What does the singularity at the bottom of a black hole consist of other than quantum foam?

Answer 1

Hi stephen b

There's an important point to make here: the singularity at the centre of black holes is *not* physical. The name comes from the mathematical behaviour of the description of the black hole.

Briefly:
General relativity is represented symbolically in this way:

Shape of space-time = distribution of mass energy

To make the equations describing a simple black hole, you locate all of your mass centrally and then solve the general equations to come up with something called a "metric". The metric describes space-time paths around the hole. The simplest black hole solution (an uncharged, non-spinning black hole) is called the Schwarzschild metric. When you plug a radius of zero (r=0) into the schwarzschild metric you end up with "divide by zero" errors - as you know division by zero is undefined. When this happens physicists and mathematicians say that the metric has "become singular", and the singularity happens when r=0.


So... the central singularity is a mathematical result, a divide by zero error. Some people refer to this by the grand sounding phrase "all the laws of physics break down at the singularity", and in a manner of speaking that's true. What it actually means is that the theory which provided the metric, general relativity, can't tell us what is actually happening at r=0. So we might be interested to ask, "well what happens when r gets close to zero?"

General relativity (GR) tells us that "implosion is compulsory". For the schwarzschild metric all paths inside the event horizon lead inexorably to the centre. No mass can stay between the horizon and the centre. GR can describe that internal space almost all the way to the centre, it is limited only in that it is a classical theory - it can't address quantum scales. So once we get close enough to the centre that quantum interactions matter GR can't help us anymore. We need a quantum theory of gravity to guide us from here and possibly to resolve the central singularity into some physical realism as well, but as yet we don't have such a theory. Speculations can be made on what it looks like within quantum scale distance of the centre by making so-called "semi-classical" educated guesses, and this is where you've heard of a roiling quantum foam. One of the ways that extreme gravitational curvature is manifest is through energy - more curvature (ie stronger gravitational gradient) means more energy available in the field. And the quantum vacuum uses available energy densities to create particle pairs, so the roiling quantum foam is a reasonable educated guess. What will be interesting to discover is what happens when we reach the scale where length and time might be quantised (the Planck scale), and if we can work out what the physical properties masked by the singularity actually are.


Hope this helps!
The Chicken

Answer 2

No one has gone into a black hole and returned alive to tell us, so we don't know.

"At the singularity, though, the laws of physics, including General Relativity, break down. Enter the strange world of quantum gravity. In this bizzare realm in which space and time are broken apart, cause and effect cannot be unraveled. Even today, there is no satisfactory theory for what happens at and beyond the singularity. "

Answer 3

http://www.arxiv.org/abs/gr-qc/0504029 & http://www.physicsforums.com/showthread.php?p=761933

Its called the Black Hole Bounce.

States that its possible the singularity is just another entrance to another part of our Universe. "In this paper they come closer to saying that spacetime might re-expand from the pit of a black hole, forming another tract to the universe by another bang." Maybe like a Quasar or White Hole?

If you have any ideas what are at the bottom, I'd love to hear!

Thanks!

Answer 4

I don't know and I don't want to find out firsthand.