Do Black Holes Destroy Information?

  • #1
Stephen Hawking proposed that black holes will eventually evaporate due to Hawking radiation, thus all information eaten by the black hole is destroyed. This violates basic physics, and hawking soon recanted his views, but there is still no real answer to whether they do or don't destroy information, from what I've seen. Do physicists still debate whether they do or don't, or has the debate shifted to which theory explaining why information is not lost is correct?
 

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  • #2
PeterDonis
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Do physicists still debate whether they do or don't, or has the debate shifted to which theory explaining why information is not lost is correct?
I think it depends on which physicists you talk to. :wink:
 
  • #4
atyy
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  • #5
Demystifier
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Do physicists still debate whether they do or don't, or has the debate shifted to which theory explaining why information is not lost is correct?
Most assume that information is not lost and try to understand how, but some still debate whether it is lost or not.
 
  • #6
.Scott
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Stephen Hawking proposed that black holes will eventually evaporate due to Hawking radiation, thus all information eaten by the black hole is destroyed.
Since the Hawking radiation can be emitted in more than one way (many more than one way), the Hawking radiation contains information.

When information is said to be preserved in QM, it is referring to the amount of information - for example, as measured in bits. So if information is preserved in a black hole, then the number of bits it would have taken to describe the material that formed the black hole should be precisely the same number of bits it would take to describe the resulting Hawking radiation.

It would be very interesting if it could ever be determined that these values were not equal. For one thing, it would imply one or more of the following: that information can be fed into our universe from "somewhere else", or that there is an inherent QM direction to time (indicated by a monotonic reduction of information), or that there is something fundamental that keeps us from tallying up information in this way (perhaps because there are redundant copies of the information).
 
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  • #7
Boing3000
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When information is said to be preserved in QM, it is referring to the amount of information - for example, as measured in bits.
Is there any good reference which explains how many bits is needed to store the spin of a particle ? To me this kind of imply that there are hidden variables to be "encoded", and those variable are discreet (which seems unlikely for a spin angle))
 
  • #8
Since the Hawking radiation can be emitted in more than one way (many more than one way), the Hawking radiation contains information.

When information is said to be preserved in QM, it is referring to the amount of information - for example, as measured in bits. So if information is preserved in a black hole, then the number of bits it would have taken to describe the material that formed the black hole should be precisely the same number of bits it would take to describe the resulting Hawking radiation.

It would be very interesting if it could ever be determined that these values were not equal. For one thing, it would imply one or more of the following: that information can be fed into our universe from "somewhere else", or that there is an inherent QM direction to time (indicated by a monotonic reduction of information), or that there is something fundamental that keeps us from tallying up information in this way (perhaps because there are redundant copies of the information).
Didn't hawking himself say there is no connection between in ingoing particles and the outgoing radiation?
 
  • #9
Same Q as #8 with added query:
Is there any reason to assume an closed system interaction with a black hole violates any conserved quantity... angular momentum, mass-energy, charge, color charge etc.? If not what goes "missing" or how is any information literally "destroyed"?
 
  • #10
.Scott
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Didn't hawking himself say there is no connection between in ingoing particles and the outgoing radiation?
Possibly - but not to my knowledge.
There is certainly a connection. If it weren't for the incoming particles, there would be no black hole to begin with.
As @Demystifier said, most are looking for the connection. There are real theoretical problems with allowing information to be created and destroyed.
 
  • #11
Strilanc
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Is there any good reference which explains how many bits is needed to store the spin of a particle ? To me this kind of imply that there are hidden variables to be "encoded", and those variable are discreet (which seems unlikely for a spin angle))
The spin of a spin-half particle is capable of storing (or being represented by) exactly one qubit.
 
  • #12
Boing3000
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The spin of a spin-half particle is capable of storing (or being represented by) exactly one qubit.
My issue is about the usage of the term "information" or "bits", not Qubit.
I am under the impression that one would need an infinite number of bit to store a Qubit
 
  • #13
Strilanc
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My issue is about the usage of the term "information" or "bits", not Qubit.
I am under the impression that one would need an infinite number of bit to store a Qubit
When people talk about "conservation of information", especially with respect to black holes, they always mean quantum information i.e. qubits.

Also, it's not correct to say that a qubit requires infinite bits to store.
 
  • #14
Demystifier
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When people talk about "conservation of information", especially with respect to black holes, they always mean quantum information i.e. qubits.
Not exactly. They mean the conservation of quantum entropy (von Neumann entropy), and this entropy is not measured in qubits.
 
  • #15
Strilanc
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Not exactly. They mean the conservation of quantum entropy (von Neumann entropy), and this entropy is not measured in qubits.
Hmmm, yes that's probably a better way to put it.
 
  • #16
TeethWhitener
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The question is unresolved. There has been recent research based on Hawking's paper and the https://arxiv.org/abs/1207.3123.
What ever happened with Hawking’s big announcement? It’s way beyond my ability to understand, but I (like to pretend that I) kind of got the gist of John Baez’s explanation:
http://math.ucr.edu/home/baez/week207.html

As far as I understand it, to examine the question of information loss, he computes the path integral over all (relevant?) metrics and argues that the contribution from nontrivial (I.e., black hole) topologies goes to zero in the far future limit. Coupled with the fact that non-black hole metrics clearly have no problem with unitarity, the total time evolution remains unitary. Caveat—I might be totally off in my explanation.

Baez describes several technical points that I don’t really understand. My question is: has anyone pursued Hawking’s initial idea further (alternately: has anyone shown that it’s likely infeasible)?
 
  • #17
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interesting topic, pardon my ignorance if this is the case but if all that we know about BH is true then how come they can possibly preserve all of the information regarding an incoming piece of matter given the processes that happen inside (supposedly) , isn't that the same as throwing a rare piece of furniture in a fire and then trying to recover the information about it's color and shape simply by analyzing the ash and gaseous emissions from the fire but all they could tell is roughly the kind of wood was burned and chemicals not the shape or color or other distinctive features of the object?



We now know the elements that make up stars also the ones which are big enough that after their fuel depletes turn into black holes, but what if all the stars in the past universe were big enough to become black holes and we came after they all had turned into black holes (for the sake of the argument pretend we can live without "sunlight") could we simply by using hawking radiation determine the exact chemical structure of the star that made the BH at the moment it turned into one by gathering all the emitted radiation or portions of it?
 
  • #18
PeterDonis
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could we simply by using hawking radiation determine the exact chemical structure of the star that made the BH at the moment it turned into one by gathering all the emitted radiation or portions of it?
That is the question of black hole information loss--do black holes destroy information? We don't know the answer.
 

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