Where does matter in a black hole go?

Andrew Pontzen was on hand to answer Paul's cosmic question...

Andrew - Yes, absolutely. Black holes do suck in matter; anything that's unlucky enough to fall into the grips of a black hole is never seen again. And, honestly, we don't quite know the answer because black holes are still very mysterious things. If you take Einstein's theory of general relativity, which we were discussing a bit earlier on, the best theory of gravity we have. If you take that totally at face value, what happens to that stuff after it falls in is it keeps falling down, and down, and down, into a central point where it literally gets crushed into a single point. A mathematical point or a singularity.

However, that doesn't really make sense. We don't really believe that you can crush something that had originally had some extent and some normal piece of matter down to literally a single point. And what we think is really going on at some point, at quantum mechanics, which is the theory of how very small things work, has to come into play. Now as we were mentioning earlier on in this programme, we do have some ideas about how to combine quantum mechanics and general relativity, and it leads to predictions like Hawking radiation that very slowly actually mass finds it way out of a black hole but we don't really understand the details. When we try and drill down and understand how does the stuff that fell in find it's way out of a black hole, could you trace an individual bit of stuff into a black hole and then out. It's much more murky.

Chris - Giles.

Giles - You know you say it's unlikely a singularity exists as one might imagine it, then what actually happened. Maybe this is too big a question, before the Big Bang. I mean just before the big bang happened wasn't everything sat in one spot somewhere?

Andrew - Well again, the honest answer is we don't know. There's a lot of we don't knows in cosmology, although there are a lot of ideas. And one of the prevailing ideas at the moment is that the Big Bang as well, in the way that we think of it as everything sor of exploding out from a point, which again, is a prediction that's coming from Einstein's theory of general relativity. We now think that probably never really happened. Something very much like it happened but it wasn't quite that picture of everything was a point. We have ideas like inflation, which replace that idea with something very different.

Chris - George Osborne had something to say about that...

Andrew - Yeah, yeah. We always seem to be borrowing names from other things in real life which doesn't help. But inflation is an idea about the very early universe. The first tiny fraction of a second of the universe's existence and it replace the idea of an actual singularity of things exploding out from a point with a process that we can actually understand and make calculations about. In much the same way that we now think a black hole doesn't really have an infinitely dense point at it's centre.