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Delayed Choice Revisited

  1. Dec 2, 2008 #1
    Delayed Choice Revisited.

    Here is a very cut down summary of Wheeler's delayed choice experiment (hope I got it essentially correct):

    When a wave packet is half way between the screen and the double slits, a decision is made by the observer as to whether to look for a photon or a wave.

    If a wave is chosen to observe, then its intensity is due to the interference between the two paths from the slit - no problems.

    If the particle is chosen to observe, by essentially looking directly down both paths to the two slits, then a photon is indeed observed, which went down just one slit path as only a particle can do - no problems.

    The confusion, is caused, by the conflict between a particle going along a fixed single path, and a wave which 'must have been' in two paths at once. It appears as a contradiction.

    But using Copenhagen Interpretation, there is no contradiction because a wave packet is neither a wave or a particle, only a probability of observing one or the other. Only if the wave packet *interacts* with something on the way will decoherence take place. If it does not interact there is nothing to say what happened on the way, because on the way the position and momemtum remain unobserved - in superposition.

    It was a wave packet that made the journey, and that would have been in both paths at once!

    Then if a particle was observed that is the result of probability (wf collapse) at the receiving end.
    Likewise, the interference wave result is also the result of summation of wave amplitudes at the receiving end for waves in both paths.
    Last edited: Dec 2, 2008
  2. jcsd
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