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Size of a Singularity 
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#19
Jul511, 03:39 PM

P: 721

Pallen, arent all Black Holes pseudo singularities? Therefore their density goes up as their mass increases, and all of which are the most dense forms of matter possible?



#20
Jul511, 04:10 PM

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PF Gold
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What happens inside an event horizon is another matter altogether. For one thing, it is unobservable, in principle, under current theory. GR, as a literal, classical theory says there must be some form of singularity inside, but it is most likely a very chaotic one, not one of the neat exact solutions of GR (still within the realm of classical GR  the exact solutions are unstable  any slight deviation magnifies inside the horizon). [I ignore the possibility if naked singularities; they are not currently predicted by plausible models within our universe, so far as I know]. What really happens inside the horizon? I know of no physicist who thinks classical GR will continue to hold. So far as I know, no candidate models make meaningful predictions. Inside an event horizon, a quark star provides no additional insight without a working theory of this regime. Whether a quark star is a possible evolutionary state of some stellar process that, in a few circumstances, avoids an event horizon is an interesting problem in stellar dynamics, but irrelevant as a model of black holes. 


#21
Jul511, 05:56 PM

P: 12

What is the difference between a black hole singularity and the Big Bang singularity?
How does one distinguish one singularity from another? Do they have any properties at all? If we picture the universe as a ball, and a black hole singularity as having infinite gravity can we picture it as a gravity well to the center of the ball; to the Big Bang itself? If there is no Hawking Radiation (it has never been proved, right?) is it possible that black holes feed the Big Bang itself? Since time does not exist under infinite gravity there is no before and after between the two singularities, and since a singularity does not exist within the geometry of the universe, aren't all singularities thus the same singularity existing in the "same place"? 


#22
Jul511, 06:53 PM

P: 721

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. 


#23
Jul511, 07:12 PM

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#24
Jul511, 07:16 PM

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PF Gold
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If you want to say that the mathematical singularity in a black hole is not to be taken seriously as representing something physical, then I have the impression that the majority of physicists would probably take your side of the bet if a sixpack was at stake. Since blackhole singularities in GR are hidden behind event horizons, we will of course never get a chance to check by any direct observation whether they are really singular or not. The singularity that we do get to observe is the big bang singularity. 


#25
Jul511, 07:32 PM

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PF Gold
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Hi, Octavianus,
Welcome to PF! 


#26
Jul511, 07:52 PM

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PF Gold
P: 5,059

Neutron stars are presumed to exist, and are not black holes. Quark stars, if they existed, would not be black holes. Both of these are alternatives to the formation of event horizons  the collapse stops before the event horizon forms. Meanwhile, an event horizon can form with a sufficiently large assembly of matter with quite low density (e.g. for a black hole with the mass of our galaxy, the density when the event horizon was crossed would only be that of water). Further, once an event horizon is formed, GR predicts that no matter what form matter takes, nothing can stop the formation of a zero volume singularity inside. Quark stars or neutron stars would be of no 'help' at all inside the event horizon. The only thing that would relevant here is new physics. 


#27
Jul511, 08:01 PM

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Now, because the Planck length is so incredibly short, we don't necessarily expect to see any evidence of quantum gravity any time soon. We might have to get within a few orders of magnitude of the Planck length to see such evidence, and right now we're around 16 orders of magnitude away. 


#28
Jul511, 08:21 PM

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#29
Jul511, 08:35 PM

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#30
Jul511, 10:15 PM

P: 721

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.
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? 


#31
Jul511, 10:33 PM

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


#32
Jul511, 10:39 PM

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#33
Jul611, 12:18 AM

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http://en.wikipedia.org/wiki/Penrose...arity_theorems 


#34
Jul611, 12:49 AM

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PF Gold
P: 9,432

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.



#35
Jul611, 01:23 AM

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#36
Jul611, 01:51 AM

P: 608

http://en.wikipedia.org/wiki/Black_s...ssical_gravity) 


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