mercredi 28 août 2013

Retrocausality and the two-state vector formalism

I am interested in our resident physicists' opinions on this paper titled "Can a Future Choice Affect a Past Measurement's Outcome?"



http://arxiv.org/abs/1206.6224



The summary:



"An EPR experiment is studied where each particle undergoes a few weak measurements along some pre-set spin orientations, whose outcomes are individually recorded. Then the particle undergoes a strong measurement along a spin orientation freely chosen at the last moment. Bell-inequality violation is expected between the two final strong measurements within each EPR pair. At the same time, agreement is expected between these measurements and the earlier weak ones within the pair. A contradiction thereby ensues: i) Bell's theorem forbids spin values to exist prior to the choice of the spin-orientation to be measured; ii) A weak measurement cannot determine the outcome of a successive strong one; and iii) Indeed no disentanglement is inflicted by the weak measurements; yet iv) The weak measurements’ outcomes agree with those of the strong ones. The most reasonable resolution seems to be that of the Two-State-Vector Formalism, namely, that the experimenter’s choice has been encrypted within the weak measurement's outcomes, even before the experimenter themselves knows what their choice will be. Causal loops are avoided by this anticipation remaining encrypted until the final outcomes enable to decipher it."



I find the final paragraph both interesting and puzzling:



"Finally, this experiment sheds a new light on the age-old question of free will. Apparently, a measurement's anticipation of a human choice made much later renders the choice fully deterministic, bound by earlier causes. One profound result, however, shows that this is not the case. The choice anticipated by the weak outcomes can become known only after that choice is actually made. This inaccessibility, which prevents causal paradoxes like “killing one's grandfather,” secures human choice full freedom from both past and future constraints. A rigorous proof for this compatibility between TSVF and free choice is given elsewhere in detail [8]."



Here is another paper written for a more general audience:



http://arxiv.org/abs/1307.7744



~~ Paul





via JREF Forum http://forums.randi.org/showthread.php?t=264464&goto=newpost

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