Causality Is Just a Point of View

Quantum decision affects results of measurements taken earlier in time:

Due to the 104-meter fiber-optic cable, Victor’s measurements occurred at least 14 billionths of a second after those of Alice and Bob, precluding the idea that the setting of the BiSA caused the polarization results to change. While comparatively few photons made it all the way through every step of the experiment, this is due to the difficulty of measurements with so few photons, rather than a problem with the results. 

Ma et al. found to a high degree of confidence that when Victor selected entanglement, Alice and Bob found correlated photon polarizations. This didn’t happen when Victor left the photons alone.

Suffice it to say that facile explanations about information passing between Alice’s and Bob’s photons lead to violations of causality, since Alice and Bob perform their polarization measurement before Victor makes his choice about whether to entangle his photons or not. (Similarly, if you think that all the photons come from a single laser source, they must be correlated from the start, and you must answer how they “know” what Victor is going to do before he does it.) 

The picture certainly looks like future events influence the past, a view any right-minded physicist would reject. …

Nevertheless, this experiment provides a realization of one of the fundamental paradoxes of quantum mechanics: that measurements taken at different points in space and time appear to affect each other, even though there is no mechanism that allows information to travel between them.

My brain hurts.

(Note that Alice, Bob, and Victor are not actual people but mechanisms.)

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3 Responses to Causality Is Just a Point of View

  1. Frank says:

    Score one for determinism. One big block of time. What a relief.

  2. Earl Killian says:

    Alice, Bob, and Victor are standardized names in the crypto world:
    (along with Eve, Mallory, and others…)

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