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Measurement problem

  1. Jul 15, 2010 #1
    Is it correct to say that a measurement occurs whenever a wavefunction interacts with a macroscopic object? If this is the case why does the wavefunction make a distinction between a photon detector and say a half silvered mirror used in quantum experiments. Both are macroscopic objects but in one case the wavefunction collapses and in the other case it doesn't. I don't understand what is so different physically about a photon detector and a mirror. Both are fundamentally ensembles of particles. Why the difference in the way a wavefunction reacts to them?
  2. jcsd
  3. Jul 15, 2010 #2
    To me it would seem to be the manner of interaction. The detector is designed to detect and return a precise value for an observable. the half silvered mirror splits the beam and introduces less precision into the system. Such materials and shapses that make detectors are those that collapse wavefunctions. Such that expand them make mirrors. That's WHY the mirror is what it is, and the detector is what it is. You wouldn't make a detector out of a silver mirror. See what I mean?
  4. Jul 16, 2010 #3
    Is this process something that physicists understand or is it one of the still unsolved mysteries of QM? I'm assuming this is now understood in terms of decoherence but i'm trying to figure out exactly what decoherence explains. I understand that decoherence now provides a more illuminating explanation for what was previously thought of as wavefunction collapse but has it also demystified the fact that for apparatus set up to detect particles the wavefunction will collapse but apparatus such as mirrors will not cause wavefunction collapse. This is something i have never managed to get a clear explanation of.
  5. Jul 16, 2010 #4
    As far as I know, we haven't figured out exactly what it is about certain materials and configurations that cause them to interact differently, only that they do. We are just as mystified by the complex emergent properties of chemistry. The bottom line is that the N body problem just keeps rearing its ugly head wherever we look, Which essentially is an indication that our math is what isn't advanced enough to deal with these things. Just as calculus solved Zeno's paradox, I think there will be some new type of math that will solve the n body problem.

    Decoherence does not really explain why it is that certain types of matter absorb information like detectors do and other types do not. It would seem to me to require a better understanding of the quantum behavior of large atoms and molecules.
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