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The black Hole Wars - Losing Information in the Hawking Radiation

  1. Jun 23, 2014 #1


    So as I understand it, Hawking theorized that due to the behaviour of virtual particles on the event horizon of a black hole, eventually the black hole would "evaporate" through what was coined the Hawking Radiation. But what I'm curious about is Hawking's interpretation of the event in that information would eventually be lost. Is this truly the case? How is information actually lost inside a black hole? Why is it that a positive particle can escape the velocity of a black hole yet a negative particle can't? Are positive particles for a lack of better words "magnetically repelled" by the black hole? I just don't understand how this concludes that information has been lost, and why it requires Susskind's solution of the Holographic Principle to resolve this issue. Any input is appreciated!
     
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Jun 23, 2014 #2
  4. Jun 23, 2014 #3

    Bill_K

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    First thing to realize is that despite all the public attention, Hawking Radiation is very much an "in principle" thing. It's incredibly weak, plays no part in the astrophysical processes that go on around black holes, never been observed and probably never will be!

    It's a global phenomenon, meaning that it takes place in the region surrounding a hole, not on the horizon.

    This video carelessly refers to "positive/negative particles", or "positive/negative mass particles". No such thing. They mean to say, virtual particles with positive/negative energy.

    The point is, the same radiation comes out (namely a mixture of everything!) regardless of what went in to make the hole in the first place. If the hole evaporates completely, there's no way to tell any more if the infalling stuff had been protons, electrons or whatever.

    Hawking has NOT changed his mind about the information loss. And the "apparent horizon" stuff is not due to him, it's due to Polchinski and he disagrees with it. Quoting from Hawking's talk,

     
  5. Jun 23, 2014 #4
    Thanks. The thing is, is information really lost? Or are we just lost? Couldn't one argue that classical and quantum information is just made out of the same building blocks of matter regardless of what the radiation turns into? It seems more a conceptual idea that information is lost rather than an actual problem in physics that needs solving with ideas such as the Holographic Principle. Surely if you understood enough about the system then the information could be regained? This where I don't understand how the information was lost and why it was considered an issue that needs resolving.
     
  6. Jun 23, 2014 #5

    Bill_K

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    It's only an issue in the most abstract sense. But to people who think about abstract things, it's an issue!

    Suppose I write my telephone number on a piece of paper. Now I light a match and burn the paper, leaving nothing but ashes. In principle, if I watch the burning process, I can rearrange the atoms in the ashes back exactly the way they were and recover the phone number! No information has been lost, it's just been made a lot more difficult to access.

    But now suppose instead I dropped the paper into a black hole. Conventional wisdom tells us that in this case the number is absolutely irretrievable - the information has been lost. In fact, all you can ever know about a black hole is its total mass, total angular momentum and total charge. This is referred to in the Hawking quote as the "no hair theorems". Information loss is a violation of an important principle in quantum mechanics called unitarity.

    Well as long as you have the hole sitting there, people hoped against hope there might be a way to retrieve such lost information. But if Hawking Radiation evaporates it completely, it's obviously gone. The radiation doesn't cause the information loss, but it drives the last nail in the coffin.
     
  7. Jun 23, 2014 #6

    marcus

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    Currently the most cogent model (incidentally also observationally testable) of BH I know of is the Planck star model.
    In that model all the info comes back out in a final gamma ray burst (GRB) explosion which completely destroys the BH.
    This was proposed in early 2014. It will be discussed at the September 2014 conference on "Experimental Search for Quantum Gravity". We'll see how that goes. You can google the conference name to get the website.

    You can google "planck stars" to get the original January 2014 paper for pdf download on arxiv.org.
    You can google "planck star phenomenology" to get a followup paper on observational predictions (what to look for in the sky if the model is right) also on arxiv.org.

    The earlier model of BH and BH evaporation was fraught with contradictions and paradox. that is what Hawking, Susskind, Polchinski etc etc. are talking about. Several exotic resolutions of apparent contradictions have been proposed. Most recently Susskind and others been playing with a couple of escape-hatch ideas---firewall (2013) and computational complexity (2014). Essentially ways Nature might prevent an observer from getting the same information twice or from decoding info which was somehow there but not accessible. I don't know that it is worth discussing.

    Planck star model resolves the apparent paradoxes in a simple straightforward way. The info only comes out once, at the end. It is delivered up when the BH explodes and spills its guts at about 60% of the way thru its Hawking estimated lifetime.

    We have a Planck star thread in the BtSM forum. Also there has been some popular media coverage that you can probably find by googling, if you want.
     
  8. Jun 23, 2014 #7
    This makes sense to me, thank you!

    Lots of information to look in to, thanks! I might have to watch that conference in September!
     
  9. Jun 23, 2014 #8


    This seems like a nice video!
     
    Last edited by a moderator: Sep 25, 2014
  10. Jun 24, 2014 #9
    Could an analogy for lost information in the Hawking Radiation be like an ice sculpture melting? For an ice sculpture might take the image of a beautiful swan, but once the ice sculpture melts all you have is a pool of water. Would it be impossible to tell what the ice sculpture was simply by studying the pool of water on the floor?
     
  11. Jun 24, 2014 #10

    Bill_K

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    This is similar to the example of burning paper that I gave in #5 above. (And it's not my example, it's due to Hawking.) The apparent information loss (increase of entropy) happens because we fail to keep track of exactly what happens to each atom. If we do keep such a detailed account, then in principle there is no information lost, in either example.

    The point of the example was that using a black hole as a garbage disposal is qualitatively different, and really does lose information.
     
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