What is the Information Loss Paradox and How Does Hawking Radiation Relate?

[spidey]

can someone explain information loss paradox in layman terms without using any quantum physics terms...i read in some sites but i couldn't understand as they are explaining using some jargon terms...

 

[Fredrik]

General relativity says that black holes are kind of like enormous elementary particles. A black hole has a mass, a total electric charge, an angular momentum, and no other properties whatsoever. If that's true, then all the information about anything that falls into a black hole is gone forever.

Quantum mechanics on the other hand says that if you know the initial state, you can calculate the final state, and vice versa. So if everything is described by quantum mechanics, this must hold even if the matter described by the initial state collapses to a black hole.

That's the paradox. GR says the information is gone. QM says it isn't.

A black hole will eventually evaporate through a process called Hawking radiation. The black hole will lose mass by emitting radiation until it's gone. The radiation is the final state of the matter that collapsed to the black hole or later fell into it. So if QM is correct, then the radiation must somehow contain all the information that's needed to reconstruct the initial state. (E.g. if you throw your hard drive into a black hole, all the information about the pornography you downloaded is present in the radiation). That would be pretty surprising, because we're talking about a kind of thermal radiation, a lot like the infrared radiation you can feel from a hot stove. That kind of radiation is normally completely random, but if QM is correct, the quantum states of particles in the radiation from the black hole must somehow be correlated so that the information is present in the correlations.

(Correlations in the Hawking radiation is not the only resolution of the paradox that has been proposed. It's just the one that's the easiest to understand).

Scientific American article by Leonard Susskind: http://staff.science.uva.nl/~jdeboer/gr/susskind.pdf

 

[spidey]

Thank you Fredrik for your clear explanation...I have one doubt...the only difference between black hole and other other heavenly bodies like earth,moon is the heavy gravitational field...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 definitely on the moon's surface...likewise the same hard drive should be on the black hole's surface,isn't it? then how GR says information is lost ...information is on the black hole's surface,am i right?only difference is that hard drive can't 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..

 

[Demystifier]

GR says the information is gone.

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. )

Now let me try to explain the information paradox in simple terms by myself.
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.

Now, what is the solution of the paradox? To be clear, there are many proposals and there is no consensus among experts. In my opinion, the solution is that the particles that fall into the black hole are virtual (not real), so the information carried by them is not physical. For the details see
http://xxx.lanl.gov/abs/0708.0729 [Eur. Phys. J. C 54 (2008) 319]

 

[RandallB]

From the Leonard Susskind article:

… the principle of microreversibility, which has always held in classical and quantum physics, …

Since when is this true?
QM and classical are not the same thing! (edit; in regard to microreversibility)
If a deck of cards are randomly shuffled to the point of taking advantage of the HUP within QM then how can there be any “microreversibility” to reconstruct the data within the context of QM?
If we are to take the HUP as serious and correct part of QM that denies that the classical as ever being able to produce a complete explanation of reality; how are we to expect QM to apply microreversibility without accounting for the principle contained in HUP.

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.
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.

 

[friend]

Now, what is the solution of the paradox? To be clear, there are many proposals and there is no consensus among experts.

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.

 

[Ken G]

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.

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!"

So I agree with RandallB that I don't see "what's the big deal" with information loss in black hole physics, but I don't distinguish quantum or classical mechanics in that regard-- they are all snippets of our descriptions of reality that simply don't describe everything we need to understand about our universe. I just don't see the value of arguments that start out "assuming quantum mechanics is a complete description...", any more than a physicist in 1900 was making any sense when they said "assuming Newton's laws give a complete description...". This isn't what physics is for, it's not a "philosophy engine", it's a way to predict systems-- and the fingerprints of the physicist are all over the result in the axiomatic structure chosen.

 

[Fredrik]

the only difference between black hole and other other heavenly bodies like earth,moon is the heavy gravitational field...

Actually, almost the opposite is true. The gravitational field is about the only thing a black hole has in common with a star.

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 definitely on the moon's surface...likewise the same hard drive should be on the black hole's surface,isn't it?

A black hole doesn't have a surface.

then how GR says information is lost ...information is on the black hole's surface,am i right?only difference is that hard drive can't 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 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.

Also, GR doesn't say anything about Hawking radiation. According to GR a black hole will stick around forever, and can only get bigger, not smaller. So GR definitely says that the information is gone. Hawking radiation is a prediction of another theory, quantum field theory in curved space-time, which is a partial union of quantum mechanics and GR. That prediction doesn't solve the problem, it merely suggests a possible way out: correlations in the Hawking radiation. If the information is contained in the Hawking radiation, we still have to explain how it got there. One mechanism that has been suggested is quantum teleportation.

 

[Fredrik]

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.

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.

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.

I don't think the idea of a zero mass black hole makes sense.

 

[Fredrik]

From the Leonard Susskind article: Since when is this true?
QM and classical are not the same thing!

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.

how can there be any “microreversibility” to reconstruct the data within the context of QM?

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?

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.

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.

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.

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.

 

[Fredrik]

I just don't see the value of arguments that start out "assuming quantum mechanics is a complete description...",

The point if of course that if information really is lost, then QM is wrong!

 

[Demystifier]

I don't think the idea of a zero mass black hole makes sense.

It does, at least formally, as a mathematical limit of the black hole with the mass M->0.
See, e.g., the discussion around Eq. (3) in
http://xxx.lanl.gov/abs/hep-th/0402145 [Int.J.Mod.Phys. D14 (2005) 2257]

 

[spidey]

If we say information is lost in black hole since it is not in our world, which would also mean black hole is also lost from our world... I personally believe that information is not lost..we say a thing is lost only if
1. we can't get it back
2. we don't know the location
In this case, we know the location which is the black hole then why we say information is lost and have to worry about it...I think there is no problem.. we are creating an imaginary problem and trying to solve it...a paradox arises if a theory gives unbelievable results and also contradictory to reality...either theory should be wrong or paradox should be wrong...

 

[Demystifier]

In this case, we know the location which is the black hole then why we say information is lost and have to worry about it...

You missed the point. The black hole evaporates, so at the end there is no black hole in which information could be located.

 

[Demystifier]

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.

Any Cauchy surface (which includes both the exterior and the interior of the black hole) will contain ALL information about the matter that collapsed.

 

[Ken G]

The point if of course that if information really is lost, then QM is wrong!

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..."

Using theory to try and decide if information is lost in black holes is mistaking physics for a "philosophy engine". Make a testable prediction.

 

[Fredrik]

Any Cauchy surface (which includes both the exterior and the interior of the black hole) will contain ALL information about the matter that collapsed.

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.

Anyway, I've been reading the Wikipedia article and parts of the references in it, and it seems that even if I was right when I said that "GR says the information is gone" (and I may not have been), that isn't what the experts have in mind when they talk about the information paradox. The paradox is that when a black hole has evaporated completely, the final state doesn't contain all the information we would need to calculate the initial state.

 

[Fredrik]

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".

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.

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..."

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.

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?".

 

[Ken G]

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.

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?

It would be a major discovery to find something that can't be described by quantum mechanics.

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.

These guys are just trying to do verify that there's a contradiction between theories, and then learn something from it.

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.

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?".

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.

 

[RandallB]

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...",

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”.

But I disagree that the idea appears nowhere in quantum mechanics.
IMO "irreversibility" is an inevitable consequence, and can be directly derived from the HUP in QM.
Just as it defines our inability to specifically predict both the future location and momentum of an individual particle, the HUP tells us we cannot predict with certainty future events or information.
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. It seems to me that in principle QM uncertainty cuts both ways; no predetermined future from our current state, and our current state cannot be considered preordained from a deterministic past. Therefore, the reversibility of information is just as uncertain as the predictability of the future.

As theories go, both Classical and General Relativity might allow for such a deterministic view in principle within their theories, but neither have resolve the simultaneous prediction of both location and momentum for an individual particle and only some views of GR (such as Hawking QFT in curved space-time) allow Blackholes to “evaporate”. 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. At least to the extent that CI-QM has not been convincing Wrong in the

As to those that begin by "assuming quantum mechanics is a complete description..."
That misrepresents what Niels Bohr said and meant by CI-QM. His point was that QM was as complete as is possible, and that no other description (such as Einstein expected) could ever be more complete. 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.

Although I personally do not think QM is complete, uncertainty and "irreversibility" of information loss are principles I believe will survive a more complete theory that might replace it someday. But that’s a personal opinion, probably based on my belief in free will.

 

[RandallB]

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!

NO.
Quite the opposite, my point was if you take QM as correct including HUP then information must be able to be "irreversibility" lost. And to recover it in the examples given would be a demonstration that QM was incomplete.
IMO the HUP prevents a reversible time evolution.

Also, Hawking radiation is a GR interpretation that uses QFT as well, so that is at least one GR version that does not say “nothing can ever leave a black hole”.

 

[Ken G]

IMO "irreversibility" is an inevitable consequence, and can be directly derived from the HUP in QM.

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).

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.

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.

Therefore, the reversibility of information is just as uncertain as the predictability of the future.

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.

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 can't speak to that point, I'm not knowledgeable on Susskind's argument.

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 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.

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.

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.

 

[RandallB]

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.

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’.
As in irreversibility NOT a principle of ATWD Classical.
Meaning YES reversibility is expected to allow reconstructing the original conditions that created our current condition in a supposed ATWD Classical view. Including recovering lost information.
Goes along with Classical predetermination, preordained future and lack of free will.

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.

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.

 

[Ken G]

If I follow you negatives correctly I would agree that in “all the way down classical physics" there would ‘be no irreversibility’.

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.

Meaning YES reversibility is expected to allow reconstructing the original conditions that created our current condition in a supposed ATWD Classical view.

What do you mean by ATWD?

Including recovering lost information.
Goes along with Classical predetermination, preordained future and lack of free will.

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?

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.

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.

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.

Yes, my thinking we'd agree on that first part made the second part hard to discuss!

 

[RandallB]

What do you mean by ATWD?

It is the version of Classical I thought you were discussing.
You said (All The Way Down) didn’t you – just shorten it to ATWD Classical.
Do you remember what that is – the billiard ball example where with perfect knowledge ATWD to the finest detail of the movement of several balls on the table you should be able to calculate backwards to their original paths and interactions until you get down to a single ball rolling away free from the other stationary balls. That one obviously the ball hit by the cue.

Good point about thermodynamics, but that is a different interpretation of Classical than ATWD Classical. You cannot make a meaningful agreement by using two different theory versions without making clear the difference between them and when you are applying which version.

Rather than argue against someone that you agree with make your point clear.

Those were all pretty absurd over-interpretations of classical mechanics.

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.

If as you say it is not a matter of an interpretation being “ right or wrong in physics” I would certainly consider it a incorrect application of HUP. My point remains; there is no QM justification for expecting “information should not be lost”. (ref. HUP)

The point you should be making is that ATWD Classical thinking that “information should not be lost” is just as absurd an idea to hang on Classical. And based on the well accepted Thermodynamics Interpretation of Classical there is no Classical reason for expecting “information should not be lost” either. (I.E. ATWD Classical is incorrect if not 'wrong')

I can see where QM-HUP can lead to Thermodynamics; I’m not so sure thermodynamics could lead to the overall principal of HUP. Which of the two is more complete would a different discussion but yes obviously Thermodynamics was discovered first.

 

[Ken G]

It is the version of Classical I thought you were discussing.
You said (All The Way Down) didn’t you – just shorten it to ATWD Classical.

Oh I see, gotcha.

Do you remember what that is – the billiard ball example where with perfect knowledge ATWD to the finest detail of the movement of several balls on the table you should be able to calculate backwards to their original paths and interactions until you get down to a single ball rolling away free from the other stationary balls.

Actually, I would argue that this is something added to ATWD Classical. The latter only says you can map input uncertainties into prediction uncertainties, and invert them too. It never says you can recover the initial state, precision limitations and Lyapunov exponents being what they are. You might way "I mean in principle", but I'm talking about a principle too-- the principle of practicality in science, that what cannot be tested is not scientific. This is quite relevant to the discussion at hand-- when insurmountable practical limitations surface, those limitations are ingrained in science too.

Good point about thermodynamics, but that is a different interpretation of Classical than ATWD Classical. You cannot make a meaningful agreement by using two different theory versions without making clear the difference between them and when you are applying which version.

Right-- ATWD Classical, like the rest of physics, is a collection of axioms we invoke whenever we decide we need them. It is not intended to be a complete description of reality, and why people thought it was just indicates to me they were confused about what science was-- and still is.

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”.

I think they were talking about the time reversibility of every dynamical equation they view as fundamental in the physics they were doing. That was inconsistent with the boundary value problem applied to a black hole solution. So we have a set of dynamical equations that are not consistent with a boundary-value problem. So what? We just pick what we want in every situation-- when will we stop imagining that physics is different than what it has always been?

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.

I point to the invertibility of unitary time-evolution operators. Why does that not make quantum mechanics information-preserving?

Perhaps you are using a different meaning for information, that expressly involves coupling to classical systems to "extract" said information. That is not information preserving if you only count the information it gives us access to, but that was not the meaning of "information" as described in this thread.

If as you say it is not a matter of an interpretation being “ right or wrong in physics” I would certainly consider it a incorrect application of HUP. My point remains; there is no QM justification for expecting “information should not be lost”. (ref. HUP)

The HUP is a constraint on the information that is present, not on what survives extraction. The latter would get us into "collapse of the wavefunction" issues that have nothing to do with the HUP and would further muddy the water.

The point you should be making is that ATWD Classical thinking that “information should not be lost” is just as absurd an idea to hang on Classical.

That would be a confusing point to make, because although I agree it is also absurd, it is absurd for different reasons. The information loss you refer to is actually something that is "lost in translation" from the quantum to the classical realm (again getting into wavefunction collapse issues). That is not the same as the way information is "lost" in the purely classical realm-- which is a practical matter having to do with what we are actually capable of tracking with any given experimental apparatus (which might be very similar to the wavefunction collapse issues, but again is not the meaning of information being used here).

And based on the well accepted Thermodynamics Interpretation of Classical there is no Classical reason for expecting “information should not be lost” either. (I.E. ATWD Classical is incorrect if not 'wrong')

Physics theories are not "wrong", as I said, they are "not accurate enough" or "incapable of addressing the question I am interested in". In your way of thinking, the vast majority of all published papers in physics are "wrong". That is a curious interpretation of the meaning of that word. It has formal validity, but science has never been a formal undertaking-- even when it sets up axiomatic structures, it chooses from among them in a nonformal way.

I can see where QM-HUP can lead to Thermodynamics; I’m not so sure thermodynamics could lead to the overall principal of HUP.

The two do not "talk" to each other in that manner. Neither can be used to derive the other, they each stem from their own separate axioms. The HUP comes entirely from the Schrödinger equation (does it not?), and that equation describes perfectly time-reversible behavior.

 

[masudr]

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.

Why not? For a given $T_{ab}$ there is a unique $G_{ab} = R_{ab}-\frac{1}{2}Rg_{ab}$.

 

[RandallB]

Oh I see, gotcha.
Actually, I would argue that this is something added to ATWD Classical. The latter only says ...

IMO the “all the way down” version implies super-determinism and I take that and the ATWD expectation both to be Wrong.
However if you insist that:

Physics theories are not "wrong", as I said, they are "not accurate enough" or "incapable of addressing the question I am interested in".
In your way of thinking, the vast majority of all published papers in physics are "wrong".

I take “Wrong” as an opinion that can vary based on the evidence and who is convinced by it.
For example I’m a Local Realist which means the majority of science considers my belief that there is a more complete explanation to reality than QM can provide as “Wrong”. I’m accept being considered wrong, as that can change. I guess I just don’t see the point in splitting hairs over a formal definition.
For example I think it is clear that QM & GR are fundamentally incompatible in principle and they both cannot be Right, therefore something must be wrong. I’m more interested in figuring out what is wrong, to get to a more correct solution than worring about how the word 'wrong' is used.

I point to the invertibility of unitary time-evolution operators. …
The HUP comes entirely from the Schrödinger equation (does it not?), and that equation describes perfectly time-reversible behavior.

I know next to nothing about “unitary time-evolution operators”, do people believe it overcomes the uncertainty principle included in HUP?
My understanding was that historically HUP came first and Schrödinger was shown to be equivalent to it.
If "perfectly time-reversible" can mean super-determinism I'd consider it wrong, but I suspect HUP is still contanined within Schrödinger.

 

[Ken G]

IMO the “all the way down” version implies super-determinism and I take that and the ATWD expectation both to be Wrong.

The theory is built to be super-deterministic-- this "implies" nothing! That's my whole point, we keep mistaking the axioms we choose to accomplish various things as though they told us something fundamentally true about reality. Why do we do that? To me it is an obvious over-extrapolation of what science is. Yet we do it so automatically I often have trouble making people see that this is at best not necessary to science, and at worst it is unscientific.

For example I’m a Local Realist which means the majority of science considers my belief that there is a more complete explanation to reality than QM can provide as “Wrong”.

Why do people think that their personal philosophy is relevant to science? This gets back to what I was saying above, it's just a mistaken idea of what science is. It isn't a philosophy engine-- you are welcome to be any kind of "ist" that lights your fire. If anyone tells you that you are "wrong", they've already removed their scientist hat and put on their own "ist" hat. But if they challenge you to show that your philosophies have any scientific merit, then they are still being scientists.

For example I think it is clear that QM & GR are fundamentally incompatible in principle and they both cannot be Right, therefore something must be wrong.

But that's just what I'm talking about, I don't see that as scientific language. Something is incomplete, yes, but we are always foolish to expect otherwise, in every case. Newton's laws (with the implied Galilean relativity) makes less accurate predictions than Einstein's relativity, so I guess you would say it is "wrong", but it gets used far more often in physics publications (especially astrophysics) than does Einstein's. Why are so many papers "wrong", and how do they get past the referees?

I’m more interested in figuring out what is wrong, to get to a more correct solution than worring about how the wrod 'wrong' is used.

You can't do one without the other, or you can't referee all those papers.

I know next to nothing about “unitary time-evolution operators”, do people believe it overcomes the uncertainty principle included in HUP?

It doesn't "overcome" the HUP, it explains what it is. But one doesn't need the mathematical formalism, just think about water waves. Water waves demonstrate a principle very analogous to the HUP-- if you try to limit the width of the "throat" they pass through, they spread out (constraints on the position of the source implies lack of constraints on the spread angle of propagation). That's a property of waves, of their reliance on interference to determine how they propagate. Is a water wave irreversible? Watch what happens when you dip your finger in the exact center of a coffee cup.

If "perfectly time-reversible" can mean super-determinism I'd consider it wrong, but I suspect HUP is still contanined within Schrödinger.

Time reversibility is different from super-determinism, but it would seem to have a lot to do with information conservation.

 

[RandallB]

Why do people think that their personal philosophy is relevant to science?
But if they challenge you to show that your philosophies have any scientific merit, then they are still being scientists.

Why are so many papers "wrong", and how do they get past the referees?

But that is why different philosophies are directly relevant to science.
Where else do new concepts about the fundamental nature of reality come from but from differing views or “scientific religions” (small “r” as distinct from large “R” of theological or spiritual “Religions”).

“get past the referees”
– It is not the job of referees to decide if the philosophic belief that might be contained within an idea; it is actually a problem that they often do reject scientific doctrine not in line with their own even if the ideas in the papaer may be workable.
Their job is to evaluate if the ideas might be useful and are clear and logical enough that others can evaluate them (pro or con) in scientifically productive ways.
They are not intended to sit in judgement.
And papers shouldn’t be considered Right or even Accurate because they are published, only useful.

For example there are several models proposed for an atom (cubic, plum-pudding, Saturnian, Rutherford, Bohr) using any of those is not a disqualification for a paper; Only that the ideas and how they are used may actually be useful in the context of the paper.
For example, Bohr circular orbits in the Bohr Atom is well understood to be wrong and an incorrect description of atomic structure. But even modern papers still use Bohr circular orbits as an analogy of reality that accurately helps describe fundamental elements of nature such as the fine structure constant.

I don’t think the current scientific consensus that these atomic models are ‘wrong’ yet some remain useful as scientific analogies of reality, will ever change to declare one of them as a correct and complete description of atomic structure.

In the same way I believe QM will always serve as an accurate analogy of reality but someday we will be able to demonstrate that QM and Bohr as wrong to consider it a complete description of reality.

Is a water wave irreversible? Watch what happens when you dip your finger in the exact center of a coffee cup.

Time reversibility is different from super-determinism, but it would seem to have a lot to do with information conservation.

But it does not explain what HUP is, it only gives an analogy of it. And the water wave is not reversable, regardless of appearence. Sure you can even remove your finger with perfect timing so as to make the water ‘feel’ it returned the energy that first created the waves to attempt to leave the water perfectly flat as if the finger never touched the water. But an incorrect analogy of nature because it is incomplete; a detailed snapshot of a little wave approaching your finger will show it does not reconstruct and conserve the information contained in the snapshot taken of the apparently identical looking wave departing your finger a moment ago. Individual particles of water and items of fluff floating on the water are rearranged as dispersion has moved them to new locations.
This like many other examples support HUP & the one way direction of thermodynamic entropy, and tells me that “information conservation” should not be considered a requirement of reality.

And IMO HUP defines QM as not requiring information conservation. To the extent that some issue refereed papers stating otherwise; I’ve not seen any give satisfactory detail on how information is conserved from the past anywhere in nature, without nature propagating a Super-deterministic future. HUP says no to both.