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Why the Black Hole Information Paradox Is Such a Problem
New submitter TheAlexKnapp writes: Here's a really nice explanation of the Black Hole Information Paradox for those who are unfamiliar with it. The article lays out the basic gist — that right now if you take two black holes, one made from the collapse of one type of star, and the second from the collapse of a different type, you can't tell which is which. Ethan Siegel points out that Hawking's big announcement was really just a small step heading towards a possible solution, and highlights that the paradox highlights the incompleteness of our understanding of some types of physics.
Leonard Susskind discusses this in a talk he gave a few years ago.
https://www.youtube.com/watch?v=2DIl3Hfh9tY
Pretty entertaining.
You do know. There's information on and within both phones that's a record of which owner they had.
What if I make two different ice sculptures from the same source of water with the same mass but different shapes. After they melt it's impossible to tell which one was which. That's not a paradox.
Of course you are simplifying down to a ridiculous level, and I do understand that information is a pretty powerful concept in physics that carries a lot more weight than you would think, but still, I did not find anything useful in this article. The title of the Slashdot Summary was very promising: "why the black hole information paradox is such a problem", so I was hoping to finally see this question answered, but no, same old same old. Information gets conserved in all experiments we do outside black holes, so we kind of assume this must be some cosmic requirement (why?), and for some reason which is never properly explained we just can't accept that black holes would destroy information. Because... well, why exactly? Why is it such a problem that information would simply disappear in a black hole?
Why would it be such a problem if information did simply disappear? Oh my god, entropy might go down in an isolated system, it's the end of physics as we know it! No it's not. Entropy is just a trick that works because of the statistically enormously small probability of it going down in a large macroscopic system without spending energy on it, but isn't that really all it is? Why does it get treated like one of the most important truths in the universe?
In general relativity (our theory of classical gravity, without quantum effects), there are several "no hair" theorems, saying that several types of black holes are completely determined by a few overall parameters (say mass, charge and angular momentum) and without regard to their history.
We don't yet have a theory of quantum gravity, so we don't know if the quantum state of a black hole does retain information. It probably has to, but this is not understood. By the way, in any case classical GR would be an excellent approximation except in the case of very small black holes, so any information retained will not be actually accessible.
Black holes are just a toy.
Suppose gravity wins out after all, and the universe ends in a Big Crunch. One or a few Planck second(s) before the singularity, all the information in the universe should still be there. How?
Suppose entropy wins and the universe ends in heat death. For bonus points assume all protons have decayed. All the information should still be preserved. How?
When the copyright term is "forever minus a day", live every day like it's the last.
Obvious non-physicist here, but in absolute terms, information theory says that the original systems' (ice sculptures) information -- every particle's directions etc. was not destroyed, though it may be terribly difficult to ascertain by us at a later time.
I don't pretend to understand why, but the fundamental premise is that information is a conserved property.
Pretending this is my office full of bitter coworkers..
No, it is more subtle than that. Conservation of information is closely tied to time reversal symmetry and energy conservation as a result of Noether's theorem. But in general it is not tied to casaulity.
I'm not an astrophysicist either but I think that your mention of ice sculptures hits the nail on the head. When an ice sculpture melts the organization of the ice vanishes. But it also cools the air. The information content of the cold air increases. So the answers is the system preserves the information. Likewise when something is sucked into a blackhole it contributes it's mass but the organizational information it had (position, momentum, internal quantum states) is gone. On the otherhand as it's charges separate and accelerate it radiates and that radiation disturbs the rest of the universe. Thus my non-astrophycist guess is that those two exactly balance just like the ice sculptures warming chills the environment.
Some drink at the fountain of knowledge. Others just gargle.
Until then it sounds like: just because you can reverse some signs and run your equations backwards doesn't mean that all math has a physical reality.
Nope, Noether's theorem is quite specific, and if there are certain symmetries in your equations (i.e. you can just reverse some signs for on example), then there exists certain conservation laws. If there is time symmetry in the equations, then it is a necessary consequence of the equations that energy is conserved. This has nothing to do with reality of math or if time can actually be reversed... either the particular equations are correct or not. If they are correct, then all logical consequences of the equations are also correct.
For every unique cause is a unique effect. You can know what the cause was based on the effect. If the effect disappears, you can't know what the cause was. Anyway, if information is destroyed, that means the energy it represented is destroyed which means it cannot contribute to the mass of a system. It's contradictory to say the mass of a blackhole increases if the information is destroyed. A blackhole is created by too much information and it is itself a blob of information. The question isn't "why does a blackhole destroy information", but "what mechanism does a blackhole use to allow information to be recovered".
Yea, I don't see why this is a problem, anymore than any other thing in physics today.
I think what they're trying to say is: "Black Holes Matter".
*ducks*
You were critically hit for no damage. The bruise will look nice, and maybe the scars will make good party talk.
So when the black hole evaporates by giving off Hawking radiation, who's to say the information (albeit all mixed together) isn't coming out in the particular spatio-temporal pattern of emanation of the radiation?
Sure, the radiation seems (and is effectively to any observer) random, but it is well known that a random bitstring (k-random bitstring) can encode information, and in fact can be the most compact encoding of information.
Random simply means you don't have the means or supplementary information to deduce/detect the pattern. It does not mean that no pattern is there.
Where are we going and why are we in a handbasket?
Susskind wrote a very interesting book on this topic, too. The Black Hole War, subtitled, "my battle with Steven Hawking to make the world safe for Quantum Mechanics". I was hoping someone in the thread would know if Steven Hawking's announcement was an acceptance of Susskind's position, or similar to it, or something else.
Thanks for clearing that up. I can get back to my facebook updates now.
When all you have is a hammer, every problem starts to look like a thumb.
From Stephen Hawkings notes:
"And then I was reading slashdot and anonymous coward said all of this preservation of information stuff is a laughable concept, that's why I've switched professions from math/physics to web site dev. I'm working on a website for balancing checkbooks, should be really cool."
(Assuming I have this correctly.):
A rule of physics had been that information is not destroyed. (It can be scrambled beyond recovery by any reasonable process, but it's still there.)
Black holes make the information inside them inaccessible - no message gets out. Ok, it's still there but you can't get to it. All you can measure about a black hole is its mass, electric charge, and spin. All those other quantum numbers get hidden.
But Hawking radiation - according to the first formulation - is vacuum virtual particle pairs, appearing near the event horizon, where one got trapped by flying through the event horizon, releasing enough extra energy for the other one to become permanent and fly up the gravity well and away. The lost energy of the particle creation and ejection comes out of the total mass/energy of the black hole, so it shrinks a bit.
It's almost as if a particle tunneled out of the hole, but not really. The type of particle pair is random. If they're charged, the electric field can bias the probability of which one falls in, gradually discharging the hole. But the other fields don't leave memory, so, for instance, you get equal amounts of matter and antimatter, regardless of what you originally squeezed into a black hole.
But the evaporation of the hole leaves nothing behind. So if you built the hole out of mostly anti-matter you get half of it back as antimatter and half as normal matter, changing the matter/antimatter balance of the universe.
Oops!
(If this is correct, perhaps the explanation for the predominance of normal matter in the observed universe is that more anitmatter than matter got squeezed into early black holes, to emerge, if at all, as 50/50? You heard it here first!)
Matter/antimatter and related conservation of this-and-that laws is part of the information that's not supposed to go missing. Even if you DON'T violate those conservations, Hawking radiation was supposed to be random. So when the black hole evaporates (in a blaze of glory right at the end), all the information that went beyond the event horizon is still lost, replaced with an equal amount of purely random noise.
There has been a big discussion in physics on whether the information actually is lost. It got a LOT hotter when a scientist computed how much information should be inside the event horizon of a black hole and discovered that it was exactly proportional to the area of the event horizon, at one bit per plank-length-scaled patch. This led to speculation that maybe the infalling information doesn't actually fall in, but "gets stuck" on, or just above, the event horizon and might be returned to the rest of the universe during the evaporation process.
There were different camps on this, with Hawking being in the "lost" camp and others (including Susskind, who gives public lectures to laymen) in the "maybe it's not lost" camp.
Now Hawking may have been convinced, or convinced himself, that maybe the info isn't lost, and switched positions on the argument. This is big news.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
remembering the future is not something we do since the brain has not had that information enter the brain yet, you could remember the future if you used equations and a computer program that predicted the future and fed the future into your brain - this was sort of Leibniz's dream that all of the universe could be calculated by equations and all arguments could be sorted out using equations. Essentially Leibniz was a computer programmer predicting Google before computers even existed.. he invented calculus ironically at the same time as Newton did.
maybe information gives us the illusion that there is physical matter here... If you were the character running around in grand theft auto and you bent down to touch your shirt pocket, does your shirt pocket actually exist physically in grand theft auto? The information is stored on a hard drive and in the computer memory, but the character inside grand theft auto doesn't have an actual shirt that he is touching... So if you give the character A.I. where he can think about his universe, does he think his shirt is information, or is it physical?
You and who ever modded up this post should do said reading. Quantum fluctuations, virtual or not, do not violate conservation of energy and do not make the universe any less closed. Work like QFT that takes these into account, producing some of the most accurate quantitative predictions ever in physics, basically show that what we see and measure already includes the effects of the vacuum, including on the microscopic level.