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What is information in a black hole

  1. Sep 18, 2011 #1
    May be am taking you a way too back, but I really don't understand what this Information in a black hole is !! Ive bin reading about it for the past 2 days but could understand it in no way....Is it anyway physical?? and this sentence is almost killing me : Information gradually leaks out during the black-hole evaporation ... Whats this information about and how can some abstract thing leak?? Could anyone kindly explain it for me ? Thank yo :)
  2. jcsd
  3. Sep 18, 2011 #2
    I have wondered about this as well. The only time I heard of how things actually get out of a black hole is when I read The universe in a nutshell. It said that there are things called zero-point fluctuations in a vacuum in which a particle and antiparticle are created then annihilate each other almost instantly. When this happens at just the right distance from a black hole the particle escapes and the antiparticle is pulled into the black hole slightly decreasing the mass and releasing the particle as radiation. I don't think this could carry information so I think there must be something else I'm missing.
  4. Sep 22, 2011 #3
    Exactly...this is how matter/energy leaks out of a black hole. and it's a realllly slow process...taking more than the total age of universe for a black hole to evaporate
    And by matter, we can mean information.
    ( Somewhere I read that even emission of heat from digital circuits can be associated with loss of information...like when you 00101101|00000111, we get 00101111 and the 2 bytes lost, 1 byte gained->1 byte lost. maybe in the same way, loss/gain of matter can mean loss/gain of information. )
  5. Sep 22, 2011 #4
    :cry: What does the Information exactly mean?? Does it mean details about that particular black hole or anything else?? Please try to think it keeping the dictionary meaning of Information in your mind. because I really want to know if it means the same as that we use in our daily usage or any other Astrophysics meaning is underlying in it . Thank yo :)
  6. Sep 23, 2011 #5


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    From this wikipedia article: http://en.wikipedia.org/wiki/Schwarzchild_singularity


    See this article for more on the effect: http://en.wikipedia.org/wiki/Black_hole_information_loss_paradox

    P.S. Wikipedia is your friend!! :biggrin:
  7. Sep 26, 2011 #6
    Think computer memory. I have a flash drive that has 8GB. Which means that it can store 8 billion bits of data. I take that flash drive and burn it. I've just destroyed information, which means that the entropy of the universe has increased.

    I take my flash drive put it into my computer and then upload it to facebook. I've just moved bits of information from the flash drive to the facebook servers.
  8. Oct 4, 2011 #7
    Thanks for the explanation :approve:
  9. Oct 5, 2011 #8
    I think I can elaborate on what twofish said, the content of this information is the questions we can ask particles. What is the position of the particle? Momentum? Does it have spin? Electric charge? It is the answers to similar types of questions that people worry about when black holes evaporate.

    A particle can go into a black hole, but it cannot get back out. So the information about its spin and other properties become part of the black hole. The black hole will eventually evaporate. People are worried that the radiation coming out of the black hole simply does not care about how the black hole grew. The particles that went in seem to have no effect on the radiation coming out. Therefore, once the black hole disappears, the information about the particles once carried will disappear along with the black hole.

    A black hole can be described by its mass, electric charge, and angular momentum. The radiation coming out will be affected by these properties only. But correct me if I am wrong.
  10. Oct 6, 2011 #9
    Yup. Here is the problem.

    Suppose I have a flash drive with youtube pictures and then I smash it with a hammer and then burn the pieces. As a practical matter I can't reverse the process and figure out what was on the flash drive. However, the rules of physics are time invariant, which means that even if I can't *practically* recover the pictures, the exact configuration of the final product corresponds with original pictures. So I could in principle take a super-duper computer, and work backwards and compute what was on the flash drive.

    Now if I take some of the ashes and toss them into a black hole, then that information is *gone forever*. I can't see inside the black hole, and I can't reverse calculate what was in the flash drive. Something weird is going on since this seems to violate the rule that the laws of physics don't destroy information.
  11. Oct 6, 2011 #10


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    The problem centers around determinism - a logic based essentially on the classical concept of 'what goes up must come down' - which is refuted by quantum mechanics. Information is like currency - neither created or destroyed, merely exchanged. Assuming black holes 'leak' [hawking radiation], I see no paradox.
  12. Oct 6, 2011 #11
    If it were that easy to fix the problem I doubt that Stephen Hawking, Leonard Susskind, and Gerard 't Hooft would be arguing over this.

    The problem is that the equations of quantum mechanics are deterministic. Given a wave function, the time evolution of that wave function is fixed, and you can define information in quantum terms such that the total amount of information is conserved.

    Also, be careful about analogies. The example I'm using of crushing a flash drive is the best thing I can think of to illustrate the problem to someone without writing integral signs. As with all physics analogies, they simplify a lot of stuff.

    The statement about currency is false (and dangerously false), but that's another thread.

    That's the problem. If information were not destroyed, then what goes into the black hole should affect the Hawking radiation that comes out, but that idea contradicts the idea that black holes have no hair. The other problem is the singularity. If I toss a flash drive into a black hole, and it somehow floats in the black hole, you can imagine that it will somehow affect the radiation coming out, but that's not what happens (or is it?).

    What happens if you use GR is that the flash drive gets crushed to a singularity long before there is any Hawking radiation. Now maybe somehow the singularity influences the Hawking radiation, but if that happens we are outside of standard GR and QM (not to say that that's a bad thing.)

    The point of this paradox is that something is broken in theory. Now the way you figure out what happens is to take a black hole, toss something in, and see what happens, and oddly enough, we should very soon be able to do that....

    Last edited: Oct 6, 2011
  13. Oct 7, 2011 #12
    I don't believe this can be said of the Born rule.
  14. Oct 27, 2011 #13
    It's even trickier than that. I take a ice bit. I write some information of incalculable interest on it. Like my girlfriends home number. I forget to put it back into the refrigerator. It melts. I haven't done a thing to the molecules atoms etc, I just rearranged them slightly for this 'information'.

    How do I get the information back?

    If I don't she will think I lost interest :)

    There's a lot of 'information' that is not deciphered by spins, like thoughts.
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