What is the size of a singularity in a black hole?

[PAllen]

PAllen, I am not interested in the event horizon. My question is can the collapse to a true singularity be stopped at the quark level or some other form of matter level in the same way that a lower mass stops at the neutron star level. I am just trying to find a way out of an infinite density true singularity.

Not a chance with current physical theories. With some successor theory to SM+GR, I presume yes, but there is no way (I know of) to guess what the nature of this maximally collapsed state is. A string theorist might say it is a cat's toy (ball of string ).

Meanwhile, the quark star has actually been proposed as model of something that forms instead of an event horizon.

 

[PAllen]

You are saying that all event horizons always have to mean there is a mathematical singularity inside. Do you have the proof for this? I presume that this means the maths has failed and we have yet to find out what real world Physics is preventing the true singularity?

These are called the singularity theorems. Yes, it is presumed that they imply that GR breaks down somewhere inside the event horizon. I have said this 3 times already - new physics is the only answer. But nobody knows what applies instead. Picking a random object that is part of known theories *outside* event horizon and guessing - does this stop the collapse inside? - is meaningless. I might as well say that if pink frosted donuts form, the collapse stops.

 

[Chalnoth]

PAllen, I am not interested in the event horizon.

One of the interesting things is that it may be possible to describe everything about a black hole by only describing the event horizon.

My question is can the collapse to a true singularity be stopped at the quark level or some other form of matter level in the same way that a lower mass stops at the neutron star level. I am just trying to find a way out of an infinite density true singularity.

You need a new theory of gravity for this. General Relativity won't allow it.

You are saying that all event horizons always have to mean there is a mathematical singularity inside. Do you have the proof for this? I presume that this means the maths has failed and we have yet to find out what real world Physics is preventing the true singularity?

Yes, it is a proven theorem in General Relativity that if you have an event horizon, there is a singularity inside it. See here:
http://en.wikipedia.org/wiki/Penrose–Hawking_singularity_theorems

 

[Chronos]

It seems safe to say we do not grasp the physics at work inside the BH event horizon. Infinite density creates paradoxes that probably cannot be resolved without a working [and testable] theory of quantum gravity.

 

[Chalnoth]

Infinite density creates paradoxes that probably cannot be resolved without a working [and testable] theory of quantum gravity.

Those paradoxes can only be resolved by making the density not actually infinite.

 

[stevebd1]

I just wanted to explain my question again:

Most Physicsts agree that there is likely no true singularity and that what is required is a theory of quantum gravity to explain what is going on. Some say that the singularity inside a black hole is of the order of the Planck length ie. one notch above a true singularity. I am asking if there are intermediate states of collapse to prevent matter collapsing to this state?

If heavy enough a massive star can collapse to a neutron star.
A heavier star might collapse to some other denser stable form of matter eg. a quark star.
A still heavier star might collapse to some other denser form of matter which is still larger than the Planck length.
A still heavier star might collapse to a black hole whose singularity is the Planck length above.
A super massive black hole has collapsed to a Planck length singularity, but the mass and thus density is higher than the previous case.

This is the question I am asking.

There is something called a black star which considers the idea of degenerate spacetime-

http://en.wikipedia.org/wiki/Black_star_(semiclassical_gravity )

 

[Tanelorn]

It seems safe to say we do not grasp the physics at work inside the BH event horizon. Infinite density creates paradoxes that probably cannot be resolved without a working [and testable] theory of quantum gravity.

I don't understand what a theory of quantum gravity would look like. I thought that what would be required is an understanding of the physics of the next, and then the next, most compressed forms of matter after a neutron star? This degeneracy link seems relevant:

http://en.wikipedia.org/wiki/Degeneracy_pressure

Also Preons and Preon stars!
http://en.wikipedia.org/wiki/Preon
http://en.wikipedia.org/wiki/Preon_star#Preon_stars

 

[Chalnoth]

I don't understand what a theory of quantum gravity would like.

I think that the expectation is that due to no hair theorems of black holes, the properties of the matter that falls into the black hole are likely to be pretty much irrelevant. It is gravity and gravity alone that is likely to be relevant in describing the structure of a black hole.

If you want more understanding, you should see about learning something about what string theory and loop quantum gravity have to say about black holes. Those are our two candidate quantum gravity theories, after all. Personally, I have almost no knowledge about what either says, so I can't be of much help.

 

[PAllen]

I don't understand what a theory of quantum gravity would look like. I thought that would be required is an understanding of the physics of the next, and then the next, most compressed forms of matter after a neutron star? This degeneracy link seems relevant:

http://en.wikipedia.org/wiki/Degeneracy_pressure

To add to what Chalnoth said, as long as GR is held true, the theory of matter you apply inside the horizon is truly irrelevant. The singularity is approached not so much in space as in time - moving forward in time is equivalent to collapse to the singularity. The world line of any particle has nowhere to move in time except towards the singularity. Any theory *of* matter is embedded in the spacetime which has this fundamental causal structure. You can view it as an inverse of the big bang.

No one believes this is really what happens. What it shows is that the solution *must* involve a new theory of gravity, not just a better model of degenerate matter. Such a new theory of gravity is presumed to result from encompassing gravity plus the standard model phenomenology in some coherent framework. All the approaches I know of would involve sidestepping the GR catastrophe in part by saying spacetime itself is what needs radical modification in the black hole regime.

 

[YoungDreamer]

Could a black hole be just like a star in that it is like a factory for creating elements, however in a black hole the gravity is so great that it is creating forms of matter that are currently undetected? Or perhaps even creating matter into a parallel universe?

I know that's a little more science fiction than science I'm just wondering if that could be an actual possibility.

 

[Chalnoth]

Could a black hole be just like a star in that it is like a factory for creating elements, however in a black hole the gravity is so great that it is creating forms of matter that are currently undetected? Or perhaps even creating matter into a parallel universe?

I know that's a little more science fiction than science I'm just wondering if that could be an actual possibility.

I don't think so. Basically, the interior of the black hole is expected to be far too violent for any matter to survive at all.

 

[PAllen]

Could a black hole be just like a star in that it is like a factory for creating elements, however in a black hole the gravity is so great that it is creating forms of matter that are currently undetected? Or perhaps even creating matter into a parallel universe?

I know that's a little more science fiction than science I'm just wondering if that could be an actual possibility.

Mostly no, but the details depend on the theory assumed.

1) Classical GR: Singularity, all mass in zero volume. Nothing gets out, ever (event horizon).

2) Semi-classical GR: All mass eventually ( 10^70 years or more) gets out of the black hole, but only as quasi-thermal Hawking radiation (mostly photons; smaller amounts of other particles; looks thermal, but isn't really). Semi-classical treatment can's say what the state of matter inside the horizon is.

3) Not yet known theoretical model: Who knows? Most likely, similar to (2) except there is a plausible description of superdense matter, and of what happens to (or replaces) spacetime as we know it in such an extreme region.

 

[daveian]

Thanks for responses on the size of a singularity which poses a further question on the size of the universe at time zero (Big Bang); infinitely small or not? I read that GR can not handle the calculations when the universe was youger than Planck time. One can still speculate however.

 

[Chalnoth]

Thanks for responses on the size of a singularity which poses a further question on the size of the universe at time zero (Big Bang); infinitely small or not?

Not. That would be a singularity, and a singularity is nonsensical. Anything nonsensical cannot exist in reality.

 

[beatljuice]

Size of Kerr-Newman Ring Singularity?

I'm looking for the relative size (circumference?) of a ring singularity in a Kerr-Newman (rotating) black hole.

I'm assuming it is 2 dimensional - not having any volume. Or, is it still a 1 dimensional singularity traveling in a circle? Or, 2 point singularities orbiting each other?

Is it related to the mass, or velocity, or both?

 

[stevebd1]

I'm looking for the relative size (circumference?) of a ring singularity in a Kerr-Newman (rotating) black hole.

I'm assuming it is 2 dimensional - not having any volume. Or, is it still a 1 dimensional singularity traveling in a circle? Or, 2 point singularities orbiting each other?

Is it related to the mass, or velocity, or both?

Though it only applies to Kerr BH (i.e. spin only), you might the following thread (and some of the links included) of use-

https://www.physicsforums.com/showthread.php?t=540360

 

[graybass]

These are called the singularity theorems. Yes, it is presumed that they imply that GR breaks down somewhere inside the event horizon. I have said this 3 times already - new physics is the only answer. But nobody knows what applies instead. Picking a random object that is part of known theories *outside* event horizon and guessing - does this stop the collapse inside? - is meaningless. I might as well say that if pink frosted donuts form, the collapse stops.

Awesome!