Main Question or Discussion Point
can someone explain information loss paradox in layman terms without using any quantum physics terms...i read in some sites but i couldnt understand as they are explaining using some jargon terms...
I do not think that it is correct. GR is a causal theory. In principle, from the exact state of a classical black hole at a FINITE time after the start of collapse, you can reproduce the initial conditions of matter that were present before the collapse. (This is analogous to the fact that if you take a porno picture and cut it in a million of pieces and mix them all up, your mother/girl friend/wife can still reproduce the original picture. )GR says the information is gone.
Since when is this true?… the principle of microreversibility, which has always held in classical and quantum physics, …
Perhaps the information is stored on the surface of the black hole as waves generated by what and how objects fall onto it. Afterall, two black holes merging are not expected to instantly form a perfectly symmetrical sphere, so there would be peaks and valleys associated with how they merge, right? Then the radiation would be correlated to these waves on the surface which would reflect information about what fell in. Does this sound plausible? just guessing.Now, what is the solution of the paradox? To be clear, there are many proposals and there is no consensus among experts.
I think the problem that underlies all these primarily philosophical issues is that people continually treat any branch of physics, be it quantum mechanics or classical mechanics, as if they were intended to be, or succeeded as, axiomatically complete descriptions of reality. But they weren't, and they aren't. In quantum mechanics, there is no evidence at all that we gain insight into a macro system by describing it with a "wave function" (except insofar as one recovers the classical principles that underlie quantum mechanics), and in classical mechanics, we already know that the concept of an "exact trajectory" is inconsistent with precise observation. But above all, both of those theories are reversible in time, so we had to invent an entirely new approach, thermodynamics, to treat very complex systems. Now, who among us can claim the concept of "irreversibility" is not vastly effective at treating much of reality (and allows the patent office to duck the endless stream of perpetual motion inventions)? Yet this concept appears nowhere in either classical or quantum mechanics. If someone says, "there's no such thing as irreversibility in principle", I say, "you have a different interpretation of what a principle is than I do-- because I think irreversibility is as valuable a principle as any!"That is to say toss an unopened deck of cards into the Sun and by looking at the end products of the incineration we could determine the information printed on the cards to tell if it was a Poker or UNO deck of cards?
In principle that may be true for a Classical interpretation.
Actually, almost the opposite is true. The gravitational field is about the only thing a black hole has in common with a star.the only difference between blackhole and other other heavenly bodies like earth,moon is the heavy gravitational field...
A black hole doesn't have a surface.if we drop some thing like my hard drive on earth it will be on the earth's surface and if we drop it on moon it will be definetely on the moon's surface...likewise the same hard drive should be on the blackhole's surface,isn't it?
The hard drive can't come back in one piece from the region inside the event horizon, and its mass must eventually come back in the form of Hawking radiation. You got those details right, but it's still far from obvious that the information stored on the hard drive will be present in the radiation.then how GR says information is lost ...information is on the blackhole's surface,am i right?only difference is that hard drive cant come back to our world since the escape velocity is greater than c....and after some time because of hawking radiation my hard drive will come back to our world i think else law of conservation of energy would be violated...clear my doubts..
The geometry of space-time around the black hole will contain information about the matter that collapsed, but it won't contain all of it.In principle, from the exact state of a classical black hole at a FINITE time after the start of collapse, you can reproduce the initial conditions of matter that were present before the collapse.
I don't think the idea of a zero mass black hole makes sense.Quantum black hole creates pairs of particles. One of the members of the pair escapes from the black hole, while the other falls into the black hole and remains there. During this process the outside energy increases (due to the particles that escape), so the total energy conservation implies that the inside energy must decrease. Eventually, the energy of the black hole drops to zero. GR says that the black hole with zero mass contains nothing, i.e., that its information content is zero. On the other hand, this zero mass black hole should still contain the information carried by particles that fell into the black hole and remained there, i.e., the information content should not be zero.
He didn't say that they are. I haven't read his article recently, but it seems to me that all he says is that time evolution is reversible in both theories.From the Leonard Susskind article: Since when is this true?
QM and classical are not the same thing!
I don't think the claim is that we can really reconstruct the data. (If it is, I agree that it must be wrong). I think the claim is just that the quantum state of the matter after the black hole has evaporated contains all the information we would need to calculate the initial state. That state is of course unknowable. We can't even measure the direction of an electron's spin, so how could we measure the quantum state of the Hawking radiation emitted by a black hole?how can there be any “microreversibility” to reconstruct the data within the context of QM?
I think he's just saying that time evolution is given by exp(-iHt), which is a unitary (and therefore invertible) operator. I assume he's aware that it's not possible to measure a quantum state.Is Susskind trying to tell us for situations outside a black hole that Hawking and ’t Hooft have abandoned the HUP in favor a Super-deterministic version of BM.
Since classical and quantum mechanics both say that time-evolution is reversible, they both say that no information is lost when you throw something into the Sun. But GR says that nothing can ever leave a black hole. There isn't even any Hawking radiation in GR.That is to say toss an unopened deck of cards into the Sun and by looking at the end products of the incineration we could determine the information printed on the cards to tell if it was a Poker or UNO deck of cards?
In principle that may be true for a Classical interpretation.
But QM has an uncertainty principle that would make discovering that past information just as impossible to determine as predicting both the future location and momentum of an individual particle.
AFAIK the HUP still applies to QM, and this “paradox” being unique to black holes vs. information detail lost into the sun makes no sense.
It does, at least formally, as a mathematical limit of the black hole with the mass M->0.I don't think the idea of a zero mass black hole makes sense.
Any Cauchy surface (which includes both the exterior and the interior of the black hole) will contain ALL information about the matter that collapsed.The geometry of space-time around the black hole will contain information about the matter that collapsed, but it won't contain all of it.
But I'm saying that we don't have "right" and "wrong" in physics, and never did-- all we ever had or have is "is successfully chosen to treat this situation". That's why we still use Newton's laws far more often than Einstein's treatment in published papers on dynamics. The question is not "is quantum mechanics right", it is, "why on Earth would we ever want to put that question as if it was a meaningful absolute?" Physicists throughout history made that mistake: "assuming our current understanding is complete, we may infer..."The point if of course that if information really is lost, then QM is wrong!
That doesn't sound right to me, but I haven't been able to find an argument that proves you wrong, so maybe you're right.Any Cauchy surface (which includes both the exterior and the interior of the black hole) will contain ALL information about the matter that collapsed.
Yes, theories aren't really "right" or "wrong", they are only consistent with experiments to various degrees. Anyone who knows anything about physics knows that. But the thing is, quantum mechanics has so far been 100% consistent with all experiments. It would be a major discovery to find something that can't be described by quantum mechanics.But I'm saying that we don't have "right" and "wrong" in physics, and never did-- all we ever had or have is "is successfully chosen to treat this situation".
It isn't a mistake when these guys are doing it. It's more like assuming that the square root of 2 is rational in order to prove that it isn't. These guys are just trying to do verify that there's a contradiction between theories, and then learn something from it.The question is not "is quantum mechanics right", it is, "why on Earth would we ever want to put that question as if it was a meaningful absolute?" Physicists throughout history made that mistake: "assuming our current understanding is complete, we may infer..."
You mean all experiments for which it can be used to make a testable prediction. We are not talking about that here, this is my point. What is the test on the table here?Yes, theories aren't really "right" or "wrong", they are only consistent with experiments to various degrees. Anyone who knows anything about physics knows that. But the thing is, quantum mechanics has so far been 100% consistent with all experiments.
Thermodynamic reversibility can't be described by quantum mechanics alone. I think you mean it would be a major discovery to find something for which quantum mechanics makes a testably wrong prediction. If so, then I agree. But that in no way suggests we should use quantum mechanics to build philosophies around things we cannot even think of a practical test.It would be a major discovery to find something that can't be described by quantum mechanics.
My contention is that they are only learning something if they take their theories to be something they are not-- something other than a means for making testable predictions or ways of organizing existing data.These guys are just trying to do verify that there's a contradiction between theories, and then learn something from it.
But to examine that, we have to ask, what would have happened if the speed of light was so great that there was never an experimental way to decide between Newton and Maxwell? Of course the conclusion would have been what it actually was-- that Maxwell's theory only applies in the frame of the ether, we just don't have the experimental precision to tell what that frame is. But my way of thinking would have led instead to the conclusion that the contradiction is as irrelevant as the number of angels that can fit on a pin-- until there is a difference in a testable prediction. I'n not saying there's no point in looking for inconsistencies, I'm saying there's no point in looking for untestable inconsistencies- because consistency is only a requirement if one thinks that our theories are something more than what they are. I would say that inconsistency is only a factor to take into account when choosing the theory to apply, and I cite as evidence all the times we use Newton's laws instead of Maxwell's equations to treat electrodynamical systems of slow-moving charges.This isn't any different in principle than to study the contradiction between Maxwell's equations and Newtonian mechanics. Special relativity could have been discovered even before the Michelson-Morley experiment just by noting that there is a contradiction between the best theories of that time, and by trying to answer the question "what do we have to change to avoid the contradiction if we don't change Maxwell's equations?".
I agree that the concept of “irreversibility” appears to be so evidently true that it should be considered an important principle to find in any theory expecting to be “complete”.Now, who among us can claim the concept of "irreversibility" is not vastly effective at treating much of reality ....
Yet this concept appears nowhere in either classical or quantum mechanics. ....
..... I think irreversibility is as valuable a principle as any!"
I just don't see the value of arguments that start out "assuming quantum mechanics is a complete description...",
NO.Since classical and quantum mechanics both say that time-evolution is reversible, ...
GR says that nothing can ever leave a black hole.
There isn't even any Hawking radiation in GR.
The point is of course that if information really is lost, then QM is wrong!
But there are two issues there. The first is, if there was no HUP and classical physics worked "all the way down", would there be no irreversibility? I think you agree there would be, so the HUP cannot be the source of irreversibility if the latter would exist even without the former. The second question is, is there a form of irreversibility that is special to quantum mechanics, that does come from the HUP? I haven't seen one yet, because systems that exhibit the HUP are generally still reversible (like quantum "erasure"). To me, a good analogy is if you put cream in coffee and stir (irreversible due to turbulence), versus put cream in very thick oil and stir (nonturbulent viscosity). The latter can be reversed if the viscosity is high enough, you can "unstir the cream". Quantum mechanics, even with the HUP, tends to act more like the latter-- as long as you never couple to any classical systems that introduce noise (which returns to the cream-in-coffee analogy and is classical irreversibility).IMO "irreversibility" is an inevitable consequence, and can be directly derived from the HUP in QM.
But I'll bet that you are imagining that either or both of the "past configuration" and "current reality" are classically determined, i.e., they introduce the classical concept of irreversibility at some point or other and are not purely quantum mechanical in nature.In the same manner, QM in principle would have no expectation of being able to define a single specific past configuration necessary to establish our current reality.
Ironically, quantum mechanics in its purest form (which includes the HUP) is a perfectly predictable theory-- we can predict the wave function perfectly. We just can't predict how it will couple to classical irreversibility when we make a measurement-- but again, that's classical irreversibility, not quantum mechanical.Therefore, the reversibility of information is just as uncertain as the predictability of the future.
I can't speak to that point, I'm not knowledgeable on Susskind's argument.The argument that Susskind is promoting in his article may apply to defending such a principle in classical or GR theories, but I find the argument that the principle applies to QM as simply misguided very likely wrong and certainly not demonstrated to be more complete than CI-QM.
I did not represent that as a CI-QM position, but rather as the position that I see quite often when people talk about perceived weaknesses in CI-QM. Indeed, I think CI-QM is at times itself a bit over-interpreted, but less so than most of the rest.As to those that begin by "assuming quantum mechanics is a complete description..."
That misrepresents what Niels Bohr said and meant by CI-QM.
I agree that there is no more complete interpretation, because "more complete" to me means "is able to understand more observations". But as I said, I don't think the uncertainty principle controls irreversibility because it does not mediate the destruction of information, it mediates the existence of information in the first place. It is the classical couplings we use in our science that do the destroying, and that is classical irreversibility.IMO no one has established a more complete interpretation of QM, which would eliminate the uncertainty principle to allow the reversible reconstruction of destroyed information.
Sorry I cannot get past your first two sentences so the rest is of no help. You appear to be contradicting yourself. If I follow you negatives correctly I would agree that in “all the way down classical physics" there would ‘be no irreversibility’.But there are two issues there. The first is, if there was no HUP and classical physics worked "all the way down", would there be no irreversibility? I think you agree there would be, so the HUP cannot be the source of irreversibility if the latter would exist even without the former.
Oh, that surprises me-- I thought you recognized that irreversibility was also a classical concept. Indeed, it's usefulness as a principle greatly precedes quantum mechanics. Are you saying you think that heat doesn't flow from cold to hot because of the HUP? If so, why did it not surprise Lord Kelvin-- he didn't know quantum mechanics.If I follow you negatives correctly I would agree that in “all the way down classical physics" there would ‘be no irreversibility’.
What do you mean by ATWD?Meaning YES reversibility is expected to allow reconstructing the original conditions that created our current condition in a supposed ATWD Classical view.
Those were all pretty absurd over-interpretations of classical mechanics. There was zero evidence for any of them, and scads of contrary evidence, long before quantum mechanics. Are you saying the patent office should have been considering perpetual motion machines right up until quantum mechanics was developed? Why was it called the second "law" of thermodynamics, if it flew in the face of classical physics?Including recovering lost information.
Goes along with Classical predetermination, preordained future and lack of free will.
But actually, the HUP leads to no new irreversibility problems that were not already there. You never encounter any irreversibility stemming from the HUP unless a classical system is involved somehow. Unless you know of a counterexample that I don't.MY point still is, that in comparison to that the HUP is the theoretical source for an irreversibility principle, NOT ATWD Classical or GR for that matter.
Yes, my thinking we'd agree on that first part made the second part hard to discuss!Relook at your logic and see if I’ve misread your opening comments somehow.
Don’t see how the rest can mean anything if we are not clear on this.
It is the version of Classical I thought you were discussing.What do you mean by ATWD?
But ATWD, that you brought up, is a version of Classical and the only one I can see that Hawking Susskind et.al. can be thinking of to claim “information should not be lost”. And I can think of no interpretation of QM that would indicate “information should not be lost”, if you know of one let me know.Those were all pretty absurd over-interpretations of classical mechanics.