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I What was Niels Bohr's rebuke to Schrödinger's Cat?

  1. Mar 3, 2016 #1
    Schrödinger came up with his famous cat experiment in order to attack the Copenhagen interpretation of QM.
    Since Bohr was the originator of the Copenhagen interpretation, what did he say about Schrödinger's cat?

    The way it is written in pop culture, many physicists believe that the entire macroscopic f***huge cat is in quantum superposition, and that the question is still unresolvable. This had led to many quantum mystics claiming all kinds of nonsense as a result, such as the belief that only a conscious observer can cause decoherence.

    I would like to know if Bohr came up with a reasonable explanation within the framework of the Copenhagen interpretation.
     
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  3. Mar 3, 2016 #2

    andrewkirk

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    Why is an explanation needed? There is nothing illogical or unexplained about Copenhagen. It's just that it conflicts with deeply held intuitions about ontology that many people seem to hold - specifically that every thing has a specific 'state' regardless of whether it is currently being observed.

    If we rejected ideas just because they conflicted with our intuitions, quantum mechanics would never have been accepted at all.

    I agree that Copenhagen specifically does seem to be latched onto by quantum mystics. But that's OK. It gives a boost to the publishing industry, which provides jobs and keeps people amused. It's irritating when quantum mystics ignore the distinction between the physics of QM and the metaphysics of QM interpretations, but compared with some other pieces of nonsense spoken about science (I'm thinking anti-vaxxers and climate change deniers) it's pretty minor.
     
  4. Mar 3, 2016 #3
    I'd say the opposite is true: there really isn't anything coherent about Copenhagen Interpretation. It's just some rules that work, but are completely at odds with the deterministic evolution of the Schrodinger equation. Though the Copenhagen Interpretation doesn't really have a set definition, so perhaps we should start with that before a conversation about it is possible.
     
  5. Mar 3, 2016 #4

    atyy

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    Decoherence does not require consciousness. It is measurement, and the retention of the measurement result that requires consciousness. It is not mystical, since we are conscious.
     
  6. Mar 3, 2016 #5

    bhobba

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    They may be how its written in pop culture - but its 100% for sure not true.

    Copenhagen's resolution is utterly trivial. The observation occurred at the particle detector. Everything is common-sense classical from that point on. The cat is never alive an dead - period.

    The purpose of Schroedinger's cat was to show, as Von Neumann also proved in his classical Mathematical Foundations of QM, where it is known as the Von Neumann Regress, is the quantum classical cut can be placed anywhere and that leads to problems. But nowadays decoherence is used to resolve it and you can find many threads here explaining that.

    Thanks
    Bill
     
  7. Mar 3, 2016 #6

    bhobba

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    It coherent all right. Its issue is in that interpretation QM is a theory about observations that occur in a common-sense classical world external to us. How does a theory that assumes such a world from the start explain it. A lot of progress has been made with that but some issues still remain.

    Thanks
    Bill
     
  8. Mar 4, 2016 #7
    It doesn't have immediate public safety concerns, but its still reflects on irrational ways of thinking. Still pretty bad I'd say.

    I believe that Schrödinger's catty objection must have been well-known back then, I just want to know what Bohr would have said to placate it.


    What is the definition of measurement/observation?
    Can we say that decoherence occurs the moment the radionuclide emits the particle?
     
  9. Mar 4, 2016 #8

    bhobba

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    The modern definition is when decoherence happens. But one can also take the view its a primitive of the theory like event in probability.

    Quantum theory predicts a probability a particle in a certain state will be emitted. The emitted particle will interact with the detector and is decohered.

    Thanks
    Bill
     
    Last edited: Mar 4, 2016
  10. Mar 4, 2016 #9

    bhobba

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    Its well known how Bohr resolved it - its exactly as I said:
    https://en.wikipedia.org/wiki/Schrödinger's_cat
    'However, one of the main scientists associated with the Copenhagen interpretation, Niels Bohr, never had in mind the observer-induced collapse of the wave function, so that Schrödinger's cat did not pose any riddle to him. The cat would be either dead or alive long before the box is opened by a conscious observer.[13] Analysis of an actual experiment found that measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement'

    Thanks
    Bill
     
  11. Mar 4, 2016 #10
    thanks bhobba. Can we say that Schrödinger misunderstood the Copenhagen interpretation?


    In this essay: http://plato.stanford.edu/entries/qm-copenhagen/
    von Neumann's view sounds like something those quantum mystics would love.
     
  12. Mar 4, 2016 #11

    bhobba

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    No. He, as I said, was alluding to a genuine issue - the Von Neumann regress.

    He started this conciousness causes collapse thing to break the regress. Since any place to put the quantum classical cut is as good as anywhere else he placed it at the concious observer. Its now outmoded because we know a place that's different - just after decoherence.

    Von Neumann died young but Wigner was also an advocate. He saw some of the early work on decoherence by Zureck and did a 180% about face realizing it was no longer required.

    Thanks
    Bill
     
    Last edited: Mar 4, 2016
  13. Mar 4, 2016 #12
    180%? or degrees? I would like some documentation of this to shut down the quantum mystics who keep quoting Wigner.
     
  14. Mar 4, 2016 #13

    bhobba

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  15. Apr 29, 2016 #14
  16. Apr 29, 2016 #15

    bhobba

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    There was a reason for it. Read Von Neumann's Mathematical Foundations of QM.

    Von Neumann was one of the smartest guys that ever lived, quite possibly in the top 10 mathematicians of all time, but he was much much more than a mathematician - he was a polymath. He could penetrate so quickly and easily many thought he was the only person fully awake. He did not do it lightly. The reason he did it no longer applies but at the time it seemed a good idea with good reason.

    Thanks
    Bill
     
  17. Apr 29, 2016 #16

    phinds

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    I'm reminded of a quote which I've heard attributed to a couple of different people: "There are two kinds of people in the world: Von Neumann and the rest of us."
     
  18. Apr 29, 2016 #17

    berkeman

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    Thread closed for Moderation...
     
  19. Apr 29, 2016 #18

    PeterDonis

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    The OP's question has been addressed. This thread will remain closed.
     
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