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Double Slit/Photo Detection/Is it the SAME photon?

  1. Dec 7, 2009 #1
    I was reading about the double slit experiment (it seems I always glean a better understanding every time I read, which shows how little I really get it in the first place), and I was wondering:
    Is there some way for us to know that the photo that was fired (given a single photo experiment) is actually the SAME photo that hits the screen?
    Perhaps I don't have a proper understanding of what photos are - if this is the case let me know.
    But if I remember photons are absorbed and re-emitted all the time, right? Like light hits something and if it bumps and electron around then a photon is released?

    If that is the case I don't see how you could say that the photon(s) that hit(s) the screen is/are actually the same one(s) that was/were fired if there are say... air particles, and and dust and whatever, not to mention some piece of plastic or metal to supply the slits...

    Do I have a proper understanding? Close? Or do I totally not get it at all?
  2. jcsd
  3. Dec 7, 2009 #2


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    You should probably read this, post #4: https://www.physicsforums.com/showthread.php?t=104715

    Basically, your idea wouldn't make sense on a number of levels. For example, if you have a vacuum chamber there won't be air or dust. And the double slit experiment is not about the medium, it is about interference (usually self-interference).

    As to whether it is the same photon or not: some of that answer is pholosophical/semantic. What is "the same"? Indistinguishable? Or do you imagine that every photon is unique and could conceptually be tracked in its travels? There are complicated issues in many ways, but the usual answer is: YES, it is the same particle.
  4. Dec 7, 2009 #3
    Thanks, I'll read that link and post again when I've understood photons a bit better:P
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