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Questions about variations on Double Slit experiment

  1. Aug 3, 2009 #1
    I've been wondering about the implications of this experiment and have a couple of questions about variations that I'm wondering if anyone has done. (I did not find any examples of these variations elsewhere).

    1) In this variation, you have the photon pass through the slits twice. First through a single slit, then through a double slit. My thought is that a single slit, according to my understanding of other experiments, causes the collapse of the wave function, "forcing" the photon to a particle. If it's a particle, then does it go through only 1 of the 2 remaining slits? Or does its wave form "reconstitute" and the same interference pattern is observed?

    2) In this variation, a divider or barrier is placed between the two slits - thus theoretically preventing interference. In this case, is an interference pattern observed? Is any pattern observed?

    Thanks for your thoughts.
  2. jcsd
  3. Aug 3, 2009 #2


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    1) That does not really change anything.

    2) No interference because you know which slit it went through - or could know. That eliminates the the interference effects.
  4. Aug 3, 2009 #3
    I assume that means the experiment would show an interference pattern (implying that the photon went from particle to wave somewhere along the way).

    I guess I'm having trouble with this. My understanding (or "interpretation") is that the interference pattern is a result of a wave passing through both slits and interfering with itself. If that's the case, then there would be no concept of "which slit", since it would always be "both slits". But I would expect no interference because the wave would still not be able to interfere with itself due to the barrier.

    What I'm curious about is whether such experiments have actually been performed.
  5. Aug 3, 2009 #4


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    1. Having it go through a single slit does not turn it into a "particle".

    2. A barrier cutting the apparatus into 2 chambers will eliminate the signature interference effects, as you say. This is the kind of experiment that is usually done in physics labs, not sure I can put a finger on a specific reference. All kinds of objects have been run through double slit setups, not just light. With proper slit size and other parameters, they all show interference. This demonstrates that even matter has both wave and particle properties.
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