Black Hole - Questions

[JAL]

Firstly I am only a layman as the advanced maths goes so am only able to talk in laymans terms but am interested in any problems.
Last night I watched a programme about black holes hosted by apparently very clever people but it left many questions unanswered mainly about the singularity not conforming with any laws of physics as we understand them, as apparenly the answers to the maths is infinity.
Is it possible that the gravitational pull within a black hole can condense matter to the point where it has no atomic structure i.e. all the parts of an atom are fused together then fused with surrounding atoms finally making up essentially a single huge particle, and acting as such, forming the singularity at the center. This would then form the nucleus of the galaxy with all the stars etc forming the rest of the structure. (Could this lead to universes within universes theory).
Also if black holes are as dense as people seem to think then surely at some point fusion must take place releasing vast ammounts of energy which must be going somewhere - dark matter?
It must be possible to work out how densely matter can be condensed then comparing that with the size and weight of a black hole. The one at the center of our galaxy is apparently the equvalent of 4 million suns but of course you would need to know its physical size.
Has anyone tried doing the maths with a black hole a a sigle particle rather than a mass of small ones?
Maybe this is all rubish, I just look for potential answers and leave more knowlegeable people to decide.

[rrrADAM]

To many, there is no difference between the singularity at the heart of a black hole and the singularity that the universe 'banged' from.

Lee Smolin even goes further with this idea:
http://en.wikipedia.org/wiki/Fecund_...cund_universes
For more on that, read his book, The Life of the Cosmos

[Frink]

Wiki/Black hole.

[GodofRock13]

The problem with the mechanics of the "inside" of a black hole is the presence of the singularity. This is a singular point (ie 1 d) lying in a 3 (possibly more) dimensional world. The equations that Einstein gave us essentially break down. Hawking helped us overcome this with a change of coordinates, yet something was still lacking.

Einstein showed us that gravity can be thought of us a geometry of spacetime. A star would be analogous to a bowling ball on a tightly held piece of saran wrap. The singularity would have poked a hole in the wrap and the curvature would become infinite.

Another problem is the presence of the event horizon. The final line where even light cannot escape. It hides behind this horizon. So no observations can be made. There are things called naked singularities which do not have this event horizon to hide behind, but nature abhors them so we have yet to find them.

hope this helps

[editor]

There doesn't have to be a singularity in a black hole.
A super massive black hole can have the density of air.
See Wikipedia. http://en.wikipedia.org/wiki/Supermassive_black_hole

Also, JAL, your statement "Is it possible that the gravitational pull within a black hole can condense matter to the point where it has no atomic structure i.e. all the parts of an atom are fused together " is a reality in a neutron star. This is still one stage above a Black Hole.

You are thinking of a Black Hole as being a collapsed star. This is only one type.
My definition of a BH is a volume of space from which light can not escape.

[Frink]

Does anyone actually teach ''nature abhors naked singularities?''

[RobertR]

JAL

We don't have to get as exotic as black holes to get things to "blow up".

Newton's equation is . F = GMm/r squared.

GMM is a number, and so make r very very small. F then gets very large.

When r = zero, F = infinity. Anything divided by zero is infinity.

If F is infinity then since F stands for force, we have an infinity large force to deal with.

An infinitly large force is going to accelerate what ever gets near it to an infinite speed, (since were talking about gravity).

These things are impossible. Thus the physics breaks down, that is it does not describe reality. i.e blows up.

The way out is to theorize that something on this very small scale occures that is different from extending what we observe on a larger scale to be the case. Such as when we get this small the number of dimensions increases, thus instead of getting increasingly smaller, things spread out again into other dimensions.

This way we never get to being as small as zero.

It is at this stage only a way out, as it has not been demonstrated to be the case.

[GodofRock13]

Originally Posted by editor

There doesn't have to be a singularity in a black hole.
A super massive black hole can have the density of air.
See Wikipedia. http://en.wikipedia.org/wiki/Supermassive_black_hole

I was giving the black hole definition as a collapsed star. There are quantum singularities that exist for fractions of a second. Those follow a completely different set of rules and probably not what the question was looking for.

All black holes have a singularity. Supermassive ones are just big enough that one might survive a while before hitting gravity that kills. It is difficult to describe a black hole in terms of density since we don't know what goes on inside. In a kerr BH you might never hit the singularity because it ossicaltes around the "origin" of the black hole (this is where Star Trek the movie went with it)

Theres a pretty good undergrad book written by Taylor and Wheeler that requires little calculus, that is where i started because I didnt know a black hole from an apple at the time.

[JAL]

Many thanks for the replies. The question of how far matter can be compressed seems to have been answered by editor and the neutron star. The question about the release of energy seems to have been overlooked. Following the same principle that powers the sun presumably given enough pressure fusion would take place untill the maximum atomic weight is reached releasing energy untill the process stops, or would fission take place after a certain point? If light can't escape then can this energy, if not where does it go or is it held by the gravitational forces and just building up over time. I am just pondering about what could lie within the event horizon.

[GodofRock13]

Originally Posted by Frink

Does anyone actually teach ''nature abhors naked singularities?''

I might have seen it in Lee Smolin's book or Brian Greene's, but as a grad student working in high energy, more over wanting to get my PhD in quantum black holes and singularities I truly believe that they are as elusive as the magnet monopole (see Dirac's paper- would explain why quantum is how it is).

That quote I made doesn't mean they exist, the universe as we know it just doesn't like to have them. Much like a BH has an event horizon, so does our universe. There is the point where you 'could' ride the edge of expanion much like surfing a wave (ignore how) where they could live beyond this. But we just cannot know for sure. Theory is awesome and fun but it has match our observational evidence (this alone could be a giant topic thread).

Robert R gave the mathematical reason why we can't do much physics inside the event horizon 1/0=not a defined answer.

JAL- Hawking and Penrose have done much work on the quantum mechanics at (not beyond) the event horizon and have found that a black hole does slowly evaporate. However for a black hole to evaporate, it would take almost 10x the age of the current universe (when i said slow i meant slllllllllloooooooooooooooowwwwwwwwwwwwwwwwwwwwwww ww)
I hate quoting wikipedia because the page author could misrepresent something from the text book, etc. But here is the page
http://en.wikipedia.org/wiki/Black_hole_evaporation

[RobertR]

Much like a BH has an event horizon, so does our universe.

I assume you are talking about cosmological event horizion?

If you identify the event horizion here on earth, and then travel to it, it would no longer be one. It would become your proper space, just a normal as the space your in now.

They are due to space expansion, which increases the greater the distance from you.

Our effective universe ends at that horizion.

Maybe I didn't understand what you were saying?

[Farsight]

Originally Posted by JAL

Last night I watched a programme about black holes hosted by apparently very clever people but it left many questions unanswered mainly about the singularity not conforming with any laws of physics as we understand them, as apparenly the answers to the maths is infinity.

The program adhered to the Misner/Thorne/Wheeler interpretation of a black hole, and didn't mention the Weinberg interpretation which is true to the original relativity. It omitted the infinite time dilation at the black hole event horizon. When you look at what Einstein actually said, what you read is that gravitational time dilation is the result of a reduced speed of light at that location as compared to some other location. You can't measure the reduced c locally, because it applies to matter too, also reducing your clock rate. The result of this is that the waterfall analogy would only be correct if the water fell slower and slower until it reached the event horizon, where it stopped and effectively turned to ice. This prevents the formation of a singularity in the real world. This is the Oppenheimer "frozen star" description of a black hole, which is akin to a gravastar. It's more of a black hole than the traditional black hole, since the event horizon becomes a surface around a hole in spacetime.

Originally Posted by JAL

Is it possible that the gravitational pull within a black hole can condense matter to the point where it has no atomic structure i.e. all the parts of an atom are fused together then fused with surrounding atoms finally making up essentially a single huge particle, and acting as such, forming the singularity at the center.

Yes and no. The pressure can squeeze all the structure out of matter to make what is essentially a single huge particle, and since c=0 the normal measures of time and space and everything else no longer apply. But it's then wrong to think of this as something of zero size.

Originally Posted by JAL

This would then form the nucleus of the galaxy with all the stars etc forming the rest of the structure.

There's certainly something interesting about the relationship between supermassive black holes and the surrounding galaxy.

Originally Posted by JAL

(Could this lead to universes within universes theory).

No, because of the c=0. That means nothing is happening, and never ever will.

Originally Posted by JAL

Also if black holes are as dense as people seem to think then surely at some point fusion must take place releasing vast ammounts of energy which must be going somewhere - dark matter?

The energy can't get out, it's trapped. Dark matter is just inhomogenous space, but that's one for another day.

Originally Posted by JAL

It must be possible to work out how densely matter can be condensed then comparing that with the size and weight of a black hole. The one at the center of our galaxy is apparently the equvalent of 4 million suns but of course you would need to know its physical size.

Ever attended a New Year's eve party and done the hokey cokey? The more people who join the circle, the bigger it gets. But measuring its external size and its mass doesn't tell you the density of the people inside the circle.

Originally Posted by JAL

Has anyone tried doing the maths with a black hole as a sigle particle rather than a mass of small ones?

Yes, I think so. I'll see if I can find something for you if anybody else hasn't.

Originally Posted by JAL

Maybe this is all rubbish, I just look for potential answers and leave more knowlegeable people to decide.

You're right to ask questions. That's what physics is all about. My advice is to do your thinking for yourself.

[editor]

I see no reason why a supermassive BH with low average density and a size measured in lightyears could not have stars and planets on the inside.
Then it just becomes a region of space from which light can not escape.
There's no singularity.
Life goes on as normal, but in a few million years or so gravity will start to reduce the diameter. Unless some force stops the big crunch.
Sound familiar - that's our universe.

[JAL]

Have been doing further reading and decided that singularities in the strictest sense of the word are unlikely to exist within event horizon. Using the term black hole to describe something within an event horizon have discovered the following, that density apears to be more important than mass i.e. black hole can be almost any mass, and largest one found is 18 billion solar masses. I find it very hard to believe that an object of 18 billion solar masses could have formed from a collapsing star within the age of the universe which would point to its origin being at the very beginning or a primordial black hole which would point to the other smbh at galaxy centers being the same and possibly the oldest galaxies forming round them with different shapes forming round different types of BH's.
I also asked myself the question why if a star of 3 solar masses can collapse behind an event horizon why isn't a star of say 20 solar masses already behind one? This brings us to density and spacetime/gravity. Einsteins views of gravity are shown as a flexible sheet (wiki - spacetime) What if that flexible sheet is normal spacetime and objects float on it, their weight or mass is supported if the volume covers a sufficient area, as the volume decreases and mass stays the same it will slowly sink through, could spacetime have a second inflexible oneway layer or floor being the event horizon through which a sufficiently dense object could sink? or am I just talking si-fi. This of course could lead to speculation as to whats under the floor

[PhysBang]

Originally Posted by Farsight

The energy can't get out, it's trapped. Dark matter is just inhomogenous space, but that's one for another day.

What does it mean that. "Dark matter is just inhomogenous space."

Is there mathematics in General Relativity that explains how inhomogeneous spoace can produce the effects of dark matter that are observed and measured?

Is this standard GR mathematics or is this non-standard GR mathematics?

If the first, then what is the problem in those standard papers that derive measurements of dark matter using standard relativity?

If the second, then what is this new mathematics and why should we trust it over the standard, established mathematics?