On 8/17/2013 10:58 AM, Dan Asimov wrote:
You're asking me?
But seriously: Don't black holes lead to a singularity of the usual physics equations? I suppose the event horizon occurs before this singularity is reached.
Right. The event horizon contains the singularity. For a large BH, as at the center of the galaxy it is many years from the event horizon to the singularity (and that's the way to put it because once you're inside the event horizon the singularity isn't in a different place from you, it's in your future at the same place, i.e. you don't "move to it" rather "it happens to you".
But I imagine no one knows what happens when the singularity is reached -- is that the case?
Right, although no one really believes there's a singularity, only that general relativity no longer applies. And most physicists hope/believe that when the relation between quantum mechanics and gravity is understood it will explain how the singularity is just an approximation.
If so, are there widely believed hypotheses about what happens? E.g., maybe at that point a black hole behaves like a star in reverse time? Or (woo-woo) gives rise to a disjoint piece of the universe?
Lee Smolin has theorized that the "singularity" gives rise to another universe - but I don't think he's been able to work out anything convincing absent the hoped for quantum theory of gravity. The more pressing question seems to be whether information is conserved (as quantum mechanics implies) when stuff falls into a BH and then the BH evaporates (per Hawking radiation). Whether you chose "yes" or "no" some accepted principle of physics gets violated. Brent