Have Scientists Finally Made Sense of Stephen Hawking's Famous Black Hole Formula? (science.org) 26
Slashdot reader sciencehabit shares this report from Science magazine:
Fifty years ago, famed physicist Stephen Hawking wrote down an equation that predicts that a black hole has entropy, an attribute typically associated with the disordered jumbling of atoms and molecules in materials.
The arguments for black hole entropy were indirect, however, and no one had derived the famous equation from the fundamental definition of entropy — at least not for realistic black holes. Now, one team of theorists claims to have done so, although some experts are skeptical.
Reported in a paper in press at Physical Review Letters, the work would solve a homework problem that some theorists have labored over for decades. "It's good to have it done," says Don Marolf, a gravitational theorist at the University of California, Santa Barbara who was not involved in the research. It "shows us how to move forward, that's great."
The arguments for black hole entropy were indirect, however, and no one had derived the famous equation from the fundamental definition of entropy — at least not for realistic black holes. Now, one team of theorists claims to have done so, although some experts are skeptical.
Reported in a paper in press at Physical Review Letters, the work would solve a homework problem that some theorists have labored over for decades. "It's good to have it done," says Don Marolf, a gravitational theorist at the University of California, Santa Barbara who was not involved in the research. It "shows us how to move forward, that's great."
Have they asked ChatGPT for confirmation? (Score:1)
It won't know the current result, because that came after it's training cut-off, but that's all the better: It can't copy the result, so it has to derive it from the fundamental equations. Gotta be sure.
What the original article doesn't mention is (Score:5, Interesting)
Re:What the original article doesn't mention is (Score:5, Interesting)
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"The quantum hair theory is a bald lie!"
Black Hole? (Score:1)
I call it a Hawking Hole.
Hypothetical question (Score:3)
Thought problem for the physics mavens here.
The event horizon is usually described as requiring an escape velocity faster than the speed of light, and anything that falls in can't get out.
Suppose an object came in on a parabolic or hyperbolic course, in the manner of a meteor or comet going around the sun. Ignore tidal and time dilation effects for the moment because that's something the object will experience and I want to view this from a reference frame outside the black hole.
Suppose the orbit of the object goes inside the event horizon at an angle, so that the object wouldn't intersect the singularity at the middle.
Would it come out again?
In Newtonian terms the object would speed up as it approached the black hole and crossed the horizon, and it could never exceed or attain the speed of light, but would get kinetic energy in excess of it's actual speed. Things appear heavier as they are accelerated, and more and more of the energy is put into mass while the velocity only approaches the speed of light.
Coming around the object the same process happens in reverse, so the object isn't travelling at escape velocity but the pull from the singularity takes mass energy instead of slowing the object down. Without slowing down appreciably, the object should pop back out of the black hole and continue on it's original course.
Is there a good reference that points out the fallacy in this argument? I'm just a little surprised that there's this area in space that will grab anything that flies by and suck it in permanently. Especially since the black hole has roughly the same mass as a regular star, so flying around in the vicinity should be no more difficult than flying around in the vicinity of a typical star.
(I've been looking into whether the universe is computable, and the existence of boundary discontinuities 'kinda throws a wrench into those theories.)
Is there a good reference online that explains this?
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Due to that Einstein dude, it doesn't have enough time to get out again.
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So you just need to substitute "photon" for "object" in your question and take into account that it moves at light speed, and then you have the answer.
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My thought experiment is, what if two black holes were approaching each other very rapidly on a not-quite-collision course, so that the sides of their event horizons briefly overlapped as they passed. Would they stick together?
ISTM that if anything was inside the overlapping area they'd have to stick, since otherwise that thing would be escaping from one of them. But is there anything there? Maybe something that just now fell in and hasn't had time to fall to the center? Or, is there quantum foam inside
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These two black holes wouldn't stick to each other, but start swirling around each other and eventually merge together.
This is partly because of friction with and among other stuff in orbit around the black holes in their "accretion disks". (Black holes experience friction by eating the stuff in the other hole's disk of debris, with the momentum of the black-hole-plus-dinner thus being different from the black-hole-before-dinner.)
It's also partly because the rapid acceleration of things passing near a blac
Well, most of it... (Score:2)
Anything that goes slow enough to be captured into an orbit will eventually spiral inwards.
Well, most of it (when we're talking matter not already in another black hole). Ordinary stuff orbiting near a black hole gets torn apart by the enormous tides and forms a disk-like structure similar to a gas giant's rings. Interactions among it and with the black hole's magnetic and gravitic fields can eject a bit of it in a pair of jets out along the axis of the disk, powered apparently by the rest of the stuff fa
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Short version : I don't think your idea works, but it was worth an hour of thinking and typing. The details have vanished into Cloudflare's bit-bucket. Sorry. Blame Slashdot.
I should remember to copy-before-submitting. But the blame is still on Slashdot.
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Do you ever not get the "this check is taking longer than expected" warning? It normally takes several minutes for that page to load for me - I assume it doesn't like my mixture of ad-blocking and NoScript. Which is Cloudflare/ Slashdot's problem, not mine. If they don't want comments, comments they won't get.
Does Slashdot actually have advertising? I've had that "Advertising disabled because
Re:Hypothetical question (Score:4, Informative)
Re:Hypothetical question (Score:4, Interesting)
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PS: Alternatively, you can imagine to unroll the time-space-curve around the Black Hole into a flat surface, and if you then plot the hyperbolic curve of your object onto that flat surface, you will notice that it winds infinitely often around the singularity before leaving the Event Horizon.
Ah, a -funroll-loops solution to a Slashdot problem.
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I
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No, the part he's missing is the idea that one can't model this while ignoring time dilation. Not even approximately accurately.
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It might break the speed limit. For tarmac roads. Small-integer fractions of c ? I don't think so.
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Your scenario is fallacious. You can’t ignore things like time dilation. The situation is not Newtonian. Time dilation is not something the object experiences, it’s something you would see as a faraway observer.
As a viewer far away you would see the object slow down as it approaches the event horizon, and freeze there forever, never crossing it.
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If light, the fastest moving thing in the Universe, can't get out, then neither can a slower moving thing.
The best reference for this is to start with a good modern physics class and the