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Simultanous history

  1. Nov 21, 2004 #1
    As many people here will know, particles have wave-particle duality. A American scientist, Richard Feyman, suggested that when a particle move from a point to another, the particle can move through every possible route, not only one route (or history) as described in classical theory. The route we observed is the only possible route.
    The question is, if more than one route is possible will we observed more than one route?

    p/s: I am still learning quantum mechanic, please correct me if I am wrong.
  2. jcsd
  3. Nov 21, 2004 #2


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    No, we will not observe more than one route.

    The particle will follow every possible route - all states will be superposed - as long as it is not *observed*. When observed, the states all collapse to one, which we observe.

    This is what the two-slit experiment shows so clearly. If we do not observe which slit the photon passes through, then it passes through both, interferes with itself, and we see an interference pattern. If we put detectors at the slits, thus observing the photon, it is seen to pass through only one slit, and we get no interference pattern.

    Thus, when not observed, the photon has experienced multiple superposed histories. When observed, it has experienced only one history.
  4. Nov 22, 2004 #3
    Thanks, I think I know what you meant. But why must all states collapse to one when oberved? Is there a reason for this? Or this is just a fact without reason?
  5. Nov 22, 2004 #4
    The nature of measurment is that!!!
    When you say that the system is in one specified state , it means that if you make another measurment, you will find the system in that state again. If not, your measurment is not reasonable!!! and you can not trust on it. So every measurment put the system in the eigen state of the measured value
  6. Nov 22, 2004 #5


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    "But why must all states collapse to one when oberved? Is there a reason for this? Or this is just a fact without reason?"

    I believe 'fact without reason' is about right.

    I don't know if anyone knows the physics behind this yet - we undestand so little in this realm. It is only one interpretation of the observed data, afterall, and a hotly debated one at that. As we get farther and farther into QM, we find that the only meaningful answer is that there are no real-world explanations, and that it's all a matter of mathematical formulae.
  7. Nov 24, 2004 #6
    I think it is not just "a fact without reason"
    The argument behind it is about clear . Or maybe I think so!!!
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