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B Black Holes and Information

  1. Dec 21, 2016 #1
    What happens to the information about the objects falling into the black hole? Are their states somehow contained in the Hawking Radiation, and if so, how? Or is the information scrambled as it passes the EH?
     
  2. jcsd
  3. Dec 22, 2016 #2

    mfb

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    That is one of the big open questions about black holes. See No-hair theorem for an introduction.
     
  4. Dec 23, 2016 #3
    ok, thanks
     
  5. Dec 23, 2016 #4

    Chronos

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    Nature abhors waste. Whatever goes in comes out, irrespective of how mangled it may become.
     
  6. Dec 26, 2016 #5
    Dear Chronos.
    Great answers but I don't understand your final answer.
    I was under the impression that anything crossing the event horizon of a black hole was lost to our universe forever.
    Is that no longer currently accepted theory?
     
  7. Dec 26, 2016 #6

    mfb

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    It is unknown.
     
  8. Dec 30, 2016 #7

    phinds

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    Suskind and Hawking had a 30 year running battle about exactly that. Suskind said that information about the stuff going in a black hole could not be lost and Hawking said it had to be. Suskind won and wrote a book about it.

    https://www.amazon.com/Black-Hole-War-Stephen-Mechanics/dp/0316016411

    Overview
    Hawking proposed that information is lost in black holes, and not preserved in Hawking radiation.[2] Susskind disagreed, arguing that Hawking's conclusions violated one of the most basic scientific laws of the universe, the conservation of information. As Susskind depicts in his book, The Black Hole War was a "genuine scientific controversy" between scientists favoring an emphasis on the principles of relativity against those in favor of quantum mechanics.[1] The debate led to the holographic principle, proposed by Gerard 't Hooft and refined by Susskind, which suggested that the information is in fact preserved, stored on the boundary of a system.[3]
     
    Last edited by a moderator: May 8, 2017
  9. Dec 31, 2016 #8

    Chronos

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    There are any number of ways quantum information could eventually be liberated by the time a black hole evaporates. I see no need resort to quantum mechanics to forbid quantum information from surviving indefinitely.
     
  10. Jan 3, 2017 #9
    What's beyond the "Event Horizon" of a Black Hole?
     
  11. Feb 6, 2017 #10
    I've wondered about this. If an organism fell into a black hole, presuming they didn't burn up en route, I can see how the information regarding the organism's atoms might be preserved. However, wouldn't the information pertaining to the conditioned processes of life be lost, as seems to occur with any death?

    Sorry if it's a dumb question.
     
  12. Feb 6, 2017 #11
  13. Feb 6, 2017 #12

    mfb

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    Every object gets destroyed - that is sure.

    The question about information loss is different. Let a nuclear weapon explode next to some object: the object gets completely destroyed. The information survives: if you could track all atoms after the explosion and extrapolate back, you could figure out how the object looked before the explosion. In theory - there is no way to actually do this.
     
  14. Feb 7, 2017 #13
    Thaks for your reply.

    So basically the information about atoms' prior spin, location and type is contained within the chaotic information store that is in the BH's event horizon and a more advanced species could theoretically recreate all the things that fell in? So, on a practical basis, the quality of the information is not preserved, but the quantity is.

    Would a black hole's absorption of a complex object add more to its mass and generate more heat than an equally massive simple object?
     
  15. Feb 7, 2017 #14

    BillTre

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    I have thought about this scenario for the same reason: could larger scale information be lost?

    I am not trained in quantum mechanics, so perhaps I'm missing something, but:

    It seems to me that something blown up in a nuclear explosion would be destroyed by (among other things) by interacting with many particles and photons.
    Each photon and particle would exist in the form of probability distributions until they interact with something (the object being blown up) and collapse into a single (randomly chosen) state derived from that probability distribution.

    How, in theory, could this be followed backwards to reconstruct the original object (deconstructed in the explosion)?
    Does not, going through the probability state collapse make exact predictions (of the results on the other side of the collapse) impossible?
    Would not causal actions proceeding through randomly chosen results of a probability function collapse not be predictable in theory?
    Would it not also be impossible to get all the needed information (position and movement) for each particle due to uncertainty issues?

    These seem to be theoretical blocks to recovering the initial states of the blown up object.
     
  16. Feb 8, 2017 #15
    When some thing gets into a black hole it gets destroyed,yeah.But due to that there is an increase in the energy and thus the temperature which accounts for the hawking radiation. Basically, we would get destroyed but that will not matter as the energy IS conserved.
     
  17. Feb 8, 2017 #16

    mfb

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    We don't know this. See post 2. Maybe, maybe not.
    No.
    There are interpretations without collapses. It is impossible to reconstruct the quantum-mechanical state exactly in every interpretation, that makes such a reconstruction impossible, yes. But if you would know the precise quantum state (in interpretations without collapses), you could do the reconstruction by simply letting time evolve backwards according to the laws of quantum mechanics.
    One more reason to avoid interpretations that introduce arbitrary, non-unitary, non-local, and generally weird collapses.

    If the black hole mass increases, the temperature decreases.
     
  18. Feb 8, 2017 #17

    anorlunda

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    It is very tricky discussing these things with natural language rather than mathematics, because of overloaded definitions of common words.

    For purposes of this post, let me define information as the number of possible states, and knowledge as knowing something about which of those states are most probable. An electron has two spin states; that's information. Observation may tell us which state it is in; that's knowledge.

    The conservation law discussed here is that the quantity of information is conserved (and look to Von Neumann entropy for a definition of that quantity). Your deconstruction example, shows that you are trying to interpret that as knowledge being conserved. They are not the same thing.

    Take an event, (a simple collision of two particles or a nuclear blast), it may destroy all knowledge of the pre-event statesk and chances for deconstruction, but the post-event quantity of information must match the pre-event quantity of information.

    Said another way, a system with N possible states can not have a time evolution into a future with other than exactly N possible states. That's called unitarity. That says nothing at all about knowledge of what the actual state is or was or will be.

    In everyday language, we often use the word information to be synonymous with knowledge. For example, what information do we have on that man? That is what makes these conservation laws so difficult to discuss. There is no natural language word that corresponds to Von Neumann entropy.
     
  19. Feb 8, 2017 #18

    BillTre

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    It sounds to me like you mean:
    The information is still there in the complexity of the states of resulting post-blast particles (or whatever), but the knowledge of their pre-blast arrangement will be (most likely) lost.

    So, when I am thinking of the information encoded as a written message on a piece of paper taped to an A-bomb:
    That information (in the diversity of post-blast states) is maintained numerically (due to unitarity), but the knowledge of the the message would rapidly become non-retrievable as the explosion progressed, due to the increasing number of state collapses over time.
    This seems to be than a theoretical limit to knowledge recovery then, if not information recovery. Yes? No?

    Does the knowledge of the original arrangement (the "information" in the message) then just become fuzzier as more time elapses (although the information (as counted by number of states) remains the unchanged)?

    That aside, if one requires complete knowledge of all the particles etc. coming out of the explosion in order to be able to back-calculate the initial state, does that require being able to get more information about the current states of things than uncertainty says is possible?
    This still seems like a theoretical limit to me, but maybe I'm not getting something.
     
  20. Feb 8, 2017 #19

    mfb

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    If the explosion happens in a perfect vacuum, and you build a gigantic quantum computer around the explosion to process the explosion products in a suitable way, you should find some operation that allows to retrieve the original letter. Purely theoretical of course, but within the laws of physics.

    You don't have to measure the precise state of everything. Just apply suitable operations to get as observable what you are interested in, e.g. the contents of the letter.
     
  21. Feb 8, 2017 #20

    anorlunda

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    I think the word that describes that is reversibility. Irreversible processes loose knowledge. Some processes are reversible, others irreversible.

    Simple mechanics of particles colliding is reversible. In theory, you can play time forwards and backwards all the way back to the pre-big-bang if you have perfect knowledge and huge computing capacity.

    If I take an electron with unknown spin and observe that it is up, then there is no chance of ever knowing what it's pre-observation state was. That is an irreversible process. I do not need to subscribe to wave function collapse interpretations of QM to make that irreversible.

    You should look up coarse grain entropy on Wikipedia. That gives you a classical picture of how knowledge can be systematically and irreversibly destroyed, while information is conserved. It is closely associated with entropy, and the second law of thermodynamics. As knowledge is destroyed, entropy increases.
     
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