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How is information conserved in a black hole?

  1. Jul 14, 2010 #1
    I was curious, please explain to me in an easy way of understanding because I am not the best at picking things up. Thank you.
  2. jcsd
  3. Jul 15, 2010 #2
    The answer is simple, but not very satisfying... No one knows. There's lots of equally 'good' ideas which, as yet, don't have any means of distinguishing between them via observation or experiment. Thus there's no consensus on the issue.
  4. Jul 15, 2010 #3
    Did Stephen Hawking say that information was destroyed by a black hole?
  5. Jul 15, 2010 #4
    Yes, but then he was refuted sometime in the early decade of 2000. I want to know how he was refuted.
  6. Jul 15, 2010 #5
    Also wasn't Linard Susken involved?
  7. Jul 15, 2010 #6
    Leonard Susskind. Yes, he was. He has a book about the whole debate which you might do well to read to get the full story, "The Black Hole War".
    Last edited: Jul 15, 2010
  8. Jul 15, 2010 #7
    He (Stephen Hawking) refuted himself apparently, but there's no easy explanation for what his work implies, nor is it widely accepted. It involves a quantum cosmology approach called "Many Histories", but it's hard to explain - I don't understand all its subtleties myself.
  9. Jul 16, 2010 #8
    Thank you for recommending the book. I will get it and learn more.
  10. Jul 24, 2010 #9
    Recently I watched a show on the Science channel called "Through the Wormhole with Morgan Freeman". I think the topic is discussed in http://www.youtube.com/watch?v=BjJ4A9GP0As". The rest of the segments are available on youtube as well. It might be worth checking out.
    Last edited by a moderator: Apr 25, 2017
  11. Jul 26, 2010 #10
    I do not think information is conserved in a black hole. They do radiate, but this radiation is random.
  12. Jul 26, 2010 #11
    what if we are taking the black hole wrong way?
  13. Jul 26, 2010 #12


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    What information is lost? Do stars 'absorb' information? Black holes emit hawking radiation, that satisfies the issue.
  14. Jul 26, 2010 #13
    Chronos, do you understand the difference between information and random radiation?

    For instance assume an astronaut falls into a fully formed black hole. All the information about him, his length, the color of his eyes, the number of atoms in his body etc will be destroyed in finite time after he passes the event horizon. All that will ever be returned about him is random radiation.
    Last edited: Jul 26, 2010
  15. Jul 26, 2010 #14
    We are discussing Hawking radiation at this point right?

    The way I understand this is that Hawking radiation isn't from things that fall into a black hole. One of the quantum theories postulates that at every point in space, little pairs of matter and anti-matter form, separate, and annihilate each other in a fraction of a second. If a pair forms just outside the event horizon, one of the pair can get sucked into the black hole and the other can travel into space thus producing radiation around a black hole. Note that this radiation does not actually come out of the black hole (nothing can ever come out of a black hole). Hence, we still have an issue with conservation of information. Even if our astronaut were returned in random radiation, we could still, in theory, follow every piece of radiation back to his original body. But with a black hole, you literally can not retrieve any information about him, it is gone from space-time. Check out the youtube link I posted before for more information on conservation of information. I don't understand the solution well enough to comment on it.

    Once again, that's just the way that understand the situation and I'm no cosmologist. Please correct me if my information wrong
  16. Jul 27, 2010 #15


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    Hopefully I do, passionflower. Black holes eventually [very eventually] evaporate via Hawking radiation. Hence, any 'missing' information is ultimately returned to the universe [albeit mangled] via the combination of Hawking radiation and the final 'poof' when the black hole finally evaporates. It all hinges on how you define 'information'. Many scientists would characterize information loss as a form of entropy. I'm ok with that.
    Last edited: Jul 27, 2010
  17. Jul 27, 2010 #16
    I disagree. It is true, we currently understand Hawking radiation by way of a semiclassical approximation, in which classical information entering the black hole is completely destroyed (no hair), and on the other hand, thermal radiation from the black hole is truly random (no correlation with whatever went in).

    But I think that's an artifact inherent to the approximation. Most would expect that a true quantum gravity theory will still be unitary (or that in principle the wave function of the universe would be deterministic and reversible regardless of black holes having evaporated), thus information is no more lost in black holes than it is in other quantum processes. In other words, if you could isolate the black hole (from decohering with the environment) then in principle there would be some way you could ultimately recover your astronaut (perfectly, but surely not with less difficulty than recovering information fallen into a burning star).
    Last edited: Jul 27, 2010
  18. Jul 30, 2010 #17
    Hawking Radiation as it is currently formulated doesn't return information; the production of the radiation in no way reflects what fell into the BH. This is a central issue of the IP, which may be solved by others, or Hawking himself. One of the more popular notions remains that the information is 'encoded' in minute fluctuations of the event horizon, but HR is still random.

    If HR is it, and there is no remnant (generally ruled out for many good reasons) or other means of preserving the information then BHs do destroy information. We await what Cesiumfrog has posted about, or something like the Holographic Principle to resolve the paradox, otherwise black holes break Unitarity.
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