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I Some (unrelated) questions about the measurement problem

  1. Mar 20, 2018 #76

    haushofer

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    Yes, you're right, thanks.
     
  2. Mar 20, 2018 #77

    haushofer

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    I don't get this. I read the "cut" as the point where unitary evolution stops and collapse kicks in. Decoherence doesn't collapse anything, it merely makes the probability distribution classical.

    I have the feeling that you regard the "cut" as the border between classical physics (no interference, classical prob.distributions) and quantum physics. That's fine, but Von Neumann's chain is still problematic. You still need some sort of collapse or new principles to explain definit outcomes.
     
  3. Mar 20, 2018 #78

    haushofer

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    Well, Bhobba for instance :P I thought it was claimed also in papers, but to be honest I can't find them right now, so maybe I'm wrong.
     
  4. Mar 20, 2018 #79
    As Feynman said, it's always the whole Nature that is doing the job of incrementing her knowledge; so PhD, bacteria, cat etc. are mere various ways to participate in the game of Nature, like very different chess pieces (appearing as players).
     
    Last edited: Mar 20, 2018
  5. Mar 20, 2018 #80

    bhobba

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    It has a number of issues. There is an anesthesiologist that has some theory about it:
    https://en.wikipedia.org/wiki/Stuart_Hameroff

    For me it has far too many issues - but each to their own - it cant be disproved.

    Thanks
    Bill
     
  6. Mar 20, 2018 #81

    bhobba

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    Cut is where you can consider things classically from then on. If you put it after decoherence you are saying one of the possible outcomes is now objectively real ie it actually is in that state - but we don't know what state - such are by definition proper states. An improper state gives exactly the same probabilities of outcomes as proper ones - but is it in that state prior to observation? BM and MW would say yes - but others say no or who cares. There is no way to tell. But putting the cut right after decoherence is a simple way for things to be more understandable - for me and others anyway - of course each to their own who may think it total rubbish. For example the high priest of the Ensemble Interpretation Ballentine thinks its rubbish:
    https://marcofrasca.wordpress.com/2009/03/10/ballentine-and-the-decoherence-program/

    This is science - if it isn't what you like then you can view it anyway you want as long as its consistent with the formalism that everyone agrees on.

    Thanks
    Bill
     
    Last edited: Mar 20, 2018
  7. Mar 20, 2018 #82

    bhobba

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    I never claimed that. I claimed one can, if they wish, that an improper mixed state can be considered a proper one. This is the modern clear and unambiguous view of collapse - others for me don't make much sense - but each to their own. Its also a choice of where to place the Von-Neumann cut.

    Thanks
    Bill
     
    Last edited: Mar 20, 2018
  8. Mar 20, 2018 #83

    Lord Jestocost

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    It was "claimed" by some, but Stephen L. Adler, for example, cleared up the story:

    “Why decoherence has not solved the measurement problem: a response to P.W. Anderson” by Stephen L. Adler (Studies in History and Philosophy of Modern Physics 34 (2003) 135–142) https://arxiv.org/abs/quant-ph/0112095
     
  9. Mar 20, 2018 #84
    Isn't there, in accordance with the fundamental Schrodinger equation, that the system photon+detector+environment has an observable which could be used to find out if it is in a proper or improper mixture?
     
  10. Mar 20, 2018 #85

    bhobba

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    There is no way to tell the difference because they are exactly the same state.

    Thanks
    Bill
     
  11. Mar 21, 2018 #86
    All of this is evolution via the postulate of the continuous unitary process (Schrodinger), plus a tad of chaos. But there is also the postulate that measurements are random variables and the probabilities are not in principle derivable.
    How am I to reconcile the two postulates? I've received many conflicting answers and remain conflicted. Is this "the measurement problem"?
    You're my last hope, otherwise it's quantum suicide.
     
  12. Mar 21, 2018 #87
    #
    Under unitary evolution there is no selection of an eigenstate and no randomness.
    Histories are thus superposed.
    Probabilities emerge as frequencies in a history.
    The emergence of a preferred basis seems to be explained okay.
    All that's left of the measurement problem is dealing with the idea that there are actual probabilities as well. Seems simplest to say there aren't any but I'm told that that is philosophy and not part of science. :)
     
  13. Mar 21, 2018 #88
    Here is some information from a chapter written in the book referenced below, by Professor Jeffrey Barrett:
    upload_2018-3-22_7-30-29.png

    Corradini, A., & Meixner, U. (Eds.). (2014). Quantum Physics Meets the Philosophy of Mind: New Essays on the Mind-Body Relation in Quantum-Theoretical Perspective. Berlin/Boston: Walter de Gruyter GmbH.
     
  14. Mar 22, 2018 #89

    haushofer

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    Ok, I was quoting from e.g. this topic, https://www.physicsforums.com/threads/measurement-and-basics-of-qm.855073/page-3, which says

     
  15. Mar 22, 2018 #90

    haushofer

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    Ok, then I get your point. Thanks!
     
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