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Double slit experiment with electrons

  1. Apr 9, 2013 #1
    I often read that electrons that pass through two small openings in a wall will land on a back screen and make a pattern as if the electron were a wave. But if we look at the electrons the distribution on the screen is as if the electrons are particles. What does it mean to "look at the electrons"? Would it be more accurate to say "if the electrons interact with photons"? Or am I missing something?

  2. jcsd
  3. Apr 9, 2013 #2


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    ANY interaction that would allow knowledge of which slit the electron went through destroys the interference and basically forces the electron to act like a particle instead of a wave. Google the "double slit experiment". It's a quantum-mechanics thing.
  4. Apr 9, 2013 #3
    I find this video to, if not explain, then at least illustrate the double slit experiment in a way that should be easy to understand.

    Last edited by a moderator: Sep 25, 2014
  5. Apr 10, 2013 #4
    Have any of you read this:

    http://philosophyfaculty.ucsd.edu/faculty/wuthrich/philphys/EllermanDavid2012Man_QuantumEraser2.pdf [Broken]

    It is basially saying the methods for detecting is the cause of the collapse of the wave function. I have also read about the experiment by Aephraim Steinberg of the University of Toronto in Canada. They used "weak measurements" which seams to support this idea. Opinions?
    Last edited by a moderator: May 6, 2017
  6. Apr 11, 2013 #5
    So it is not electron - photon interaction that determines the distribution pattern. Rather, it is only if this interaction gives us knowledge? I imagine that running the experiment under a regularly lighted room would have no effect (the electron distribution will remain as a wave). Is it even possible to use photons to detect which slit the electron goes through (I have been assuming this is true, but I'm not sure)? If it is possible, could the same type of photon (that is, the same photon produced in a regularly lighted room) be used to detect which slit the electron goes through, thereby creating a distribution pattern resembling a wave?
  7. Apr 11, 2013 #6
    as phinds said, not just gives us knowledge, but could give us knowledge. If you want the really get into what that means, you're going to have to do some math. Without that, it can be difficult (sometimes even with that) to be sure what will "collapse" the wavefunction and what will not.

    I don't get the last part of your question, but suffice it to say, if you, or anyone else, could record the information about which slit the particle passes through, there will not be interference.
  8. Apr 12, 2013 #7
    Is it possible to have an experiment, say experiment 1, where photons interact with electrons in such a way that does not give us knowledge, resulting in a distribution pattern resembling a wave?

    AND conduct an experiment, say experiment 2, where the same type of photons (same frequencies as in experiment 1) interact with electrons in such a way that DOES give us knowledge, resulting in a distribution pattern resembling a particle?
  9. Apr 12, 2013 #8

    Claude Bile

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    "Look at the electrons" in this context means "perturb the phase of the electronic wavefunction" through (for example) scattering of a photon.

    This interaction affects (destroys?) the coherence of the electronic wavefunction. i.e. there is no longer a definitive phase relation between the wavefunction at each slit; which "kills" the interference pattern.

  10. Apr 13, 2013 #9
    Thank you! I was hoping for an answer that indicated some sort of physical interaction with the electron that determined the distribution pattern.
  11. Apr 14, 2013 #10
    So to make sure I understand correctly, it is interactions that perturb the phase of the electron wavefunction such that the interference pattern is affected (or removed) that is responsible for the phenomenon. If that is the case then why do I always see some business about information (or the potential for it) being some sort of magical ingredient that kills the interference pattern? I mean, true, you can draw information from whatever interaction led to the perturbation but it is not the fact that you could have drawn information from the interaction that killed the pattern, rather it was the interaction itself that did it. My point being that the physics cares not about your gathering of information, but actually cares about the perturbation itself.

    If the above is correct, then I wish those speaking about the double slit experiment would be more clear about that, and really step off the gas about 'information'. It not only confused me in terms of the physics, but it leads to many laymen introducing their woo-woo pseudoscience about our consciousness' gathering of information affecting the final outcome (sorry this last bit is a pet peeve of mine).

    If the above is not correct then I apologize, and would like being corrected.
  12. Apr 14, 2013 #11


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    Perturbing, in the normal sense of the word, does not make the difference!

    The classic example of this is placing something like spin or polarization filters in front of each of the slits. When their relative orientation changes, the pattern changes. That is because the potential for determine which slit information is gained or lost. But presumably the filters are just as active either way.
  13. Apr 24, 2013 #12
  14. Apr 25, 2013 #13
    I think the central idea we are converging towards is entanglement. A key element of quantum mechanics, with the combination of the Heisenberg uncertainty principle, I can state that its not sufficient to describe the double/single slit exp. using classical analogies, we require rigorous math and a little thing called axiomatic quantum mechanics.

    ''What does it mean to "look at the electrons"? Would it be more accurate to say "if the electrons interact with photons"? Or am I missing something?'' Kjamha.

    What your missing is entanglement... even Einstein got a little frustrated by this.
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