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2 slit experiment, what happen with 3,4,5 ?

  1. Jun 25, 2012 #1
    it's all in the question, but i'll elaborate o:) the scientists shot one photon each time and discover it moves through both slits, i wanna know, does the photon "divide" to countless particles or just 2? do the scientists tried the experiment with more than 2 slits?
    thanks :rofl:
  2. jcsd
  3. Jun 25, 2012 #2
    I don't think "divide" would be the proper word, but, thinking along similar lines, it will take countless paths given countless slits. You just have to keep on adding the amplitudes for any number of slits and as the number of slits approaches infinity you get Feynman's path integral! I strongly recommend you to go through three or four pages of "QFT in a Nutshell" by Anthony Zee, starting from page 7 onwards, that is, the first few pages of Chapter I.2. You will get the first couple of those few pages for free here:

  4. Jun 25, 2012 #3


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    This doesn't just happen for 'slits'. It happens for everything that light (in fact, all EM waves) bounces off or passes through; the phenomenon, in general, is called Diffraction and two slit interference is just the simplest example. A single photon will end up being detected at just one point in space. One way of looking at this is to say it has been spread 'everywhere' that the classical wave model would have put the wave but that it only turns up in one place. The result of a large number of photons is precisely what the classical wave model would predict. This is the 'duality' idea at work and you have to take both ideas on board at once. You can't just choose one or the other.
  5. Jun 25, 2012 #4

    Chi Meson

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    Problems arise when you try to mentally "picture" what happens at the quantum level. We can't see what the photon does because we can't see a photon (although we can detect the absorption of photons when they hit our retinas, etc).

    Our brains have no experience with observing the behavior of fundamental particles. You need to get used to the fact that every analogy we come up with to model these particles is flawed in some way.

    So we end up saying things like what you read above. It's the best we can do to picture what is going on. Mathematics, however, allows us to be precise and when we mathematically predict the outcome of even complicated arrangements, we find that our understanding is supported by solid, repeatable, and durable evidence.
  6. Jun 25, 2012 #5

    Andy Resnick

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    Conceptually there's not much new, the situation can be easily generalized to an arbitrary number of slits using concepts from signal processing- the interference pattern is the Fourier transform of the 'mask': for example, two slits, each of width 'd' and separated by distance 'a' can be written as rect(x/d) * δ(x +/- a), and the far-field diffraction pattern is then [sinc(d*s)][cos(s/a)], where 's' is the conjugate variable to 'x'.

    Going to multiple slits is then fairly trivial- even the limit where the number of slits goes to infinity and the slit width and spacing go to zero.
  7. Jun 25, 2012 #6
    1. thank you all for anwering me :)
    2. specific the quote: but "wave" is a term from macro world. and math applied on models we create, after imagining them in our minds we can wrap it with math, no?!
  8. Jun 25, 2012 #7


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    Bazillions of times, at least in classical optics. It's a common undergraduate lab experiment.


    I don't think the QM treatment and conceptual problems with single photons are any different in these cases than with two slits.
  9. Jun 25, 2012 #8


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    Every time you open your eyes you are doing that. You are producing a diffraction pattern of what's out there on your retina. At that scale, light is behaving 'very' classically and the diffraction pattern is what you get with ray tracing but only because your pupil is large enough.
    A so-called diffraction grating uses many slits and the pattern it produces has very wide spaced maxima and each 'order' spreads out the light into the spectrum of wavelengths.

    Then there is the hologram - again, it's a diffraction pattern of an object and this time the object is in three dimensions.
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