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Problem with the two-slit experiment

  1. Sep 2, 2012 #1
    The test should have been done within a vacuum. The interference of air molecules in earth's atmosphere obviously causes an unwanted result, thus making the test results improbable. I don't know much about Quantum Physics, but I do understand how tests are supposed to be conducted, without any unwanted variables.

    Again, I said I don't know much about Quantum Physics, but is it a possibility that photons travelling through air molecules will cause the air molecule to travel along the path of the photon wave and hit the monitor as a particle, yet develop into the pattern of a wave?
  2. jcsd
  3. Sep 2, 2012 #2


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    Do you have a source that says the two slit experiment is not done in a vacuum?
  4. Sep 2, 2012 #3
    Well it's difficult to find Tanamura's original procedure anywhere, but I'm fairly certain that all variations of the double-slit experiment were done on earth.
  5. Sep 2, 2012 #4


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    So, are you refuting the existence of vacuum chambers on Earth, or are you unsatisfied with their quality?
  6. Sep 2, 2012 #5
    Air molecules are subject to the laws of Quantum Mechanics.
  7. Sep 2, 2012 #6
    Were there any double-slit experiments done inside of a vacuum chamber?
  8. Sep 2, 2012 #7
    Pinoasis, the effect of the atmosphere is well-understood, and plenty of experiments have been done in vacuum chambers. For photons, air doesn't have much effect at all: after all, the fact that air is transparent is just the fact that photons pass through air without being affected. For double slit experiments with electrons and larger particles, the experiment must be conducted in a vacuum, because electrons do interact with air molecules. In a perfect vacuum, you get a regular interference pattern. As the vacuum becomes less perfect, the interference pattern gradually goes away. You can think of this as a result of air molecules interacting with the electron, and thus "observing" which path the electron took through the slits. And when something observes which path the electron took, there's no interference pattern.

    To be clear, air molecules tend to *destroy* the interference pattern, they do not create it.
  9. Sep 4, 2012 #8


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    No, that is not possible. There is a simple rule for determining whether there is interference or not. That rule is whether or not it is possible, in principle, to determine which slit the particle passes through. If you could know, there will be no interference.

    There are ways to vary the knowledge we have of the "which slit" info continuously. Keep in mind that the interference pattern can theoretically vary from 0% to 100% (perfect case of course). The easiest example of that is to place polarizers in front of each slit. When they are crossed, there is no interference. When parallel, there is. Angles in between 0 and 90 degrees yield less more or less interference according to the cos^2 rule. So that is the primary factor.

    As previously mentioned by The_Duck, the presence of air has an extremely slight tendency to reduce the amount of interference in the pattern. So maybe air reduces it from 95.0% to 94.9% or something like that. Not enough to bother with in an experimental situation. It is NOT required that all variables be eliminated in an experimental situation, it is sufficient that they are controlled or minimized.

    Of course, you are free to ignore experiments that do not meet your own standards. However: If you reject the double slit, then you may as well also reject every experiment ever done.
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