[GrandMasterK]

I was just wondering this. It's hard for me to imagine a point infinitely small that has position in space. can someone please explain to me how that works? And is the accepted notion that the center of a black hole is a hole in the universe? (which in my mind means that the matter is being stored outside of the unvierse). Or is does all of it's matter still exist in space in our universe just condensed down to a ridiculously small area? Or is it one in the same?

Thanks.

[DrRocket]

GrandMasterK, on 8 October 2011 - 11:15 PM, said:

I was just wondering this. It's hard for me to imagine a point infinitely small that has position in space. can someone please explain to me how that works? And is the accepted notion that the center of a black hole is a hole in the universe? (which in my mind means that the matter is being stored outside of the unvierse). Or is does all of it's matter still exist in space in our universe just condensed down to a ridiculously small area? Or is it one in the same?

Thanks.

General relativity predicts that the interior of a black hole is singular. That is a bit different than "black holes have singularities". The difference is subtle and technical -- a singularity in GR is a failure of spacetime to be timelike geodesically complete.

It is generally believed that the singularity indicates a breakdown of the general theory of relativity that may in the future be understood via a theory of quantum gravity, but no one knows for sure. This is consistent with the belief (also unproved) that the singularity is not physical.

[Realitycheck]

Think about how an electron's orbital diameter is about 1.06*10^-10m, or an angstrom, across and the size of a proton is about 1*10^-15m across. Now collapse the two into each other to where there's no space in between any of the particles and this thing which was the size of a star is now about 12 miles across. That's a black hole. It's not an infinitely dense point.

[granpa]

bear in mind that black holes are defined by their event horizons rather than by singularities.

[Mystery111]

DrRocket, on 9 October 2011 - 12:08 AM, said:

General relativity predicts that the interior of a black hole is singular. That is a bit different than "black holes have singularities". The difference is subtle and technical -- a singularity in GR is a failure of spacetime to be timelike geodesically complete.

It is generally believed that the singularity indicates a breakdown of the general theory of relativity that may in the future be understood via a theory of quantum gravity, but no one knows for sure. This is consistent with the belief (also unproved) that the singularity is not physical.

I don't. I think a singularity is breakdown of our understanding, rather than the physical theory.

I like singularities. I don't see why infinities should always be frowned upon.

[granpa]

how you view a singularity depends a lot on whether you view space and time as discrete or continuous.

[Mystery111]

Forget technical terms. Most of the times, scientists dispute the existence of these exotic regions simply because we cannot fathom them.

I sware this is true. No one in the scientific community, apart from a few, actually can appreciate regions of spacetime which have singular applications. No one likes infinities, never mind the vacuum!

Also, rocket said

a singularity in GR is a failure of spacetime to be timelike geodesically complete.


...is a statement itself wrapped up in some rather complicated physics. To understand the swap between spacelike and timelike conditions rely on an understanding of the mathematics behind black holes themselves, which I would wager, not many here can appreciate.

ps.... in fact if you are really nice to me, I Might even take you through the maths of black holes leading to where space time flip

[DrRocket]

granpa, on 9 October 2011 - 02:01 AM, said:

how you view a singularity depends a lot on whether you view space and time as discrete or continuous.

ALL currently accepted models treat spacetime as a manifold (continuous). Attempts have been made to formulate discrete models, but so far none have panned out.

The singularity theorems cited in most cases are based on general relativity. Einstein-Cartan theory results in different singularity theorems or no singularities at all, but no current experiment can distinguish between Einstein-Cartan theory and general relativity. Both treat spacetime as a manifold.

In short, you are all wet.

[A Tripolation]

Mystery111, on 9 October 2011 - 01:59 AM, said:

I don't. I think a singularity is breakdown of our understanding, rather than the physical theory.

It's of the theory. GR is not refined enough to handle the appearance of a singularity. As DrRocket said, the theory falls apart.

[Mystery111]

A Tripolation, on 9 October 2011 - 05:23 AM, said:

It's of the theory. GR is not refined enough to handle the appearance of a singularity. As DrRocket said, the theory falls apart.

Except this is used as a reason that it cannot be physical, at least this is the general consensus. Just because relativity - or our application of relativity cannot handle them, should and I refine the arguement again, should not indicate a breakdown of physical theory. Our general understanding of relativity will break down, but there most certainly will be a theory which will deal with it, and if I am right, will help pave a more physical understanding of singular regions of spacetime.

[IM Egdall]

Realitycheck, on 9 October 2011 - 12:19 AM, said:

Think about how an electron's orbital diameter is about 1.06*10^-10m, or an angstrom, across and the size of a proton is about 1*10^-15m across. Now collapse the two into each other to where there's no space in between any of the particles and this thing which was the size of a star is now about 12 miles across. That's a black hole. It's not an infinitely dense point.

Are you saying the event horizon is about 12 miles in diameter?

And if there is no space between the particles at the black hole center, then isn't the center infinitely dense?

[baric]

I don't think anyone knows exactly what happens to matter due to the intense pressure at the center of a stellar core massive enough to overcome neutron degeneracy pressure.

One thing we do know is that the escape velocity at the surface of such a collapsed core exceeds the speed of light. It seems more plausible that quantum forces come into play rather than simply assume that the core shrinks to a zero-volume point with an infinite density.

[Realitycheck]

Basically, if the event horizon is larger than the object's surface, then it is considered a black hole. I believe that in the case of supermassive black holes at galactic cores, the event horizons are substantially larger than the singularities underneath them. This is what sets it apart from a neutron star, which doesn't have as much gravity to have that effect.

If black holes (stellar) were infinitely dense, then the singularities would contract to a diameter infitely smaller than 12 miles, which defies logic, if you ask me. This is kind of a subject of debate right now, since most older theory considers a singularity to be an infinitely dense point, such as all of those neutrons and electrons compacted into a point much smaller than the sum of the diameters of all the particles, whereas Hawking has kind of broken from the pack and reclassified the black hole singularity as being finitely dense, essentially the sum that I just described. I believe this makes much more sense than the standard larger-than-life mythology of black holes of old.

[IM Egdall]

Realitycheck, on 10 October 2011 - 08:46 AM, said:

Basically, if the event horizon is larger than the object's surface, then it is considered a black hole. I believe that in the case of supermassive black holes at galactic cores, the event horizons are substantially larger than the singularities underneath them. This is what sets it apart from a neutron star, which doesn't have as much gravity to have that effect.

If black holes (stellar) were infinitely dense, then the singularities would contract to a diameter infitely smaller than 12 miles, which defies logic, if you ask me. This is kind of a subject of debate right now, since most older theory considers a singularity to be an infinitely dense point, such as all of those neutrons and electrons compacted into a point much smaller than the sum of the diameters of all the particles, whereas Hawking has kind of broken from the pack and reclassified the black hole singularity as being finitely dense, essentially the sum that I just described. I believe this makes much more sense than the standard larger-than-life mythology of black holes of old.

Good stuff here. Thanks. But again what does the 12 miles refer to and how is it calculated?

[granpa]

http://www.google.co...tron+star+miles

[Realitycheck]

Well, this is second-hand information for me, but 12 miles would be the diameter of the singularity, or mass of neutrons and electrons fused together. And, in my mind, this would only pertain to stellar black holes. Somebody said that supermassive black holes would have about the same size singularities, which doesn't really make sense considering all of the extra mass, so I'm not really sure about that part of the theory. A neutron star wouldn't be contracted as much and would be about 15 miles across.
A good way to double check it would be take all of the material in a collapsed star, collapse all of the protons into electrons, creating neutrons, add that to preexisting neutrons and leftover electrons, fuse them all together and calculate its diameter.

[baric]

Realitycheck, on 10 October 2011 - 02:24 PM, said:

Well, this is second-hand information for me, but 12 miles would be the diameter of the singularity, or mass of neutrons and electrons fused together. And, in my mind, this would only pertain to stellar black holes. Somebody said that supermassive black holes would have about the same size singularities, which doesn't really make sense considering all of the extra mass, so I'm not really sure about that part of the theory. A neutron star wouldn't be contracted as much and would be about 15 miles across.
A good way to double check it would be take all of the material in a collapsed star, collapse all of the protons into electrons, creating neutrons, add that to preexisting neutrons and leftover electrons, fuse them all together and calculate its diameter.

This article (http://io9.com/56775...ile+wide-sphere) talks about a 1.9 solar mass neutron star with a diameter of 12 miles.

However, the core of a black hole (the "singularity") would be much, much smaller since the neutrons would have collapsed to at least their constituent quarks.

This post has been edited by baric: 10 October 2011 - 03:43 PM