Can a future choice affect a past measurement's outcome?

Yakir Aharonov, Eliahu Cohen*, Avshalom C. Elitzur

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


An EPR experiment is studied where each particle within the entangled pair undergoes a few weak measurements (WMs) along some pre-set spin orientations, with the outcomes individually recorded. Then the particle undergoes one strong measurement along an orientation chosen at the last moment. Bell-inequality violation is expected between the two final measurements within each EPR pair. At the same time, statistical agreement is expected between these strong measurements and the earlier weak ones performed on that pair. A contradiction seemingly ensues: (i) Bell's theorem forbids spin values to exist prior to the choice of the orientation measured; (ii) A weak measurement is not supposed to determine the outcome of a successive strong one; and indeed (iii) Almost no disentanglement is inflicted by the WMs; and yet (iv) The outcomes of weak measurements statistically agree with those of the strong ones, suggesting the existence of pre-determined values, in contradiction with (i). Although the conflict can be solved by mere mitigation of the above restrictions, the most reasonable resolution seems to be that of the Two-State-Vector Formalism (TSVF), namely, that the choice of the experimenter has been encrypted within the weak measurement's outcomes, even before the experimenters themselves know what their choice will be.

Original languageEnglish
Pages (from-to)258-268
Number of pages11
JournalAnnals of Physics
StatePublished - 1 Apr 2015


FundersFunder number
Israel Science Foundation1311/14


    • Quantum nonlocality
    • Two-State-Vector-Formalism
    • Weak measurement


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