Singularity in reference to blackholes and right before the big bang?

[fa7alerr0r]

Now correct me if I'm wrong. Gravitational singularity is when It has a defined mass but no volume and the equation for density is d=m/v. If a black hole's mass is say 10^40 yottagrams
and its a singularity so it has no volume = 0. How can it have infinite density if the equation is (10^40 yottagrams)/0 wouldn't that be undefined density?

 

[marcus]

I don't think astrophysicists claim that singularities exist in nature.
A singularity is a breakdown in some manmade theory.
Or you could say it is the place where the manmade theory breaks down.

There have been singularities in various other fields of science. they usually got rid of them by fixing the theory so it doesn't blow up or fail at that point.

In astronomy the kind of singularity you hear about is this infinite density, infinite curvature business (trouble with the theory around BB and BH). I don't think anybody believes such blowups actually occur. The problem is, what improved theory do we use instead so we don't get a singularity---and what really happens.

there was an international workshop on this last year, various experts presented their ideas.
Google "Kitp singularities"
(it was a 2-week conference at KITP, an institute at Univ. Santa Barbara)
If you can't get the videos of the talks, let me know and I will help.

 

[Arch2008]

Well there is emerging theory that singularities don’t have to exist, as well as the Loop Quantum Gravity work. However, some might caution that they need to show some of that proof thing.
In the mean time, Roy Kerr used General Relativity to prove that the mass of a spinning star collapses into a ring with the width of the Planck length and zero height. The zero height part gives the ring zero volume as well (volume equals length times width times height). Zero volume causes the density to approach infinity. http://en.wikipedia.org/wiki/Ring_singularity

GR has passed every test so far, unlike some other stuff.

 

[fa7alerr0r]

ty guys

 

[George Jones]

In the mean time, Roy Kerr used General Relativity to prove that the mass of a spinning star collapses into a ring with the width of the Planck length and zero height. The zero height part gives the ring zero volume as well (volume equals length times width times height). Zero volume causes the density to approach infinity. http://en.wikipedia.org/wiki/Ring_singularity

GR has passed every test so far, unlike some other stuff.

And Penrose, and then Penrose and Hawking, showed that GR predicts singularities under much more general conditions.

 

[Jonathan Scott]

And Penrose, and then Penrose and Hawking, showed that GR predicts singularities under much more general conditions.

I think that's subject to the additional assumption (which I don't think should be counted as part of GR itself) that Hilbert's physical interpretation of the radial coordinate in the vacuum solution is correct and Schwarzschild's is not.

 

[George Jones]

I think that's subject to the additional assumption (which I don't think should be counted as part of GR itself) that Hilbert's physical interpretation of the radial coordinate in the vacuum solution is correct and Schwarzschild's is not.

These theorems don't assume particular solutions.

 

[Jonathan Scott]

These theorems don't assume particular solutions.

I think that those theorems are roughly equivalent to "if there's an event horizon somewhere, there must be a singularity too". It is the question of whether event horizons occur in reality which depends on the assumption about the radial coordinate.