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B Double slit question

  1. Aug 12, 2017 #1
    Apologies if this is a ridiculous question (I have zero scientific education). I recently watch a video about retrocausality and thought that this may be an explanation for the wave properties of a single photon fired in the double slit experiment. My scientific ignorance will be on full show here but as far as I'm aware this test always requires massive quantities of photons to be fired from the same location so if retrocausality is true the reason for the wave properties of a single photon is because it is interacting with the photons from the subsequent photons fired in the experiment.
    Last edited by a moderator: Aug 12, 2017
  2. jcsd
  3. Aug 12, 2017 #2


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    Retrocausality has no particular relationship to double slit interference. Such interference is unrelated to past or future particles, as you can do the test 1 photon at a time and still build up a pattern.
  4. Aug 12, 2017 #3
    Exactly...one photon at a 'time'...if you remove 'time' from the equation then all of the photons in the experiment are fired together..and therefore interact with each other
  5. Aug 12, 2017 #4


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    Retrocausality is neither needed nor especially helpful to explain why the interference pattern appears. The quantum mechanical description of a single particle says that we should expect an interference pattern if we fire enough single particles at the screen and that it is caused by self-interference... so no retrocausality needed.

    If you can get hold of the book "Sneaking a look at god's cards" by Giancarlo Ghirardi, you may find that it's a better use of your time than watching videos - many of the online videos are pretty much garbage, and there's no reliable way of telling the good ones from the bad.
  6. Aug 12, 2017 #5
    To me (as a layman) your statement agrees with my premise because you included 'if' ie "The quantum mechanical description of a single particle says that we should expect an interference pattern if we fire enough single particles at the screen". Has there been any studies that state that if you don't fire a large amount of particles at a screen you would get the same result?
  7. Aug 12, 2017 #6


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    The interference pattern builds up one dot at a time, so of course no intereference pattern will be observed if you only send a single particle through - you'll get a single dot somewhere on the screen. However, when we do send multiple particles through, the statistical distribution of the dots is independent of the number of particles. This result is consistent with the quantum mechanical explanation and inconsistent with any theory in which the behavior of any given particle is affected by the total number of particles, whether from the future or not. Thus, the answer to your question ("Has there been any studies that state....?") is "Yes, pretty much all of them".

    Another problem is that the calculations that explain the interference pattern through self-interference are the same ones that explain chemical bonds (and hence just about all of chemistry), semiconductors (and hence just about all of modern electronics), just about all of solid state physics, and a bunch of other stuff that I'm forgetting right now. An explanation of the double slit experiment that cannot be extended to these other cases is no explanation at all.

    However, this discussion is now well on the wrong side of the Physics Forums rule prohibiting personal theories and speculation. If you want to know what quantum mechanics does say... Ask away. That's what we're here for. But discussion of alternative theories, unless published in an appropriate peer-reviewed journal, is off-limits.
    Last edited: Aug 12, 2017
  8. Aug 13, 2017 #7
    It is more likely that the particle is the source of the wave and it interferes with itself via its wave. Essentially the pilot wave theory.

    This example is seen in fluid dynamics with silicon oil droplets as the particle.

    This is the only deterministic explanation that I know of. The issue is that it cannot be tested on particles because we would need to know their position when they exit the laser.
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