Why is the BH Information Paradox Called a Paradox?

[Grinkle]

TL;DR

Isn't this 'just' one of multiple places in nature where QM theory and Relativity theory don't synch up?

We don't have a quantum theory of gravity. To my B level thinking, losing information at the EH of a black hole is just one of multiple known places where QM meets relativity and it becomes clear that our understanding is incomplete. I don't see it as any different than making the same statement to discuss what is meant by the singularity (the singularity is where we just don't know).

I may be just overly-impressioned by the popular science videos I watch, but my perception is that discussions around information loss at the EH are much more dramatic and concerning to physicists than discussions about us not knowing how to model what we call the singularity.

I've never heard "the singularity paradox" or the "the collapse paradox" or etc etc to describe the existence of BH's, we are instead content to name the unknown part "singularity" and proceed from there - is the information paradox fundamentally more puzzling or surprising for some reason? There are probably some consequences of information actually being destroyed that I don't understand. To my thinking, it implies that the wave equation would not be a valid model for all conditions in nature, and such statements are not usually a big concern to scientists who are quite used to finding out that contemporary theory has less than universal applicability.

 

[DaveC426913]

There's a lot of material out there on the specific of the BHIP, have you read the specifics?

Wiki has a simplistic primer that at least introduces the nature of the paradox:

"Hawking also argued that the details of the radiation would be independent of the initial state of the black hole...

[but that]

...violates a core precept of both classical and quantum physics—that, in principle, the state of a system at one point in time should determine its value at any other time.[3][4] Specifically, in quantum mechanics the state of the system is encoded by its wave function. The evolution of the wave function is determined by a unitary operator, and unitarity implies that the wave function at any instant of time can be used to determine the wave function either in the past or the future."

https://en.wikipedia.org/wiki/Black_hole_information_paradox

Hopefully, it will lead to more fruitful reading.

 

[Grinkle]

@DaveC426913

I get that, at least I think I do. What I don't get is why (if indeed it is, maybe my perception is skewed) finding a condition in nature where this doesn't appear to be the case is so specifically concerning. That is how science goes. Its not a paradox, its business as usual - we need a more complete theory. But we already know that our most advanced theories are incomplete and we knew this even before the potential for information loss was known. It isn't as though we had our GUT and then suddenly along came information loss to torpedo it.

 

[DaveC426913]

I guess the point is: this isn't a case of 'we don't have enough information to know how this works' - it's a case of 'we have plenty of information encapsulated in two different, well-established theories - but they produce incompatible results' - which is pretty much the definition of a paradox.

 

[Grinkle]

Thanks, @DaveC426913 - I agree that is a difference.

 

[PAllen]

I will link a paper arguing that basically there is no paradox. At one point, I thought such an argument was borderline crank, but here it is made by two very esteemed physicists (I have been meaning to open a thread on this paper, but haven’t digested enough of the details to want to do that yet):
https://arxiv.org/abs/1703.02140

 

[phinds]

https://www.amazon.com/dp/0316016411/?tag=pfamazon01-20

 

[PeterDonis]

losing information at the EH

That's not where the supposed "information loss" in a black hole occurs. It occurs at the singularity. Some proposed solutions to the information loss problem rely on observers outside the horizon not being able to receive information from inside the horizon, but that's not the same as the information loss occurring at the horizon.

From a quantum point of view, the problem with information loss is violation of unitarity, but unitarity is not violated at the horizon. It's only violated at the singularity.

I may be just overly-impressioned by the popular science videos I watch

Whether you are or not, the real issue I see is that you are not giving any references at all in this thread. As @DaveC426913 has said, there is a lot of information out there. You need to reference at least some of it as a basis for discussion. A discussion based on vague generalities with no references to back anything up is not going to go anywhere useful.

 

[Demystifier]

Summary:: Isn't this 'just' one of multiple places in nature where QM theory and Relativity theory don't synch up?

We don't have a quantum theory of gravity. To my B level thinking, losing information at the EH of a black hole is just one of multiple known places where QM meets relativity and it becomes clear that our understanding is incomplete. I don't see it as any different than making the same statement to discuss what is meant by the singularity (the singularity is where we just don't know).

It's not that we don't have a quantum theory of gravity at all. We have some incomplete theories of quantum gravity. We have some rough idea how quantum gravity should work, even if we don't have all the details. But the apparent loss of information does not look like a detail. Any attempt to resolve the apparent loss of information seems to imply a dramatic consequence, suggesting a radical change of something that we thought we understood at least qualitatively. That's why it's called paradox, because it seems that resolution requires to abandon some of the basic principles that we thought we understood.

There are probably some consequences of information actually being destroyed that I don't understand.

Yes. All quantum theories we understand well conserve information. All candidate quantum gravity theories (string theory, loop quantum gravity, ...) seem to conserve information. And yet, it looks as if black holes don't conserve information, or if they do, we don't know how.