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Proof that black holes do not destroy information

  1. Oct 12, 2014 #1
    I have for you a simple proof that black holes do not destroy information, since wikipedia seems to be stating that it's an unsolved problem. http://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics

    1. The second law of thermodynamics states that entropy must always increase.
    2. If black holes destroyed information, that would lower the overall entropy of the universe.
    Therefore, black holes cannot destroy information.

    However I'm near certain it isn't that simple. What's wrong with this proof?
  2. jcsd
  3. Oct 12, 2014 #2


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    Well, for a start, we say that black holes have entropy - see articles on Black Hole Thermodynamics.

    But otherwise, what you've said isn't actually a proof, it's a restatement of the problem: Our understanding is that black holes destroy information, but that violates unitarity, and energy conservation, and all that fun stuff that we think has to be true in the universe. So something has to give. This is why it is an unsolved problem.
  4. Oct 13, 2014 #3

    Simon Bridge

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    Welcome to PF;
    You statement requires that (1) is true everywhere - even in black holes, and it equates "loss of information" with lower entropy.
    So if both those things are true, the (2) must also be true.

    But here's the thing - no information can travel faster than light.
    Therefore, information cannot escape a black hole.
    See the problem?

    So your starting points are
    (1) entropy must always increase
    (2) information cannot escape a black hole
    (3) information is entropy

    For more um information...

    Black holes, entropy and information (lecture)

    information is not uncertainty

    information cannot get out of a black hole

    ... but it is a popular topic so there's lots and lots about it.
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