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Photons and Double Slit Experiment

  1. Mar 29, 2009 #1
    I read that quantum particles (like photons) travel as waves of probability, but when they encounter other quantum particles, the probability waves break down, and the photons assume properties of particles.

    An example given of this is: if you fire a single photon from point A, to a point B which is located on a solid surface, the photon will travel as a wave and in effect take all possible paths from A to B (loops, zig-zags, etc). And the photon will ultimately take the most probable path, and end up at point B on the solid surface.

    What I fail to understand is the double-slit experiment. Consider the example above. If you take that same solid surface, and cut two slits into it, and repeat the experiment, why would the wave of probability not disappear as soon as the photon hits the solid surface? Why does the wave continue to show interference on the other side of the surface just because there are two slits in the surface? If what I said above is correct (the emboldened part), the solid surface is made of particles, so the wave should break down on this side of the wall.
  2. jcsd
  3. Apr 2, 2009 #2
    Well, it appears that question was too much for everyone. But I believe I found the answer.

    In both examples above, the photon travels as a wave from where it was ejected to the wall, and in the second example the wave also continues through the two slits since these are possible paths. The probability waves I speak of apparently only exists for a very brief time until the detectors at the wall or behind the wall detect the actual path taken (once the photon hits either wall). Once the actual path is detected, the probability waves disappear.

    I failed to understand something that now seems obvious - the waves exist only while the photon is traveling from origin to destination, and since distances do not exist for particles traveling at light speed (as the photon does), the time for the photon to travel to the front wall takes just as long as the time it takes for the photon to travel past the front wall, squeeze through the slits, and hit the back wall. I was envisioning the photon wave traveling like a wave of water, which is apparently not exactly the case.