Physicists Observationally Confirm Hawking's Black Hole Theorem For the First Time (mit.edu) 53
Fifty years later, physicists at MIT and elsewhere have now confirmed Hawking's area theorem for the first time, using observations of gravitational waves. Their results appear today in Physical Review Letters. MIT reports: A central law for black holes predicts that the area of their event horizons -- the boundary beyond which nothing can ever escape -- should never shrink. This law is Hawking's area theorem, named after physicist Stephen Hawking, who derived the theorem in 1971. In the study, the researchers take a closer look at GW150914, the first gravitational wave signal detected by the Laser Interferometer Gravitational-wave Observatory (LIGO), in 2015. The signal was a product of two inspiraling black holes that generated a new black hole, along with a huge amount of energy that rippled across space-time as gravitational waves. If Hawking's area theorem holds, then the horizon area of the new black hole should not be smaller than the total horizon area of its parent black holes. In the new study, the physicists reanalyzed the signal from GW150914 before and after the cosmic collision and found that indeed, the total event horizon area did not decrease after the merger -- a result that they report with 95 percent confidence. Their findings mark the first direct observational confirmation of Hawking's area theorem, which has been proven mathematically but never observed in nature until now. The team plans to test future gravitational-wave signals to see if they might further confirm Hawking's theorem or be a sign of new, law-bending physics.
Hawking radiation (Score:3)
I thought Hawking radiation enabled a black hole to lose mass, albeit slowly.
Does that not also shrink the event horizon?
Is this one of those relativity vs QM contradictions, bad reporting, my misunderstanding, or something else?
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I thought Hawking radiation enabled a black hole to lose mass, albeit slowly. Does that not also shrink the event horizon? Is this one of those relativity vs QM contradictions,
Yep.
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Re:Hawking radiation (Score:5, Informative)
oh they do get smaller according to that theory, the radius of a black hole is always twice its mass in Planck units. But that takes immense amount of time. The smallest possible collapsed star black hole, with about 4 solar masses, would take about ten to the 69 power years to evaporate.
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Yes it matters, because theory of article is only a General Relativity thing, on scale of age of universe ( and many many multiples of that) it's true. It's not a claim about any quantum process that eventually would make a hole smaller, that's not here in the GR class but in Quantum Mechanics 604 down the hall.
it would be immense discovery to detect Hawking radiation, could help make a theory that unifies GR with QM... but of course any black holes we actually know about are just too damn big to detect
Re: Hawking radiation (Score:1)
It goes rather quickly, if your black hole is tiny. :)
Ask the LHC team. :)
Or our planet, which "catches" 3 tinly black hones a day.
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that's just one speculative theory that says tiny quantum black holes might occasionally be produced at LHC (and go *poof* in less than a femptosecond)
Ditto for any hitting the Earth, just an unproven hypothesis.
Detection of a black hole even with mass of our sun would be massive huge discovery, because that would be "tiny" one too, not produced from star but perhaps from early universe.
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That's the theory anyway - only problem is the theory is based on a *major* untested assumption: that black hole evaporation continues normally at the quantum scales. And we currently have NO quantum theory of gravity on which to base that assumption. The incompatibilities between QM and GR are one of the major reasons we know that at least one of the theories is incomplete.
There's also a paradox created if a black hole can completely evaporate: QM insists that information cannot be destroyed, while the
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that black hole evaporation continues normally at the quantum scales. And we currently have NO quantum theory of gravity on which to base that assumption.
It has neither anything to do with GR nor gravity nor QT.
I suggest to google "Hawkings Radiation".
For a laymen: in the universe we assume that the vacuum creates constantly particle pairs, which decay instantly, e.g. when an anti electron hits an electron.
At the edge of a black hole exotic particles get created, some with positive and negative mass, e.g.
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I believe the issue is that Hawking radiation is currently described in terms of a quantum particle pair interacting with a well-defined classical event horizon. Which, especially as you approach an atom-scale black hole, requires that the mass it's made of has a well-defined location. Meanwhile QM asserts that the location and energy (mass) of particles (including black holes) cannot both be simultaneously well-defined.
There's also the plank-length to consider as a confounding factor. Current theory is
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Basically, the information about everything a black hole has absorbed is permanently trapped within it - which is okay according to QM, but if the black hole completely evaporates there's no longer any place for that information to be stored, and one of the fundamental precepts of QM would be violated.
There is no such "percept" of QM.
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Technically you're right - Conservation of Information is part of Quantum Field Theory, which is the far more accurate and predictive successor to the original "simple" Quantum Mechanics.
https://van.physics.illinois.e... [illinois.edu]
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Unknown if any of that applies to black holes though. A real black hole with quantum behavior might not even have an event horizon, might not have singularity.
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Well, we have zero reason to believe that singularities actually exist anyway. The event horizon though is the defining property of a black hole. Without it you have... something else. And at this point we're pretty sure that:
A) Real black holes do in fact exist (Those recent direct photos of a lopsided doppler-dimmed accretion disc with a characteristic BH "shadow", while not conclusive due to the extensive image processing used, are still quite compelling)
B) *All* gravitational attraction *must* exhibit
Re:Hawking radiation (Score:4, Interesting)
It is all down to spin and we ain't talking marketing. How fast that black hole spins. It it ain't spinning enough it does not lose mass, the faster it spins the more mass it loses but it is losing mass in a quantum state which does not become normal space matter again until it crosses the event horizon.
They are likely to grow and shrink but it would be really slow, really slow, they are always sucking up matter from around the equator and only losing it at the poles. They lose it more quickly at the poles when they gain it more quickly at the equator.
Shrinkage would have to be from a particularly mass depleted region and occur over a very significant amount of time. As the area for accretion is far larger than the area for loss and the spin must be fast enough. If not it likely just keeps expanding until it goes boom, it distorts the ability for it to exist, the entire mass expands into a quantum state at the speed of gravity and when the energy for expansion collapses, it doesn't collapse so much as the gravitational chain reaction ceases and the quantum state matter accreates to a cloud of high energy particles that form together over time, hollow galaxies. An entire galaxy with limited spin.
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PS when it is spinning real fast, the surface on either pulling on the centre, weird things will happen in that centre, mass pulling it together, whilst pulling it apart. Think of the mass spinning at the equator, anything beyond the centre, pulling at that centre, whilst the mass around the equator pulls it together. Those are really high forces and energy levels at the centre, logically powerful enough to pull matter completely apart and revert it to a quantum state, where it is not longer affected by gra
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"no spin is catastrophic."
Why, whats it going to do? It can't explode, gravity will see to that.
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Absolute BS.,/p>
The fact of the matter is that Hawking proved that nonspinning black holes radaite
Re: Hawking radiation (Score:1)
No, he did show it, mathematically. :)
Mathematics is not reality.
You still have to actually observe it, to pass the treshold from useless mere beliefs to useful science.
I am not sure if the LHC team did that already. Anyone up to date about that?
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I mean, I'm sure its true, smarter men (or rather men with qualifications) than me. But I always thought the 'event radius' was synonymous with the Swarzchild radius.
And since thats R = 2GM/C^2, and G (Gravitational constant) and C (speed of light) are both universal consants, leaving the only independent variable being mass, then surely losing mass means losing radius.
But apparently not?
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Only true for black holes that are chargeless and massless ie Schwarzchild black hole.
Re: Hawking radiation (Score:1)
It's "Schwarzschild", by the way. No children in there. ;)
"Schwarz" means black. (Alternative archaic spelling "Schwartz".)
"Schild" mean "shield" (In every sense. And "sign", as in roadsign etc).
So "black shield radius". Very well chosen, I think. :) :)
Much better than "dark *" or "big bang".
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Also true for spherical chickens in a vacuum.
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And since thats R = 2GM/C^2, and G (Gravitational constant) and C (speed of light) are both universal consants, leaving the only independent variable being mass, then surely losing mass means losing radius.
Correct. But the article here is about the sum of the masses of two black holes, when they collapse into one.
They radiate away energy (and hence mass) in the form of gravitational waves, so the total radius is less than the sum of the radius of the two individual holes. But Hawking's area theorem says that the total surface area can't decrease, so the resulting black hole can't have a radius less than SQRT(r_1^2+r_2^2).
But apparently not?
Right. The area theorem is classical relativity (and thermodynamics: it is the equivalen
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As usual, the real explanation is buried in the comments.
Today is the first day in weeks I haven't had mod points, or this would be given +1 Informative.
Instead I'll point anyone else looking for a concise and accurate explanation to the above comment.
Thank you, Mr. Landis [geoffreylandis.com]! I didn't know you existed until now, but I'll be reading!
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In fact, almost every star black hole now is cooler than the background noise so it is growing absorbing cosmic radiowaves.
But technically, yes. It could loose mass. In a future where the universe will be cooler.
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>They can lose mass, but apparently do not get smaller.
Nope. The Area Theorem is pure classical physics, while Hawking Radiation was discovered later when he considered how Quantum Mechanics would interact with the event horizon. But Hawking Radiation is so miniscule for a remotely stellar-mass black hole that the effective temperature is far lower than the CMBR, so even the most isolated black hole will still absorb more energy from the CMBR than it radiates away.
You'd need a black hole with considera
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>I thought Hawking radiation enabled a black hole to lose mass, albeit slowly. Does that not also shrink the event horizon?
>Is this one of those relativity vs QM contradictions, bad reporting, my misunderstanding, or something else?
I had the same question and did some searching. It sounds like basically Hawking's Area Theorem is based entirely in classical physics, and was later superseded by Hawking Radiation, which is based in Quantum Mechanics. So not so much one of the fundamental contradictions
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Nice FP question. Wish I could give you the other Insightful mod you deserve.
Normally volume is conserved (Score:2)
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Radius
Area
Mass
Volume
He is pointing out the non-intuitive nature of black hole density. The larger a black hole is, the less dense it is (density is mass divided by volume, but these do not grow linearly with each other!), and in the mid-20th century there was still a theory that maybe all the matter in the universe was densely packed enough to form an even horizon, the average density of the black hole thus formed would exactly be what we obse
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Umm... what?
For black holes the accepted theory is that mass and radius DO grow linearly with each other. The formula for the Scwarzschild radius is
r=M * 2G/c^2
where M is the mass of the black hole and the rest are constants
And of course, with normal (incompressible) matter, mass and volume grow linearly with each other: m=pV, where p is the density of the material.
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The Schwarzshield Radius is the Event Horizon.
And has nothing to do with the black hole itself.
The black hole in the center is in infinite dens "black thing", a singularity. Around it is a lot of empty space, unless an aggregation disc is around it.
And: the Schwarzshield radius - aka the size of the sphere from were nothing can escape - is far far out.
In theory you could have suns and planetary systems orbiting a black hole inside of the schwarzshield radius.
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Generally speaking "black hole" refers to the event horizon - the part that can be seen and measured, at least indirectly. Which is why we can speak of the "size" and "density" of a black hole - a singularity would be sizeless and infinitely dense. Which is a red flag that we probably don't actually understand what's going on inside the event horizon - when a real-world application of theory generates an infinity as a result, it's always previously turned out to be a symptom of an incomplete theory.
That a
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I was wondering if there was some theorem that said that the amount of emitted radiation always results in the area of the final black hole being the sum of the areas of the initial black holes.
Nope. The theorem only says that the area can't be less than the sum of the areas. (And, of course, the radius can't be greater than the sum of the radii. So it puts upper and lower limits on the radius of the combined hole).
A sink hole? (Score:2)
Haven't studied physics beyond high school, so go easy on me here, but if something consumes something else without changing size then it sounds like a sink hole.
Maybe that image comes to my mind from the various visual representations I've seen around of black holes that illustrate how they bend space time.
Is that a correct assumption and can someone who knows more elaborate please? Thanks!
Re: A sink hole? (Score:1)
Technically, everything inside the event horizon resides temporally *after* the end of the universe / "end of all time".
So technically, that's where the sink hole would lead to. Which technically could be a white hole aka new universe / big bang.
Obviously, this is rather ... hard ... to verify. ;)
PBS SpaceTime has some amazing episodes on that topic. Including imagining a spaceship that would fly into a black hole, our a black hole, and then some even more weird things like parallel universes inside other b
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Who said it doesn't change size?
The theory just says the area doesn't *decrease*, it can still *increase*.
With normal incompressible matter, combining two spheres into one would decrease the area:
Area ~= r^2
Mass ~= volume ~= r^3
so a sphere with double the mass increases the radius by a factor of 2^(1/3) = ~1.26
which increases the area by 2^(2/3) = ~1.59
Which is considerably less than the 2x the surface area that two separate balls have.
For black holes though, radius scales linearly with mass, so twice the m
It is just one data point... (Score:1)
How could we "confirm" theory having just single data point?
It is better than string "theory" which has 0 data points but still...
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TFA quotes the scientist, there can be a zoo of compact objects so this is not a one and done confirmation, just the beginning of lots of similar experiments
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No, it's one collision; thus one data point in the (final mass) as a function of (initial mass) experiment. It took many experimental data points to get the wave shape that allowed them to compute that measurement, of course.
The answer to the original question is, yes, the one data point confirms the theory, but one data point confirming the theory does not prove the theory. No amounts of confirming data points will actually prove a theory, since one data point that fails to match the theory will disprove
...just wow... (Score:2)
So when you add black holes, they never subtract ?
Who knew ?
He must have came to this after heavy joint...
A question. (Score:1)
Re: A question. (Score:2)
Yes, and the matter directly outside of the event horizon, which still *can* escape, but accelerated to insane speeds. Plus Hawking radiation, but we could only measure that very *very* up close (like millimeters), I think.
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Is the energy mentioned in the article only expressed in form of gravitational waves?
Exactly right.
The gravity of a black hole does extend outside the event horizon, of course, and hence if you jiggle the black hole (by, say, passing another black hole near it), you emit gravitational radiation which radiates energy.
If you like, you can say that the radiated energy comes from the potential energy released as one black hole slides down the gravitational potential into the other black hole.
But if Hawking radiation exists... (Score:1)
...it *did* shrink.
By a tiny amount, due to its huge size, but still...
It's the only reason Earth still exists. Otherwise the ~3 tiny black holes that enter the athmosphere each day would not have quickly "evaporated" and the LHC would definitely already caused the end of the planet. Sadly, it did not. :)