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Thread: OT: Double slit experiment

  1. #11
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    The real beauty of that experiment is if you reduce the intensity of the light to the point where only a single photon passes through the slits at a time, the interference pattern is still built up over time. You need to use film to record the strikes of the individual photons and you have to run it for many hours or even days before developing the film.

    But a single photon can only pass through one of the slits. Yet due to it's dual particle/wave nature, it "knows" about the other slit and it behaves as if it interfered with another photon that passed through that other one. You don't get what you would expect as the superimposition of the pattern for two individual slits, which would not be an interference pattern. You get the actual interference pattern, just as happens with more intense levels of light so the light from the two slits can interfere with each other. In effect, a single photon can pass through both slits and interfere with itself.

    As one physicist said, probably paraphrased a bit, the world in not just stranger than we think it is, it is stranger than we CAN think it is.
    Paul A.

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  2. #12
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    We never had lasers back in high school. But we still did the experiment.

    I may also have mixed up diffraction with interference. The deal we did with the slit was a single slit so that's diffraction. We did a different experiment for interference but it wasn't the slide with black paint and razor cuts.

  3. #13
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    Quote Originally Posted by Paul Alciatore View Post
    The real beauty of that experiment is if you reduce the intensity of the light to the point where only a single photon passes through the slits at a time, .
    we've all read of the experiment before (or assume so) and had our brains hurt as a result, where I get confused is how does one emit a single photon
    .

  4. #14
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    Quote Originally Posted by Mcgyver View Post
    we've all read of the experiment before (or assume so) and had our brains hurt as a result, where I get confused is how does one emit a single photon
    With some difficulty. The first single-photon source was made in 1974. Some of the laser guys at work with built a single photon source for an experiment. As far as I know, it's still in the basement.

    I did the dual slit experiment with electrons and a Mollenstedt interferometer instead of light and slits when I was in undergrad. Macona here on the forum actually sent me some vacuum parts to accomplish it. The idea was to eventually de-focus my electron source to a point where I could be reasonably certain of single electrons propagating through the interferometer. The electrons were incident on an extremely sensitive phosphor coating; the coating and electron energy were chosen such that a single electron would yield enough light to be visible. I never made it that far, though. I was able to get the expected results with large numbers of electrons but wasn't able to attenuate my electron source down to single electron level.

  5. #15
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    I wonder if photons can pass through a graphene lattice. If not, one could search through sheets of graphene until they find one with a single broken lattice and use that as a pin-hole for single photons to pass through -- or however many neighboring broken lattices are needed until a single photon can pass though at a time.
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