SWaB: how dense is a black hole?

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notFritzArgelander
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SWaB: how dense is a black hole?

#1

Post by notFritzArgelander »


He uses the "S" word as if singularities were real! Naughty! Naughty! ;)

But, then, there follows a nice discussion about how more massive black holes are less dense.

https://www.forbes.com/sites/startswith ... 93c26b5b92
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Re: SWaB: how dense is a black hole?

#2

Post by Kanadalainen »


Thanks not_Fritz, very nice article, despite the wanton usage.
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Re: SWaB: how dense is a black hole?

#3

Post by notFritzArgelander »


I know I'm a fuss about the usage of the "s" word. It's an interesting case of bewitchment by language....
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Re: SWaB: how dense is a black hole?

#4

Post by Gmetric »


The logic for Ethan’s use of the “S” word is illustrated in this article.

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Re: SWaB: how dense is a black hole?

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Post by notFritzArgelander »


Gmetric wrote: Mon Oct 14, 2019 2:42 am The logic for Ethan’s use of the “S” word is illustrated in this article.

Yes, yes. I cheerfully concede that General Relativity implies singularities and gleefully riposte "So what?" That logic (GR implies singularities) does not justify the usage of singularities as if they are real physical entities and not mere artifacts of the underlying mathematics.

The reasons why singularities should not be treated as real include:

1) They are always hidden unobservable behind an event horizon and so are therefore in principle unobservable.
2) They are an extrapolation from the physics we know (GR, QM and QFT) to domains where they are no longer valid. Before a singularity is realized one has to pass through the Planck scale of energy, mass, length, and/or time. https://en.wikipedia.org/wiki/Planck_units As we approach that scale we know less about what the physics is. So before a singularity is reached the physics we know breaks down and projecting a singularity is not justifiable. Without a quantum gravity that incorporates GR this extrapolation is unjustifiable.
3) A singularity in GR is a point of infinite spacetime curvature. That alone tells you that the physics must be wrong.
4) There is an alternative theory of gravity which agrees with General Relativity on all testable length scales due to Einstein Cartan Sciama and Kibble. This theory has novel features as the Planck scale is approached. The spins of particles are coupled to a torsion tensor which provides a repulsive force. In this theory there is no singularity even without a quantum gravity.

My bottom line is that when your physical theory predicts an infinity, it is wrong or incomplete. It breaks. So speaking of a singularity as if it were a real physical entity is an error. When your theory gives an infinity, it's broken.

Previously, the ultraviolet catastrophe pointed out the shortcomings of classical radiation theory and pointed the way to quantum physics.
https://en.wikipedia.org/wiki/Ultraviolet_catastrophe It is ironic that Einstein got his Nobel for overcoming the singularity in classical radiation theory with quantum considerations.

It is widely expected by folks working in quantum gravity from both the string theory and covariant loop quantum gravity POVs that a successful quantum gravity that replaces GR will be singularity free.

From https://phys.org/news/2018-12-black-hol ... arity.html we have some quotes that provide an example that Ethan's view of singularities as real is a mistake.
"For example, general relativity predicts that there are places in the universe where gravity becomes infinite and space-time simply ends. We refer to these places as 'singularities.' But even Einstein agreed that this limitation of general relativity results from the fact that it ignores quantum mechanics."
Interestingly, even though loop quantum gravity continues to work where general relativity breaks down—black hole singularities, the Big Bang—its predictions match those of general relativity quite precisely under less extreme circumstances away from the singularity. "It is highly non-trivial to achieve both," said Singh, associate professor of physics at Louisiana State. "Indeed, a number of investigators have explored the quantum nature of the black hole singularity over the past decade, but either the singularity prevailed or the mechanisms that resolved it unleashed unnatural effects. Our new work is free of all such limitations."
So I will continue to remind with good humored teasing that Ethan's realist treatment of singularities cannot and will not be allowed to stand unchallenged. Thanks for the opportunity to repeat in detail the rationale for calling out Ethan's error.
Last edited by notFritzArgelander on Mon Oct 14, 2019 3:36 am, edited 1 time in total.
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Re: SWaB: how dense is a black hole?

#6

Post by AntennaGuy »


:lol: RE: "ovarian loop quantum gravity"... Heh. I think you meant "covariant" ? Unless, perhaps, this is a "more feminist" theory of GR?
Interesting stuff, nFA. Keep it coming.
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Re: SWaB: how dense is a black hole?

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Post by notFritzArgelander »


AntennaGuy wrote: Mon Oct 14, 2019 3:35 am :lol: RE: "ovarian loop quantum gravity"... Heh. I think you meant "covariant" ? Unless, perhaps, this is a "more feminist" theory of GR?
Interesting stuff, nFA. Keep it coming.
Durned auto correct got me again. :lol: Fortunately I was able to still edit and correct the typo. Thanks!
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Re: SWaB: how dense is a black hole?

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Post by Gmetric »


notFritzArgelander wrote: Mon Oct 14, 2019 3:21 am
Gmetric wrote: Mon Oct 14, 2019 2:42 am The logic for Ethan’s use of the “S” word is illustrated in this article.

Yes, yes. I cheerfully concede that General Relativity implies singularities and gleefully riposte "So what?" That logic (GR implies singularities) does not justify the usage of singularities as if they are real physical entities and not mere artifacts of the underlying mathematics.

The reasons why singularities should not be treated as real include:

1) They are always hidden unobservable behind an event horizon and so are therefore in principle unobservable.
2) They are an extrapolation from the physics we know (GR, QM and QFT) to domains where they are no longer valid. Before a singularity is realized one has to pass through the Planck scale of energy, mass, length, and/or time. https://en.wikipedia.org/wiki/Planck_units As we approach that scale we know less about what the physics is. So before a singularity is reached the physics we know breaks down and projecting a singularity is not justifiable. Without a quantum gravity that incorporates GR this extrapolation is unjustifiable.
3) A singularity in GR is a point of infinite spacetime curvature. That alone tells you that the physics must be wrong.
4) There is an alternative theory of gravity which agrees with General Relativity on all testable length scales due to Einstein Cartan Sciama and Kibble. This theory has novel features as the Planck scale is approached. The spins of particles are coupled to a torsion tensor which provides a repulsive force. In this theory there is no singularity even without a quantum gravity.

My bottom line is that when your physical theory predicts an infinity, it is wrong or incomplete. It breaks. So speaking of a singularity as if it were a real physical entity is an error. When your theory gives an infinity, it's broken.

Previously, the ultraviolet catastrophe pointed out the shortcomings of classical radiation theory and pointed the way to quantum physics.
https://en.wikipedia.org/wiki/Ultraviolet_catastrophe It is ironic that Einstein got his Nobel for overcoming the singularity in classical radiation theory with quantum considerations.

It is widely expected by folks working in quantum gravity from both the string theory and covariant loop quantum gravity POVs that a successful quantum gravity that replaces GR will be singularity free.

From https://phys.org/news/2018-12-black-hol ... arity.html we have some quotes that provide an example that Ethan's view of singularities as real is a mistake.
"For example, general relativity predicts that there are places in the universe where gravity becomes infinite and space-time simply ends. We refer to these places as 'singularities.' But even Einstein agreed that this limitation of general relativity results from the fact that it ignores quantum mechanics."
Interestingly, even though loop quantum gravity continues to work where general relativity breaks down—black hole singularities, the Big Bang—its predictions match those of general relativity quite precisely under less extreme circumstances away from the singularity. "It is highly non-trivial to achieve both," said Singh, associate professor of physics at Louisiana State. "Indeed, a number of investigators have explored the quantum nature of the black hole singularity over the past decade, but either the singularity prevailed or the mechanisms that resolved it unleashed unnatural effects. Our new work is free of all such limitations."
So I will continue to remind with good humored teasing that Ethan's realist treatment of singularities cannot and will not be allowed to stand unchallenged. Thanks for the opportunity to repeat in detail the rationale for calling out Ethan's error.
Thank you for calling it out and for this detailed and thorough response. I was gonna pop-up a link in which loop quantum gravity basically provided a lovely counter argument. :) but, I think you seem to have covered most, if not all of the bases. Once again, thanks for the response and additional reading material.
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Telescopes: Sky-Watcher ED72II, Sky-Watcher PDS130, Sky-Explorer SN F4 200mm astrograph and Vixen F11.1 90mm
Cameras: Nikon D5300 modded, Canon Kiss X8i modded, Cooled Canon kiss X4 modded, Atik 16IC and 383 colour, ASI120MC, QHY5LII
Mount: Sky-Explorer HEQ 5 belt driven
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