Is the past (and future) there when nobody looks? (IMAGE)

University of Vienna

Is the past (and future) there when nobody looks?

Caption

An observer (Wigner's friend) performs a quantum measurement on a spin system. Later, Wigner measures the friend and spin in an entangled basis. As a consequence of this measurement, not only does the friend not reliably remember his past observed outcome, but cannot even quantify this ignorance with a reasonably behaved probability distribution.

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© Aloop, IQOQI-Wien, Österreichische Akademie der Wissenschaften

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