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Detection loophole vs. Spooky action at a distance

  1. Sep 12, 2012 #1
    Hello everybody,

    I was wondering: why is "spooky action at a distance" considered to be more likely than a detection loophole? That is to say, why is Bell's Theorem assumed to imply that two entangled particles must communicate faster than light, rather than saying that a subset of particles is not measured at all?

    I was considering the detection loophole, and if the detection loophole would exist it would seem likely that the number of measured entangled photons per second would vary based on the relative angle of two detectors. Has such an experiment been done to confirm or refute it? (And if so, let me guess, it refuted it?)
    If so, do you have a link to such an experiment?

    Thanks in advance,
  2. jcsd
  3. Sep 12, 2012 #2


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    The relative angle between is itself non-local. So you are back to spooky action at a distance if you hypothesize that as the source of the violations.

    On the other hand, if there is a detection issue it means that QM is flat out wrong in predicting the cos^2(theta) relationship. So in preserving locality, you must throw out QM - which of course makes accurate predictions. And you must add a new, previously unknown quantum effect - detection discrimination. In other words, for the detection loophole be useful, there must be discrimination in the detection of pairs which is skewed towards the (wrong) QM predictions! Ie there must be unfair sampling, that is the assumption behind the detection loophole.
  4. Sep 12, 2012 #3
    Indeed, my curiosity leads me to wonder whether QM is only a specific subset of reality. There seem to be loopholes in every experiment that proves quantum mechanics, and it seems, though I'm no expert, that such loopholes may be innate to the theory of QM.
    I don't dismiss QM. I just wonder about a broader reality, of which part could potentially be unmeasurable.

    What I meant by the angle between two detectors effecting the number of measured photons does not necessarily require spooky action at a distance. Imagine a photon for which "measuring it" (eg. setting the polarization filter to that angle) for half of the area will make the photon disappear, similar to a photon interfering with itself in the double slit experiment.
    If we have an entangled pair of such a photon and we measure at a relative angle of 90 degrees, then the chance that at least one of those photons disappears is 75%. At an angle of 0 degrees, the chance that at least one photons disappears is 50%. And if either of them disappears and is not measured, measurement is not taken into account as a pair of entangled particles (at least in the CHSH experiment), and as a result is not taken into consideration for the correlation.
    I know that this does not in any way reflect QM, but it shows that it is not impossible that the relative angle of the detectors may affect the number of particles measured without spooky action at a distance.

    After posting this I did find an article which explains a similar concept (though similarly flawed in many ways), showing how such a detection loophole may cause this. It went on about CH74, which apparently does not suffer from a detection loophole. The only loophole possible there is apparently the "enhancement loophole", or a violation of the "no-enhancement assumption".

    So both questions still stands, but the first one becomes: why is it considered more likely that spooky action at a distance can indeed happen, than that a detection/enhancement loophole exist? I find the latter a lot more intuitive.

    And also, does the speed of the interval between measured entangled particles vary for different relative detector angles, or the removal of one or both polarizers? What experiments have been done regarding this?

    Again: I do not reject or embrace QM as the full reality. I believe QM is definitely an extremely important subset of reality, but I wish to explore any potential more intuitive explanations before I accept QM as the full reality.

    Thanks for your answer!
  5. Sep 12, 2012 #4


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    You will find that your example will not work. It will not yield results which match actual experiments. Keep in mind that the results of the subsample must match the QM prediction while the full universe does not.

    There is a computer simulation from the de Raedt Michelsen et al group which does come pretty close. It is quite complex to discuss and beyond the scope of this thread. You may be interested in reading it though.

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