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Macroscopic observation of interference?

  1. Jul 31, 2015 #1
    I suppose a related question is in regard to the fundamental nature of quantum superposition. Does any system in superposition "necessarily" demonstrate interference on a macroscopic scale?
     
    Last edited: Jul 31, 2015
  2. jcsd
  3. Aug 1, 2015 #2

    Nugatory

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    No. Consider that every particle in a macroscopic system is always in a superposition of something, yet demonstrations of macroscopic interference are extraordinarily difficult and rare. Decoherence provides a pretty good explanation for why this should be so; for a layman-friendly treatment I'd recommend "Where does the weirdness go?" by David Lindley.
     
  4. Aug 1, 2015 #3
    Thanks... I've got Lindley's book ordered. I'll give It a try.
     
    Last edited: Aug 1, 2015
  5. Aug 1, 2015 #4
    For whatever it's worth. Your answer is what I had previously understood. I just wanted to make certain I wasn't mistaken about that.

    The question seems to me to be fundamentally important with regard to the "pure" vs "mixed" status of a quantum state, which seems to be in dispute in a variety of on-going threads at present. The differentiation between the two seems to be frustratingly arbitrary, depending on how you look at it. Hopefully Lindley's book will provide some clarity on the subject.
     
  6. Aug 1, 2015 #5

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    Sadly, it won't. It's good, but it's not mathematical enough.
     
  7. Aug 1, 2015 #6
    Ugh. Let me ask you this then... Does this whole dispute ultimately come down to the ontological definition of the wave function?
     
  8. Aug 2, 2015 #7

    bhobba

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    Unfortunately no. The math is the only real explanation.

    Thanks
    Bill
     
  9. Aug 2, 2015 #8
    :) I don't want this to devolve into a philosophical discussion, but I think you know what I mean.

    I'm not debating the accuracy of the mathematical formulation. My question is in regard to the physical manifestation of WHAT the math refers to... assuming, of course, that there actually IS a physical manifestation.
     
  10. Aug 2, 2015 #9

    bhobba

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    The ontological status of the wavefunction is philosophy pure and simple. The math is silent on it - it can be just about anything depending on interpretation.

    Thanks
    Bill
     
  11. Aug 2, 2015 #10
    I guess that's my take away understanding from all this debate about the nature of pure and mixed (whether proper or improper) quantum states. The math is what it is. Discussion about what the math represents is frequently a semantic issue, and I don't see where it materially supports or refutes any of the typical QT interpretations.

    While the philosophical implications of these open questions obviously bother me more than they do you, I reluctantly accept that we simply don't know the answers yet... and maybe never will.
     
  12. Aug 2, 2015 #11

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    The math says that the off-diagonal terms in the density matrix, the ones that contribute to predicted interference effects when you do the calculations, will very rapidly decay to zero. The only thing that you could call a "physical manifestation" of this is that we don't observe the interference effects when the math predicts that we won't.

    That's about as far as you can go without getting lost in the swamp.
     
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