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I Cosmic Bell Test

  1. Nov 22, 2016 #1

    DrChinese

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    You gotta love this! A top experimental team was assembled to test the "freedom of choice" loophole (if you can call it that). Usually, when random settings are needed in a Bell test, a computer generated value is obtained (pseudo random), or similar. This is relatively "local", and subject to the assertion that something is preventing free choice of settings for the Bell test. In this clever version, light from distant stars is used as an input to select setting values. Then a Bell test is performed. Check it out:

    https://arxiv.org/abs/1611.06985

    Bell's theorem states that some predictions of quantum mechanics cannot be reproduced by a local-realist theory. That conflict is expressed by Bell's inequality, which is usually derived under the assumption that there are no statistical correlations between the choices of measurement settings and anything else that can causally affect the measurement outcomes. In previous experiments, this "freedom of choice" was addressed by ensuring that selection of measurement settings via conventional "quantum random number generators" (QRNGs) was space-like separated from the entangled particle creation. This, however, left open the possibility that an unknown cause affected both the setting choices and measurement outcomes as recently as mere microseconds before each experimental trial. Here we report on a new experimental test of Bell's inequality that, for the first time, uses distant astronomical sources as "cosmic setting generators." In our tests with polarization-entangled photons, measurement settings were chosen using real-time observations of Milky Way stars while simultaneously ensuring locality. We observe statistically significant ≳11.7σ and ≳13.8σ violations of Bell's inequality with estimated p-values of ≲7.4×10−32 and ≲1.1×10−43, respectively, thereby pushing back by ∼600 years the most recent time by which any local-realist influences could have engineered the observed Bell violation.
     
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  3. Nov 22, 2016 #2

    ShayanJ

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    Interesting! Today I was explaining to my friends how superdeterminism is something you can't experimentally rule out. Turns out you can! Kudos to experimentalists.
     
  4. Nov 22, 2016 #3

    Demystifier

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    No you can't. At best, you can rule out some special types of superdeterminism, but not superdeterminism in general. In this case, possible superdeterminism is pushed back 600 years ago.
     
  5. Nov 22, 2016 #4

    ShayanJ

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    Yeah, strictly speaking, only local superdeterministic theories are ruled out. But the whole point of superdeterminism was to preserve both locality and classical reality.
     
  6. Nov 22, 2016 #5

    Nugatory

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    Nope... All this experiment can do is establish a new upper bound on its plausibility.
    Not by this experiment. The past light cone of the distant stars and the experimental apparatus still overlap, so the correlation could be the deterministic result of events in that area of overlap. Of course, that requires the implausible hypothesis that some random atomic collision millennia ago has completely determined the emission of the light that reaches the experimenter from a far-distant star and also the exact behavior of the device creating the entangled pairs.... So we have a new upper bound on the plausibility.
     
    Last edited: Nov 22, 2016
  7. Nov 22, 2016 #6

    Demystifier

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    No they are not. According to this experiment, local superdeterministioc causes that happened more than 600 years ago are not ruled out.
     
  8. Nov 22, 2016 #7

    ShayanJ

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    So I misinterpreted that 600 years!
    Thanks for the clarification.
     
  9. Nov 22, 2016 #8

    DrChinese

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    It also leaves open the "Last Thursdayism" loophole. :smile: In case anyone is disappointed that Bell test loopholes are being tightened or closed.
     
  10. Nov 22, 2016 #9

    Demystifier

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    Or my favored one: the-world-is-local-but-we-are-too-stupid-to-understand-how loophole.
     
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