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B Big Crunch, Big Bang and information loss

  1. Jul 20, 2017 #51

    kimbyd

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    Depends a bit upon what you mean by information.

    If by information you mean the full configuration of the wavefunction of the universe, then as long as the laws of physics are unitary the two points in time necessarily contain the exact same amount of information. This means that if you had the full state at the early time, you could calculate the late time knowing the laws of physics. If you had the full state at the late time, you could calculate the early time.

    It comes down to whether or not the laws of physics are unitary.
     
  2. Jul 20, 2017 #52
    By information, I mean all the relevant data and conditions regarding a particle that would provide me a clear enough picture that I could solve that particles prior or subsequent motion, action, interaction, and nature with certainty.

    I'm guessing that proving if the laws of physics are unitary, or not, is probably not going to be able to be determined in this thread, nor by anyone in the near future, right?
     
  3. Jul 20, 2017 #53

    kimbyd

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    Yes, that's more or less the definition I assumed.

    Correct. Unitarity is currently unknown, though many physicists suggest the fundamental laws must be unitary to have a sensible notion of causality. I gave an overview of what current physical laws are/aren't unitary in post #13 of this thread.
     
  4. Jul 20, 2017 #54
    I'd say way back when all the forces were unified would be the most likely bet at having a coherent picture of things, after gravity separated you get into what we have now, spin foams and such to deal with...
     
  5. Jul 20, 2017 #55
    I think I have the answer I asked for, thank you everyone.
     
  6. Aug 1, 2017 #56
    "What I am trying to get at is if there really is any new information being generated in the universe, or if the entire cycle of the universe, including a potential future big crunch or big whimper wasn't already predetermined at the moment the big bang came into existence or 'occured.'"

    So were the works of Shakespeare predetermined at the "big bang"?

    The notion that information simply "crystallizes out" as the universe evolves is seductive but our observation that much of the machinery of nature is essentially probabilistic really rules it out.

    Furthermore we can safely assert that information is not conserved since simply burning a CD destroys the all extrinsic information impressed upon in as well as most of the intrinsic information inherent in its molecular structure.


    Reference https://www.physicsforums.com/threads/big-crunch-big-bang-and-information-loss.919985/
     
  7. Aug 1, 2017 #57

    PeterDonis

    Staff: Mentor

    No, it doesn't. It just transfers the information to a different physical form. In principle, if quantum unitarity is correct, you could take the combustion products, analyze them, and compute all of the bits of information in the CD.
     
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