etc). This has probably been mentioned many times but I dont know why it has not been accepted. Any reasons why?

2. Jul 13, 2008

### mathman

The description of what happens inside a black hole is based on the assumption that general relativity is exact, while quantum theory has no role. The problem with this is that quantum theory is here and trying to reconcile it with G.R. inside a black hole can't be done. The reality is that no one knows what really happens inside a black hole.

3. Jul 13, 2008

### yuiop

Basically, once you have a singularity, you can make up any physics you like, such as white holes, new universes, time travel, etc, etc. I have spent a lot of time in this forum and the Relativity forum trying to explain why singularities do not form, but it feels like telling a bunch of kids that Santa Claus does not exist.

4. Aug 2, 2008

### Almanzo

From the point of view of an observer who will forever remain outside the black hole, anything which falls in will take an infinite time to reach the horizon, and will therefore never reach the singularity (which is beyond the horizon).

That said, there might not be an observer who is capable of remaining forever outside the black hole. If the universe is going to recollapse into a big crunch, one could say that all black holes will eventually coalesce, and everything will, at some time in its history, pass inside. In that case everything reaches the singularity in finite time, and the singularity is simply the end of time; the last moment of the universe.

On the other hand, the universe may be undergoing accelerated expansion. It might be so that a black hole can never properly form, because everything which seemed destined to cross the horizon will actually reappear at some future date, being drawn back by the expansion of space. This would imply that no horizon existed at any stage at all. Or this might be true for some apparent black holes, but not all of them, depending on the details of the accelerated expansion. There might then be apparent black holes, without an actual singularity, and real black holes, with a singularity which cannot be reached (from the point of view of an outside observer) in finite time.