Formation of singularities

[Willem]

I have a question about the formation of the singularity which supposedly lies at the center of a black hole. A singularity could form for example by the collapse of the core of a massive star after it has depleted its fuel. However, once the core has collapsed down to the Schwarzschild radius, time, from the viewpoint of an observer at a distance, comes to a hold. This is a consequence of the gravitational time dilation which is implied by the general theory of relativity. An event that would last, say, a second for an observer at the Schwarzschild radius, would last an infinite amount of time for a distant observer. Therefore, once the core has collapsed down to the Schwarzschild radius further contraction should, according to the distant observer, take an infinite amount of time. Therefore the singularity can never be formed. What is wrong with this line of reasoning?

[andrew s]

20 minutes ago, Willem said:

Therefore the singularity can never be formed. What is wrong with this line of reasoning?

The problem is that it is only distant observers that do not see it form. If you were an observer inside the Schwarzschild radius you would (according to GR) see it form but that observer could not communicate his observation to the distant observer. Some versions of loop quantum gravity predict that the singularity does not form but bounces back almost immediately. This theory predicts that suitably sized Black Holes formed in the early universe should now be bouncing back and should be observable now (due to the gravitational time dilation). A Nobel prize for any one who spots one.

Regards Andrew