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Hypothesis: Can a photon be predicted where it will hit?

  1. Feb 12, 2015 #1
    Hi Scholars!


    The two slit experiment is like studying the fundamentals of Quantum Physics. Anyway, on the two slit experiment, where individual photons are fire one at a time on the 1st screen that has two slits. The photons would either go through both slits, or through the left slit or through the right slit.


    On the second screen, it's like a photographic plate that captures light. Well, when hundreds of photons have gone through the first screen, the photon goes on to hit on the second screen where eventually an interference pattern will emerge. The photons hits randomly on the second screen but interference still appears.


    100% accuracy can be calculated in a group of photon distribution. Hence, using the equation: x=(m * w * L) / d. x=position, m=order, w=wavelength, L=distance between screens, d=separation of slits. This equation is utilized to find out how far apart are bright fringes from the center bright fringe. However, it cannot be done for an individual photon.


    Now, if someone could predict the future hits on the second screen. What would be the ramifications? It's only a hypothesis but what would happen if this could be done without disturbing the interference pattern. Would that change current theories?


    Sincerely,

    Arthur Hernandez
     
  2. jcsd
  3. Feb 12, 2015 #2

    phinds

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    You are asking "if physical laws did not apply, what would physical laws say about <insert nonsense of your choice>"
     
  4. Feb 13, 2015 #3

    bhobba

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    QM would be dethroned.

    Thanks
    Bill
     
  5. Feb 22, 2015 #4
    Surely this is perfectly possible to do using entangled photons without dethroning QM?
     
  6. Feb 22, 2015 #5

    phinds

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    Why do you think bhobba is wrong about that and you are right? Do you know something he doesn't? If so, please state what it is and explain how such a prediction (as discussed in the OP) would not violate QM.
     
  7. Feb 22, 2015 #6
    It's perfectly possible that bobba overlooked the use of entangled photons and was only thinking of the single particle case. It's also possible I'm wrong - that's why I asked a question rather than making a bald assertion. It would be best to let him answer for himself.
     
  8. Feb 23, 2015 #7

    bhobba

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    I am perfectly aware of such things.

    It would be dethroned from the very axioms QM is based on:
    https://www.physicsforums.com/threads/the-born-rule-in-many-worlds.763139/page-7

    See post 137

    Notice the key axiom:
    An observation/measurement with possible outcomes i = 1, 2, 3 ..... is described by a POVM Ei such that the probability of outcome i is determined by Ei, and only by Ei, in particular it does not depend on what POVM it is part of..

    See that key word highlighted. If you could predict the outcome then probability wouldn't enter into it and the axiom would be invalidated and replaced with something else. It may still be valid as some kind of approximation but it would be wrong.

    Thanks
    Bill
     
  9. Feb 23, 2015 #8
    Thanks for the link.

    Well, you said to a fellow mathematician that there is a "lot to digest". And so there is, even more so for someone like me who struggles with maths. (I'm working on it - give me time!) I don't have any feel at all for POVMs so I'm not sure whether "in particular it does not depend on what POVM it is part of" is key to the question. If it is perhaps you could say what it means in this specific example?

    But we may get there quicker if I just comment on this: "If you could predict the outcome then probability wouldn't enter into it". In my scenario, the first photon is already subject to probability. It hits the screen at a certain, though not predictable, position. If my understanding of entanglement is correct then its partner must hit the other screen in a corresponding place. There doesn't seem to be any denial of probability in this - the pair of particles is subject to the same probability distribution because they are entangled. The fact that the second measurement yields the same positional outcome using a different photon does not undermine the probability principle any more than finding a single electron in the same place twice in quick succession would do.

    Whether my understanding of entanglement is correct is another matter.
     
  10. Feb 23, 2015 #9

    bhobba

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    Please detail that understanding and its applicability to the double slit experiment.

    When doing that please take into account forum rules that personal speculative theories are off topic here.

    Each position measurement in that experiment is independent and nothing to do with entanglement.

    Thanks
    Bill
     
  11. Feb 23, 2015 #10

    bhobba

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    The precise detail isn't the point - don't worry if you don't get the specifics.

    The point is right at its foundations QM is probabilistic. If it wasn't and you could actually predict the outcomes of observations such as the position in the double slit experiment, then like classical thermodynamics is to classical mechanics, it would not be a fundamental theory any-more and it would be dethroned.

    Thanks
    Bill
     
  12. Feb 23, 2015 #11
    I was not suggesting that probability can be suspended. What I was suggesting is that probability applies to an entangled pair as a whole so that although the position of the first is probabalistic, that of the second correlates precisely with the first.

    But in any case, I've realized where I was going wrong. I was misled by the emphasis on knowing where the second photon will land - which is somewhat suggested by the title of the thread! - and was overlooking the importance of retaining the diffraction pattern. If the OP had been asking just about predicting the position, my idea would have stood, but on thinking about it I'm pretty sure you can't create a diffraction pattern *and* retain the positional entanglement.
     
  13. Feb 23, 2015 #12

    bhobba

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    What entangled pair?

    The double slit has no entangled pair and I specifically mentioned that in my reply.

    I have zero idea why you are still going down that path.

    Thanks
    Bill
     
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