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Offline rwjefferson

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Is a black hole infinitely dense?
« on: 14/11/2010 23:05:30 »
Is black hole mass infinitely dense?
Is this proved or dogma?

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rwjefferson

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Offline Bill S

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Is a black hole infinitely dense?
« Reply #1 on: 15/11/2010 00:31:13 »
I look forward to an answer to this question, because my own belief is that it is not possible to measure infinite density (or infinite anything), so any such claim could be only theoretical.   
 

Offline JP

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Is a black hole infinitely dense?
« Reply #2 on: 15/11/2010 01:49:01 »
I don't think anyone can definitively answer this question since our theories don't cover it, and we certainly can't look inside a black hole to see the answer.  I think most people would guess that a black hole isn't infinitely dense, because infinities tend not to actually exist in nature (although we use them as good approximations to a lot of things when working out mathematical models).
 

Offline QuantumClue

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Is a black hole infinitely dense?
« Reply #3 on: 15/11/2010 09:03:16 »
It isn't proven as such. Penrose and Hawking singularities dictate that a black hole has a singular region which is infinitely dense. Infinitely dense in the sense matter is crushed to a certain point inside the black hole. By all practical means, it seems correct since information cannot escape from our universe.
 

Offline syhprum

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Is a black hole infinitely dense?
« Reply #4 on: 15/11/2010 19:33:29 »
The density of the smallest common black holes formed by the collapse of a star is quite easy to calculate, assuming the mass to be 1.989*10^30 *1.4 Kg= 2.785*10^30 Kg and the diameter  (re Hawking) to be 8.272 Km the density works out at
1.3 *(1,392,000/8.272)^3=tons/M^3=6.1948*10^15 tons per cubic meter.
This of course the density of the blackhole as defined by the event horizon, the density of the so called central singularity is a matter for conjecture.
« Last Edit: 16/11/2010 15:30:28 by syhprum »
 

Offline Soul Surfer

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Is a black hole infinitely dense?
« Reply #5 on: 16/11/2010 11:38:54 »
It is true that smaller black holes are very dense indeed but Infinity is a purely mathematical term and only applicable to mathematical and not physical matters.  the ultimate or peak density of a collapsing black hole will be higher than the density needed to collapse it in the first place but I am sure it will NOT be infinite.  The truth is, we don't know and cannot observe what happens but we know very well a lot of physical things that could allow us to model it. 

The simplest model could be based on a non rotating Swartzchild black hole and Hawking radiation.  As the black hole collapses the event horizon of which we are familiar prevents radiation from coming out to free space but it does not prevent radiation from escaping for a short distance before falling back into the hole.  Each layer of this event horizon can radiate hawking radiation even though it will eventually fall back but this takes time and saps the energy of the hole as the matter continues to collapse towards a singular point this radiation gets more and more intense and continues to sap the hole until it reaches an equilibrium point.  It is possible to calculate the size of this point (although I have not done it yet) but is most definitely not infinitely small and is probably larger than a Planck unit so this does not require quantum gravity.  Just saying the collapse is to a mathematical singularity is really a copout used by early workers in the field before Hawking radiation was conceived that has been copied by most of the popular writers in the field.

Its about time this fallacy was put to bed by someone with authority.  Because it causes endless questions like this and prevents people from turning their thoughts to more useful matters.

It is interesting to note that like white dwarf stars and neutron stars the more massive the hole is the smaller the final collapse will be because of the greater energy that will have to be generated.  This is true even though the first event horizon of the hole becomes larger as the mass of the hole increases. This is a linear function of about one mile for every solar mass inside.
« Last Edit: 16/11/2010 11:44:28 by Soul Surfer »
 

Offline Pikaia

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Is a black hole infinitely dense?
« Reply #6 on: 16/11/2010 11:59:49 »
Infinity is a sign that there is something wrong with the theory - the physics needs refining. In order to know what happens in a black hole we need a theory of quantum gravity, which we do not have at present, but it is likely that at very small scales something happens to prevent us getting to infinity.
 

Offline Soul Surfer

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Is a black hole infinitely dense?
« Reply #7 on: 16/11/2010 12:23:50 »
Piakia  I agree that a theory of quantum gravity would be very helpful that is what everyone says but I do not believe that it is essential for any progress to be made. A great deal of work has been done for many years on the topic of string theory and quantum gravity and is still going on. This has produced a vast number of potential mathematical models with no link with reality and no way of selecting which one may be correct.  I strongly believe that we have not used enough modelling based on what we DO know to help direct us to solutions of this problem.  Notably the detailed modelling using standard classical and quantum theories of the processes of collapse inside the event horizon of a rotating black hole right up to the limit where our theories fail.  I strongly believe that the devil is in the detail.

We know that the Kerr black hole collapses to a "ring" singularity.  The equations have been solved.  This is just the same as saying we know that Our universe will eventually die through the thermodynamic heat death.  This does not mean that interesting things do not happen on the way, like us observing our universe!
 

Offline syhprum

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Is a black hole infinitely dense?
« Reply #8 on: 16/11/2010 17:36:04 »
There is ample evidence that stellar mass and super large blackholes exist but is there any evidence that small ones exist ?, the universe is not old enough or cool enough for stellar mass ones to have lost any of their mass so the only way small ones could exist is if they were created at the time of the 'bigbang'.
Have any been detected ?.   
 

Offline Bill S

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Is a black hole infinitely dense?
« Reply #9 on: 16/11/2010 18:05:45 »
Quote from: SS
Infinity is a purely mathematical term and only applicable to mathematical and not physical matters.
Wow!!! Someone with (possibly infinitely) more knowledge of the subject than I, has actually said what I have frequently been castigated for saying, in another forum.       I'm going to celebrate. Thanks, Soul Surfer.  ;D 
 

Offline QuantumClue

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Is a black hole infinitely dense?
« Reply #10 on: 16/11/2010 18:30:55 »
Quote from: SS
Infinity is a purely mathematical term and only applicable to mathematical and not physical matters.
Wow!!! Someone with (possibly infinitely) more knowledge of the subject than I, has actually said what I have frequently been castigated for saying, in another forum.       I'm going to celebrate. Thanks, Soul Surfer.  ;D 

Well, it's a matter of opinion, or even choice of what kind of infinities we are dealing with. It isn't necesserily a true statement. For instance, infinities pop up in theory all the time. A good example is an infinite spacetime void. This is actually acceptable, and in every sense of the theory, is a physical infinity as well.
 

Offline Bill S

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Is a black hole infinitely dense?
« Reply #11 on: 16/11/2010 20:33:08 »
Quote from: QuantumClue
infinities pop up in theory all the time. A good example is an infinite spacetime void. This is actually acceptable, and in every sense of the theory, is a physical infinity as well.
For "infinite spacetime void" substitute "boundless spacetime void", it fits the theory just as well, but could involve a completely different physical reality.
 

Offline Soul Surfer

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Is a black hole infinitely dense?
« Reply #12 on: 17/11/2010 18:00:34 »
A truly mathematically infinite universe requires there to be an infinite number of identical earths in which every person is doing the exact same thing as we are doing at this moment and an greater infinity of worlds like the earth where people are doing slightly different things and that is before we come to a range of other options like rearranging the stars.

This to my mind is completely stupid and that is why I much prefer the concept of unbounded or indefinite for the physical concept.
 

Offline Bill S

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Is a black hole infinitely dense?
« Reply #13 on: 17/11/2010 20:36:48 »
Quote from: SS
I much prefer the concept of unbounded or indefinite for the physical concept.
So do I !!!

I’m not expert enough where mathematical infinities are concerned too be able to make any profound comments about what any of the more complex forms might be like, but for a true physical infinity, I think you have not gone far enough.  If you apply Cantor's "infinity of infinities" to the Universe you would, as you say, have infinite numbers of everything, and everything that happens, happening an infinite number of times.  However, this would be just a mathematical infinity.  A mathematical ‘reality’ means only logical self-consistency and this does not require physical existence to validate it.

One often meets statements like: “In infinity everything that can happen will happen, an infinite number of times.”  This statement contains at least two elements that are at variance with the concept of physical infinity: “…will happen”, because there can be no past or future in infinity; and “…number of times”, because there can be no numbers, or differentiated times in infinity.  I said “at least two” because, strictly, “happen” has no place in infinity because it implies action, and action involves change.

How, then, can we re-word the original statement so as to bring it into line with the concept of physical infinity?  It would have to be something like: “Every thing that can be, is”.   
 

Offline Pikaia

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Is a black hole infinitely dense?
« Reply #14 on: 18/11/2010 16:30:36 »
A truly mathematically infinite universe requires there to be an infinite number of identical earths in which every person is doing the exact same thing as we are doing at this moment and an greater infinity of worlds like the earth where people are doing slightly different things and that is before we come to a range of other options like rearranging the stars.

This to my mind is completely stupid and that is why I much prefer the concept of unbounded or indefinite for the physical concept.
Mind-boggling, yes, but not stupid; it is an inevitable consequence of an infinite universe. I find it far more plausible and easy to understand than a finite universe, with the weird geometry that it implies.
 

Offline peppercorn

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Is a black hole infinitely dense?
« Reply #15 on: 18/11/2010 17:30:52 »
Mind-boggling, yes, but not stupid; it is an inevitable consequence of an infinite universe. I find it far more plausible and easy to understand than a finite universe, with the weird geometry that it implies.

But an infinite (unbounded) universe has infinities in it! That's not at all a comfortable concept IMO.  'weird' geometry is walk in the park in comparison!
 

Offline Bill S

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Is a black hole infinitely dense?
« Reply #16 on: 18/11/2010 22:59:12 »
Quot homines tot sententiae; but as long as you discuss mathematical infinities as though they were synonymous with physical infinity you are likely to keep going round in circles.
 

Offline imatfaal

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Is a black hole infinitely dense?
« Reply #17 on: 19/11/2010 11:04:49 »
Quot homines tot sententiae; but as long as you discuss mathematical infinities as though they were synonymous with physical infinity you are likely to keep going round in circles.

Or at least go round in a circle that after an infinite amount of time will bring you back to your starting place
 

Offline JP

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Is a black hole infinitely dense?
« Reply #18 on: 19/11/2010 11:25:35 »
A truly mathematically infinite universe requires there to be an infinite number of identical earths in which every person is doing the exact same thing as we are doing at this moment and an greater infinity of worlds like the earth where people are doing slightly different things and that is before we come to a range of other options like rearranging the stars.

This to my mind is completely stupid and that is why I much prefer the concept of unbounded or indefinite for the physical concept.

I find this far less weird than lots of things in quantum mechanics, which does appear to be real, so I don't think it's stupid at all.

The one thing I think everyone can agree on about whether infinity can be physically realized is that no one has proof one way or the other, just opinions.
 

Offline Bill S

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Is a black hole infinitely dense?
« Reply #19 on: 20/11/2010 22:06:04 »
Quote from: JP
The one thing I think everyone can agree on about whether infinity can be physically realized is that no one has proof one way or the other, just opinions.

Absolutely true (at least in my opinion) ;D

The more I think about infinity, though, the more I find it difficult to escape various "opinions"; two of which are:
1. Nothing that is finite can become infinite.
2. Accepting a physical infinity is preferable to being stuck with infinite regression.
 

Offline CPT ArkAngel

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Is a black hole infinitely dense?
« Reply #20 on: 21/11/2010 02:26:51 »
I like the way you say it Bill  [:o)], but your first assumption is quite a revelation!!!
 

Offline Bill S

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Is a black hole infinitely dense?
« Reply #21 on: 21/11/2010 13:39:42 »
Quote
your first assumption is quite a revelation!!!

This means that either I have it wrong, or you need to do some more thinking. :-\ 

Give me an example of something finite that becomes infinite, we can work from there.
 

Offline CPT ArkAngel

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Is a black hole infinitely dense?
« Reply #22 on: 21/11/2010 16:40:04 »
I mean this assumption is right: nothing finite can become infinite.
 

Offline Bill S

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Is a black hole infinitely dense?
« Reply #23 on: 23/11/2010 17:21:51 »
Quote from: ArkAngel
nothing finite can become infinite

Great! Someone who is willing to put this in writing. Would you also agree about the next step: "Anything that is infinite must also be eternal"?
 

Offline CPT ArkAngel

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Is a black hole infinitely dense?
« Reply #24 on: 24/11/2010 02:38:59 »
it sounds very logical to me, but some people might disagree about the properties of time...

And what about something eternal, does it have to be infinite?
 

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Is a black hole infinitely dense?
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