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Copenhagen Interpretation of Sleep / Unseen brain?

  1. Jul 6, 2015 #1
    What is the accepted interpretation of these two similar related issues:

    1) When I am sleeping do my brain and body revert to un-collapsed wave state until and unless seen by a different observer?

    2) I *never* have "seen" my brain - have the wave functions of the atoms and cells collapsed?
     
  2. jcsd
  3. Jul 6, 2015 #2

    Strilanc

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    Collapse is not caused by consciousness. All the experiments related to collapse have the same outcomes whether or not someone is in the room watching.

    You don't become any more superposed while sleeping than you do while awake, or while dead for that matter.
     
  4. Jul 6, 2015 #3
    Is this the Copenhagen approach? Is there no "measurement problem" ?

    Also: which interpretation of Wigner's friend is the most popular among experts?
    https://en.wikipedia.org/wiki/Wigner's_friend
     
    Last edited: Jul 6, 2015
  5. Jul 6, 2015 #4

    mfb

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    Yes.
    There is, but this has nothing to do with consciousness. Everything that causes decoherence counts as observation - which includes basically everything in our everyday world that is at least as large as a molecule, on timescales of at least picoseconds.

    Short naps seem to be a trend, but I did not see picosecond sleep discussed so far.
     
  6. Jul 6, 2015 #5
    So the standard Copenhagen is an "objective collapse theory" ?
     
  7. Jul 6, 2015 #6
    No. Decoherence causes apparent, subjective collapse. Decoherence occurs because of interactions of the object with an external environment and is not about the size or any property of the object itself per se.
     
  8. Jul 6, 2015 #7
    Every object is a wave, and when waves interact, they just make more waves. Where do the particles at particular positions come in? Is a direct "observation" required?

    If decoherence doesn't solve the measurement problem, then there isn't a tidy answer to my question, right?

    http://www.quora.com/Does-decoherence-solve-the-measurement-problem-in-quantum-theory [Broken]
     
    Last edited by a moderator: May 7, 2017
  9. Jul 6, 2015 #8
    Well, we don't know where collapse of the wave function occurs. It could be at the detector, or on the more extreme side it could be consciousness. Or we may find we need to modify standard QM to allow for collapse e.g. by gravity.

    By 'every object is a wave', I hope you don't mean wave in the classical sense.
     
    Last edited by a moderator: May 7, 2017
  10. Jul 6, 2015 #9

    mfb

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    It is not a lack of knowledge, it is a matter of taste - different choices lead to different interpretations.

    Neutrons bouncing above a surface follow QM with their states, I don't see much room for gravity having a special role.
     
  11. Jul 6, 2015 #10
    There is no correct answer as there are many interpretations, but there is an accepted interpretation of working physicists, which you asked for, that collapse is not caused by consciousness and apparent collapse is sufficient for all practical purposes.
     
  12. Jul 6, 2015 #11
    Yes - so can you flesh that out a bit. When is my sleeping brain just a probability wave and when are its atoms in particular positions, and what causes the change? Are "measurements" going on while I sleep? BTW what is the name for this "accepted interpretation of working physicists" ?
     
  13. Jul 6, 2015 #12
    I don't think there is any interpretation of QM which infers this.
     
  14. Jul 6, 2015 #13
    Your brain has activity going on when you are asleep, I would think.

    What superposition states do you think your brain will be in, while asleep?
     
  15. Jul 6, 2015 #14
    I am guessing decoherence, but I could be wrong.
     
  16. Jul 6, 2015 #15
    "Shut up and calculate" perhaps. :oldbiggrin: (Seriously! You can look it up.) Most physicists would just not care that the measurement problem is a problem. Maybe if you ask them why they will say something about decoherence, but that's about it.

    If you know (non-relativistic) quantum mechanics, the position is sort of already there as one basis that the quantum state can be represented in, along with other basis like momentum. What happens in decoherence is that the system is entangled with the environment through some interaction, and when you ignore the state of the environment, the density operator of the system appears diagonal in some basis. For some interaction, this is the position basis, and the "quantum probability" to be in different positions "loses its coherence" and become classical probability. That is, the system has some definite position, whether you see it or not.

    So the common answer is that there are so many interactions (with light, air etc.) going on with you body or your brain all the time that they are basically always classical i.e. decoherence has already occurred.
     
    Last edited: Jul 6, 2015
  17. Jul 6, 2015 #16
    That pretty much sums it up, but do remember the quantum system is not classical as only 'apparent collapse' has occurred. See pgs 208-210, 'Quantum Enigma' (2nd edition)
     
  18. Jul 6, 2015 #17
    A probability wave of one particle in my brain interacts with another probability wave in my brain and that is sufficient to cause decoherence? (doesn't solve the measurement problem.)
     
  19. Jul 6, 2015 #18
    Probability waves are not causally connected with the chemical state state of your brain. either awake or asleep.
     
  20. Jul 6, 2015 #19
    Something like that. Take a look at http://arxiv.org/abs/quant-ph/9907009, which probably became the standard view about decoherence in the brain. I don't know if there's a better estimate by now.
     
  21. Jul 6, 2015 #20

    bhobba

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    Yes there is - its just not unique. Decoherence however has morphed the issue to - why do we get any outcomes at all.

    The answer is called an interpretation of which there are a plethora.

    There is also the question of if its a problem to begin with - nature may simply be like that.

    Its called believing its not an issue to begin with. Mostly it worries philosophy types and those that work on the foundations of QM which is not what the vast majority of physicists do. Since deoherence has morphed the issue, they simply accept we get outcomes without requiring further explanation.

    Thanks
    Bill
     
    Last edited: Jul 7, 2015
  22. Jul 7, 2015 #21

    atyy

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    This is not universally agreed on. Whether Bohmian Mechanics can be extended to all relativistic quantum theories, and whether MWI makes sense are still generally considered open questions, eg. Wallace http://arxiv.org/abs/0712.0149.

    However, some of the very best have indicated they consider the measurement problem to be a problem including Landau & Lifshitz, Dirac, Weinberg, Tsirelson, Bell, Adler. Even von Neumann can be said to have worked on it, by trying to figure out whether hidden variables were possible.

    It's funny that I listed two of the co-discoverers of the chiral anomaly. Does Jackiw think the measurement problem is a problem? Jackiw's article with Shimony http://arxiv.org/abs/physics/0105046 describes the measurement problem (section 2.6), but mainly to report about Bell's views, so it seems unclear what Jackiw and Shimony's views are.
     
    Last edited: Jul 7, 2015
  23. Jul 7, 2015 #22

    bhobba

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    You know as well as I do we have many many different interpretations - not just BM or MW - and they each have a different take on the issue.

    And some of the very best like Gell-Mann, Ballentine and Bohr beg to differ. I am pretty sure Bohr believed it didn't have a measurement problem - at least that's what he argued with Einstein. Gell-Mann believes decoherent histories resolves it by removing observations from the theory. You cant just give those that agree with your position. Even Einstein believed QM was a perfectly valid theory of ensembles. Most physicists simply accept it at that level and don't get worried about deeper issues like Einstein did.

    Thanks
    Bill
     
    Last edited: Jul 7, 2015
  24. Jul 7, 2015 #23
    "Move on! Nothing to see here!"
     
  25. Jul 7, 2015 #24

    bhobba

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    No. It simply doesn't interest them. There is a difference.

    As I said, even Einstein believed it was a full and complete theory of ensembles. If you don't want to go deeper than that then you don't have to.

    Its like in EM there is runnaway acausal solutions to the Lorentz-Dirac equation:
    http://arxiv.org/abs/gr-qc/9912045

    You can view it as telling us something deep or simply reject them as unphysical. But most physicists, correctly, couldn't care less - it really makes no difference to what they do.

    To the OP there are some rather simple interpretations of QM that don't have any logical consistency problems at all - they give a full and complete account of all quantum phenomena. If you are not interested in what it means, like say Einstein was, then that's all you need.

    Thanks
    Bill
     
    Last edited: Jul 7, 2015
  26. Jul 7, 2015 #25

    atyy

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    No I am not aware of any which solves the measurement problem completely, with no technical issues. The major one I did not mention is Griffiths's decoherent histories, but that is certainly not widely agreed to be a solution of the measurement problem. Leifer https://mattleifer.wordpress.com/2007/03/26/teaching-quantum-theory/ and Laloe http://arxiv.org/abs/quant-ph/0209123 indicate problems with it.

    I am certainly not "giving only those that agree with my position". I was replying to your statement that most believe there is no problem, which stated without my balancing remark could give a misleading impression. Yes, as far as I can tell, Bohr and Heisenberg did not believe there was a measurement problem. If Gell-Mann believes decoherent histories resolves the measurement problem, then he does believe the problem exists (or existed) - otherwise what would there be no problem to "resolve". Also, Gell-Mann's version of decoherent histories is closer to the commonsense reality of MWI than Griffiths's version, eg. http://arxiv.org/abs/1106.0767.
     
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