Stephen Hawking Was Wrong - Extremal Black Holes Are Possible (quantamagazine.org) 44
"Even black holes have edge cases," writes Astronomy magazine contributing editor Steve Nadis, in an article in Quanta magazine (republished today by Wired):
Black holes rotate in space. As matter falls into them, they start to spin faster; if that matter has charge, they also become electrically charged. In principle, a black hole can reach a point where it has as much charge or spin as it possibly can, given its mass. Such a black hole is called "extremal" — the extreme of the extremes. These black holes have some bizarre properties. In particular, the so-called surface gravity at the boundary, or event horizon, of such a black hole is zero. "It is a black hole whose surface doesn't attract things anymore," said Carsten Gundlach, a mathematical physicist at the University of Southampton. But if you were to nudge a particle slightly toward the black hole's center, it would be unable to escape.
In 1973, the prominent physicists Stephen Hawking, James Bardeen and Brandon Carter asserted that extremal black holes can't exist in the real world — that there is simply no plausible way that they can form. Nevertheless, for the past 50 years, extremal black holes have served as useful models in theoretical physics. "They have nice symmetries that make it easier to calculate things," said Gaurav Khanna of the University of Rhode Island, and this allows physicists to test theories about the mysterious relationship between quantum mechanics and gravity. Now two mathematicians have proved Hawking and his colleagues wrong. The new work — contained in a pair of recent papers by Christoph Kehle of the Massachusetts Institute of Technology and Ryan Unger of Stanford University and the University of California, Berkeley — demonstrates that there is nothing in our known laws of physics to prevent the formation of an extremal black hole.
Their mathematical proof is "beautiful, technically innovative and physically surprising," said Mihalis Dafermos, a mathematician at Princeton University (and Kehle's and Unger's doctoral adviser). It hints at a potentially richer and more varied universe in which "extremal black holes could be out there astrophysically," he added. That doesn't mean they are. "Just because a mathematical solution exists that has nice properties doesn't necessarily mean that nature will make use of it," Khanna said. "But if we somehow find one, that would really [make] us think about what we are missing." Such a discovery, he noted, has the potential to raise "some pretty radical kinds of questions." Before Kehle and Unger's proof, there was good reason to believe that extremal black holes couldn't exist.
Hawking, Bardeen, and Carter believed there was no way an extremal black hole could form, according to the article, and "in 1986, a physicist named Werner Israel seemed to put the issue to rest."
But the two mathematicians, studying the formation of electrically charged black holes, stumbled into a counterexample — and along the way "also constructed two other solutions to Einstein's equations of general relativity that involved different ways of adding charge to a black hole. Having disproved Bardeen, Carter and Hawking's hypothesis in three different contexts, the work should leave no doubt, Unger said... "This is a beautiful example of math giving back to physics," said Elena Giorgi, a mathematician at Columbia University....
In the meantime, a better understanding of extremal black holes can provide further insights into near-extremal black holes, which are thought to be plentiful in the universe. "Einstein didn't think that black holes could be real [because] they're just too weird," Khanna said. "But now we know the universe is teeming with black holes."
For similar reasons, he added, "we shouldn't give up on extremal black holes. I just don't want to put limits on nature's creativity."
In 1973, the prominent physicists Stephen Hawking, James Bardeen and Brandon Carter asserted that extremal black holes can't exist in the real world — that there is simply no plausible way that they can form. Nevertheless, for the past 50 years, extremal black holes have served as useful models in theoretical physics. "They have nice symmetries that make it easier to calculate things," said Gaurav Khanna of the University of Rhode Island, and this allows physicists to test theories about the mysterious relationship between quantum mechanics and gravity. Now two mathematicians have proved Hawking and his colleagues wrong. The new work — contained in a pair of recent papers by Christoph Kehle of the Massachusetts Institute of Technology and Ryan Unger of Stanford University and the University of California, Berkeley — demonstrates that there is nothing in our known laws of physics to prevent the formation of an extremal black hole.
Their mathematical proof is "beautiful, technically innovative and physically surprising," said Mihalis Dafermos, a mathematician at Princeton University (and Kehle's and Unger's doctoral adviser). It hints at a potentially richer and more varied universe in which "extremal black holes could be out there astrophysically," he added. That doesn't mean they are. "Just because a mathematical solution exists that has nice properties doesn't necessarily mean that nature will make use of it," Khanna said. "But if we somehow find one, that would really [make] us think about what we are missing." Such a discovery, he noted, has the potential to raise "some pretty radical kinds of questions." Before Kehle and Unger's proof, there was good reason to believe that extremal black holes couldn't exist.
Hawking, Bardeen, and Carter believed there was no way an extremal black hole could form, according to the article, and "in 1986, a physicist named Werner Israel seemed to put the issue to rest."
But the two mathematicians, studying the formation of electrically charged black holes, stumbled into a counterexample — and along the way "also constructed two other solutions to Einstein's equations of general relativity that involved different ways of adding charge to a black hole. Having disproved Bardeen, Carter and Hawking's hypothesis in three different contexts, the work should leave no doubt, Unger said... "This is a beautiful example of math giving back to physics," said Elena Giorgi, a mathematician at Columbia University....
In the meantime, a better understanding of extremal black holes can provide further insights into near-extremal black holes, which are thought to be plentiful in the universe. "Einstein didn't think that black holes could be real [because] they're just too weird," Khanna said. "But now we know the universe is teeming with black holes."
For similar reasons, he added, "we shouldn't give up on extremal black holes. I just don't want to put limits on nature's creativity."
So how do you detect one? (Score:2)
If there are no obvious gravitational effects at the event horizon, what is the mechanism for detecting such a thing?
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Re:So how do you detect one? (Score:4, Insightful)
Good question. Of course, if it has a high electric charge that would presumably be detectable and if it was also spinning it would create a magnetic field. The effects on nearby objects should be theoretically detectable.
While this is true for extreme cases, it’s not really possible to have one actually form much of a charge at all. The more charge it has, the more it would repel like and attract the opposite charges quickly neutralizing itself. Further, there aren’t many places you can even find a net charge, there was just an article on slashdot showing the net charge on the earth is about half a volt.
That said, most black holes probably are close to maximally charged with angular momentum because it’s pretty common for material to keep falling in from one direction for a number of reasons. But this maximal amount of counteracting angular momentum is only at the equator, the poles would have zero.
In both cases you would still see the exact same gravitational lensing or nearby body motion (the way we currently detect them), because that has to do with mass and angular momentum and charge don’t factor in.
How to detect wrong scientific conclusions? (Score:2)
The real question is how to detect when a scientific conclusion is wrong, and more importantly, when the wrong scientific conclusion is accepted as fact because of the prestige of the source, institution, or scientific journal.
Like how it was 100% factual by proven science for nearly 200 years that dinosaurs did not have feathers, until a discovery in 2011. https://en.wikipedia.org/wiki/... [wikipedia.org]
Ideas for disussion vs prohibited thoughts (Score:2)
It's bad enough that there is a vocal percentage in any scientific topic on both sides that resorts to a default 'disagree with me and you will be expelled from university and excommunicated from the scientific community' behavior for any 'unapproved nonconformist ideas'.
Politicizing every academic field with excommunication the penalty for anything less than parroting the party line will result in less scientific quality.
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While I agree, institutions are run by people, people have tendencies to accept what they believe and reject what they do not. The real rub is when it comes to funding. There has to be some collection of people who decide on funding. That collection will have its bias and they aren't going to fund something they believe is barking up the wrong tree. Given the number of crackpots out there formulating "theories", how can they not rely on their biases? It is simply the human condition.
If you need examples, ju
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While I agree, institutions are run by people, people have tendencies to accept what they believe and reject what they do not.
The biggest problem is the layperson understanding, scientists using the scientific method are required to disbelieve what there is insufficient evidence for, including areas like math where it can be directly derived but has not yet been done. Only after the evidence exists, is vetted, and reproduced (for various levels of plausible reproduction) can a scientist be confident and thus “believe”. To those not understanding the scientific method of helplessly going where the data says, it looks
Re:How to detect wrong scientific conclusions? (Score:4, Insightful)
There's a big difference between "100% factual by proven science" and simply being rejected for lack of evidence. Feathered dinosaurs were proposed a couple decades after the word "dinosaur" was coined.
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There's a big difference between "100% factual by proven science" and simply being rejected for lack of evidence. Feathered dinosaurs were proposed a couple decades after the word "dinosaur" was coined.
This is spot on.
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Good question. Of course, if it has a high electric charge that would presumably be detectable and if it was also spinning it would create a magnetic field. The effects on nearby objects should be theoretically detectable.
While this is true for extreme cases, it’s not really possible to have one actually form much of a charge at all. The more charge it has, the more it would repel like and attract the opposite charges quickly neutralizing itself. Further, there aren’t many places you can even find a net charge, there was just an article on slashdot showing the net charge on the earth is about half a volt.
You're using the word "not possible" differently from the paper discussed. You're saying it's not likely, because under any "reasonable" scenario it will self-neutralize. They are saying it is not impossible.
...
In both cases you would still see the exact same gravitational lensing or nearby body motion (the way we currently detect them), because that has to do with mass and angular momentum and charge don’t factor in.
Charge is a factor in solution of a Reissner–Nordström black hole, and hence yes, it is a factor in the gravitational lensing. The gravitiational lensing would be peculiar, positive lensing at far impact parameters, and negative lensing at closer distances.
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You're using the word "not possible" differently from the paper discussed. You're saying it's not likely, because under any "reasonable" scenario it will self-neutralize. They are saying it is not impossible.
You ignored the previous beginning sentence
While this is true for extreme cases
Then
Charge is a factor in solution of a Reissner–Nordström black hole, and hence yes, it is a factor in the gravitational lensing.
It’s not a stable and at best an extremely temporary solution [arxiv.org]of maybe 1000 to 100000 years and only when surrounded by a net opposite co-rotating magnetosphere. Not excatly something observed from collapsed magnetars. Otherwise the lifetime would be far less than a year, not really something that exists as a stable object. Further, weak lensing wouldn’t be affected as the net charge is zero in the above case, though for half the mass as electr
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Charge is a factor in solution of a Reissner–Nordström black hole, and hence yes, it is a factor in the gravitational lensing.
It’s not a stable and at best an extremely temporary solution [arxiv.org]
Great link, thanks.
of maybe 1000 to 100000 years and only when surrounded by a net opposite co-rotating magnetosphere. Not excatly something observed from collapsed magnetars.
Again, we're talking different things. The paper we're discussing is about what is possible, where the word "possible" means "not impossible." You seem to be talking about "what will be the result if a real world magnetar collapsed into a black hole, given an assumption that it is immersed in a plasma environment."
The gravitiational lensing would be peculiar, positive lensing at far impact parameters, and negative lensing at closer distances.
No, in the case of a bare Reissner-Nordström black hole the lensing would be quite similar with the same geometry but slightly greater deflection at larger (weak) scale and only the near field strong lensing region would have greatly increased deflection near M=Q.
Nice paper, but they made approximations. Specifically, following equation 24, they assume epsilon is positive. This is true for an uncharged black hole, but I'd like to see it
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Again, we're talking different things. The paper we're discussing is about what is possible, where the word "possible" means "not impossible." You seem to be talking about "what will be the result if a real world magnetar collapsed into a black hole, given an assumption that it is immersed in a plasma environment."
Again, where did I say a charged black hole is impossible? I specifically said in extreme cases at the very beginning.
Nice paper, but they made approximations. Specifically, following equation 24, they assume epsilon is positive. This is true for an uncharged black hole, but I'd like to see it justified if they think it's still true for a charged one, particularly an extremal one.
Then read on, because as is typical they start with the case of no spin, no charge and then add those terms in. Specifically equation 34 and table 1 address this very issue.
Re: So how do you detect one? (Score:1)
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If there are no obvious gravitational effects at the event horizon, what is the mechanism for detecting such a thing?
Gravitational effects vanish at the event horizon, but not outside the event horizon.
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The effects at a distance are pretty obvious. An extremal charged black hole would have a huge charge, which would have massive effects on anything around it. Similarly, we can measure the spin of a black hole by observing the effect it has on its surroundings.
If nature allows it, it exists (Score:2)
> "Just because a mathematical solution exists that has nice properties doesn't necessarily mean that nature will make use of it," Khanna said. "But if we somehow find one, that would really [make] us think about what we are missing."
I'm going to vote for an issue with our current understanding of physics, because supermassive black holes without surface gravity floating around the cosmos would be swallowing up mass and effectively erasing gravity as it went. There would have to be a signature left behi
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If they have no surface gravity, WOULD they be swallowing up things? Probably to some small extent, via collisions, but probably an extremely small extent.
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With diameters measured in AU, still probably mostly misses, but they'd never be deflected either.
And somehow I really have trouble with the concept of gravity disappearing because of charge. That would mean that charge can manipulate gravity, but we've only seen that in terms of mass where charge is irrelevant and we've never seen any change in gravitational fields due to high charge.
Even if we don't have powerful enough tools or delicate enough instruments to experiment with that on Earth, you'd think th
Re:If nature allows it, it exists (Score:5, Interesting)
And somehow I really have trouble with the concept of gravity disappearing because of charge. That would mean that charge can manipulate gravity, but we've only seen that in terms of mass where charge is irrelevant and we've never seen any change in gravitational fields due to high charge.
As well you should have problems with that. Of course, charge can add energy to the Hamiltonian/Lagrangian, so you'd expect an effect on the gravitational field.
But the summary doesn't say that gravity "disappears"; you should read it as "the force produced by gravity is counteracted by the combination of electrostatic forces and an accelerated reference frame (centrifugal forces due to the spinning)".
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With diameters measured in AU, still probably mostly misses, but they'd never be deflected either. And somehow I really have trouble with the concept of gravity disappearing because of charge. That would mean that charge can manipulate gravity,
Correct, and this is part of Einstein's General Theory of Relativity. Gravity is produced by the stress-energy tensor, which includes both the E and B fields, as well as other contributions, such as pressure and momentum. See: Electromagnetic stress–energy tensor [wikipedia.org].
but we've only seen that in terms of mass where charge is irrelevant and we've never seen any change in gravitational fields due to high charge.
We have gotten nowhere near the levels of electric fields needed to measure gravitational effect of charge.
Even if we don't have powerful enough tools or delicate enough instruments to experiment with that on Earth, you'd think there'd be something astrophysical we could point a telescope at and test this.
Objects in space tend to not be highly charged, because charge is self neutralizing. (This is a significant difference between mass and
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Relativity and QM are both empirical. We rely on them on a daily basis. Relativity has to be factored into satellites for them to work; QM is the only reason any piece of electronics you own works.
But your criticism works after that point. Theorists and mathematicians have been trading semantics for half a century with effectively zero advancement
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But your criticism works after that point. Theorists and mathematicians have been trading semantics for half a century with effectively zero advancement in real-world understanding.
You've apparently forgotten entirely about information theory, the development of non-equilibrium statistical mechanics, quantum field theory (as extremely distinct from "QM"), and all of their implications for computation, biology, integration through models, the reinvigoration of Bayesian statistics, and the like.
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If the tools are basically correct, why would you expect them to be "revolutionized"?
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We have very little understanding of physics currently. Instead what we have are mathematical delusions piled one atop another. And each generation of physicist just getting more and more confused and deluded than the last.
One has to go all the way back to classical newtonian physics before one comes across actual useful principles that can be relied upon in the real world.
The sooner we understand this and the mathematical house of cards comes tumbling down the better.
Silly. The apex of classical (not Newtonian) physics is the Principle of Least Action, which also applies to every other aspect of physics (why? That's unsure, but it's unsure why it applies to classical physics as well), and which supplies a very nice route into QFT. It's cute that you'd call this a mathematical delusion, as it is /the/ most useful path through ALL of physics.
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Gun, consider yourself jumped (Score:3)
This is pretty interesting, if true. But both of these papers are currently on arxiv - meaning they have neither been peer-reviewed nor published yet. So before making dramatic claims based on them, let's first see if they stand up to scientific rigor.
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This is pretty interesting, if true. But both of these papers are currently on arxiv - meaning they have neither been peer-reviewed nor published yet. So before making dramatic claims based on them, let's first see if they stand up to scientific rigor.
If they can stand up to the gravity of a black hole, that should be easy!
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In physics it is common to put a copy of papers on arxiv that isn't reviewed, whenever your paper has been reviewed and published. It is technically not the same paper, though all the text and illustrations are identical ;)
Re: steven hawking was wrong. full stop. (Score:2)
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"it's an interesting thought." No, it isn't. It is idle speculation. I cannot prove X, therefore X is possible.
Notice any stumbling blocks in this phrase? (Score:1)
Two experts in information language, studying empirical reality, have concluded that nothing in their language offers any conclusive evidence on the physical question one way or another. Well done! Surely next to win publication and accolade: Have two linguists say that their studies of Proto-Indo-European in no way precludes the possibility of there being a massive undiscovered prehistoric city under Prague, and publ
Dear Lort (Score:1)
Re: Dear Lort (Score:1)
It's not full of stars (Score:2)
In 1973, the prominent physicists Stephen Hawking, James Bardeen and Brandon Carter asserted that extremal black holes can't exist in the real world
Apparently they're unfamiliar with my career.
Einstein once said singularities didn't exist. (Score:2)
He acknowledged that his own theory of relativity itself predicted their existence, but he believed them to be a mathematical oddity, not a real physical possibility. Since then, there have been more than a few theoretical constructs which have been given the same treatment (wormholes, anyone?).
Singularities? Well, we found those, turns out they were more than just a case of arithmetic gone mad. Wormholes? Jury's still out on that one. I get the impression that this type of singularity occurring natur
Ahem (Score:1)
This is a beautiful example of math giving back to physics
Ahem, giving "back" to Physics? Like mathematics owes its existence to Physics, and occasionally "giving back" is something that happens rarely enough that it needs to be called out?
I think it's the other way around.