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B Information paradox in black holes

  1. Mar 21, 2017 #1
  2. jcsd
  3. Mar 21, 2017 #2
    If you accept the theories, then everything is encoded on the quantum bits, including black holes. The article also mentions holographic theory. In holographic theory, it might not be meaningful to talk about the inside of a black hole. All the information of a black hole is encoded on a surface. I don't know rigorous these theories are at the moment, so it's hard to say if any of it is true.

    The idea that a black hole can be described by just the mass, charge, and angular momentum is not consistent with black holes having a temperature, and is probably just incorrect. Some scientists are seeing evidence for echos in the gravitational wave emission from black holes which flat out contradicts the mass/charge/angular momentum idea. http://www.sciencealert.com/echoes-...-a-breakdown-of-einstein-s-general-relativity
     
  4. Mar 21, 2017 #3

    Chalnoth

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    How is it not consistent with black holes having a temperature? The temperature is not an independent variable, but is a function of its mass.

    Usually these sorts of things don't pan out. We'll need a lot more data to be sure that something is actually going on here.

    It would honestly be wonderful if General Relativity broke down outside the event horizon, so that we could actually measure the deviations. But I'm not sure that we'll get that lucky. As long as General Relativity is valid, however, the no hair theorems prove that a black hole only has those as independent variables.
     
  5. Mar 21, 2017 #4
    You can't have temperature without entropy. Entropy means there are internal degrees of freedom that we are not keeping track of.
     
  6. Mar 21, 2017 #5
    The article mentions quantum bits made up spacetime. Do you mean the information is encoded in spacetime itself? But when the black holes evaporate and spacetime dissolves.. where did the quantum bits of spacetime go?

     
  7. Mar 21, 2017 #6
    When a black hole evaporates, the information of the black holes is contained in the Hawking radiation.
     
  8. Mar 21, 2017 #7

    Chronos

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    It was already apparent black holes have an enormous amount of entropy, Hawking basically just connected the dots from there by logically deducing the laws of thermodynamics demanded a BH to have a effective temperature to remain consistent with what we already knew of physics. It's 'temperature' just reflects this reality. Naturally, a body with a boat load of entropy should have a very low temperature, which is absolutely the case. A stellar mass black hole is scarcely any warmer than a patch of empty space far from the nearest star. It has no basic processes going on, like nuclear or chemical, capable of radiating energy, so a black hole's temperature is unlike a temperature emission in any classical sense. It is more like the waste heat from an astoundingly efficient refrigerator. You just can't suck those last few nano kelvins out of any space without running afoul of quantum mechanics. Only a tiny [low mass] BH can even emit enough energy via Hawking radiation to be detectable against the backdrop of empty space and that is still just a conjecture. We've never actually seen a BH small enough to have a measurable temperature. Such a BH could very well be a veritable Boltzmann's unicorn, given the universe is far too youthful to have permitted any naturally ocurring [i.e., via gravitational collapse] BH to have radiated away enough mass to qualify as 'tiny'. Nothing is forever, but, a BH is about as close as you can get.
     
  9. Mar 21, 2017 #8
    Were you describing the Firewall thing? Because without the Firewall, the information can't be contained in random quantum pairs radiating as Hawking radiation.
     
  10. Mar 22, 2017 #9

    Chalnoth

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    In a sense, but it also means that no useful information can ever be extracted from those degrees of freedom. So in the end it amounts to the same thing, unless general relativity breaks down outside the horizon and the no hair theorems fail.
     
  11. Mar 22, 2017 #10
    I think that in the next few years we will discover that the no hair theorem is false. We will have more gravitational wave measurements by then.
     
  12. Mar 22, 2017 #11

    PeterDonis

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    This is a current hypothesis, but we don't know for sure that it's correct. One obvious issue is how the information gets transferred to the Hawking radiation.

    How will gravitational wave measurements affect the no hair theorem? Gravitational waves are not emitted by stationary black holes, which are the ones that the theorem applies to.
     
  13. Mar 22, 2017 #12
    Gravitational wave echoes. https://arxiv.org/abs/1612.00266
    Seen at 2.9 sigma significance. Not enough to be called a discovery, but in a few years, we might see something more significant.
     
  14. Mar 22, 2017 #13

    anorlunda

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    If the Hawking radiation has states and carries information, where else could the information come from?
     
  15. Mar 22, 2017 #14
    To rephrase my original question in thread #1 which was unanswered. If spacetime was really built from quantum bits. Does the concept mean the quantum bits (tensor networks, etc.) just built up spacetime or does it mean information outside can be encoded in the quantum bits of spacetime? Are the two separate concepts or related? Reference:

    https://www.quantamagazine.org/20150428-how-quantum-pairs-stitch-space-time/

    "Tensor networks provide a mathematical tool capable of doing just that. In this view, space-time arises out of a series of interlinked nodes in a complex network, with individual morsels of quantum information fitted together like Legos. Entanglement is the glue that holds the network together. If we want to understand space-time, we must first think geometrically about entanglement, since that is how information is encoded between the immense number of interacting nodes in the system."
     
  16. Mar 22, 2017 #15

    Haelfix

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    Where indeed, that's what the big fuss is about! You can actually formulate a theorem that Hawking radiation CANT be what carries the information out, unless you accept that this constitutes O(1) departures from classical relativity and in particular the no hair theorem is violated by very large macroscopic effects. If you don't like that conclusion, questioning the assumptions of this theorem directly leads to the firewall argument.
     
  17. Mar 22, 2017 #16
    Is it sure that information cannot be destroyed?
    I thought that information is encoded in some way that could be called meaningful.
    What is meaningful about Hawking radiation, a mashup (if it exists), of random photons.
     
  18. Mar 23, 2017 #17

    PeterDonis

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    It is if quantum unitarity is correct. One of the proposed ways of getting around the black hole information paradox is the hypothesis that unitarity is violated in processes involving black holes. It's not a very popular proposal AFAIK.

    No, there isn't. "Information" is really just another way of referring to the microstate of the system.
     
  19. Mar 23, 2017 #18

    Chalnoth

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    Yup. One way of thinking about entropy is with regard to information: the difference between the entropy of a system and its maximum entropy can be related to the amount of "useful information" in the system. We generally expect that the microstate of the system will follow deterministic, reversible laws (which is related to unitarity). In that sense, the total amount of information in the system is conserved. But as the entropy increases, that microstate becomes highly randomized, so that you can't use it to make a car move or store the contents of a book. In that sense, it's no longer useful.

    The Hawking radiation that comes from a black hole is near-equilibrium in the sense that its emissions rate and pattern have no measurable connection to the matter that fell into the black hole: it's purely thermal radiation. So, sure, it is perfectly plausible that the microstate of the system follows unitary laws of physics, but the black hole does such a good job of randomizing that information that it can no longer be interpreted in any realistic sense.
     
  20. Mar 23, 2017 #19
    my questions go like this...

    1. Let's say spacetime has discrete quantum bits (like those Tensor Network things or even the spinfoams in LQG)
    2. information falls into black hole
    3. information gets encoded into those fundamental spacetime bits
    4. When black hole evaporates.. does the information encoded in the spacetime quantum bits need to come out as Hawking radiation or it is simply converted into pure bits that stays there in space even after the black hole evaporates (so imagine spacetime shredding into into pure bits).. this means the information doesn't come out as Hawking radiation but in other forms.. why is this not possible? what laws of physics forbid this process?
     
  21. Mar 23, 2017 #20

    PeterDonis

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    The answers go like this: we don't know. We don't have a theory of quantum gravity. All we have are various hypotheses and no way to run experiments to tell which ones are right. The "quantum bits" thing is just one such hypothesis.
     
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