Undoing Quantum Measurement: Novel Twists to the Physical Account of Time

Since quantum measurement remains so ill-understood, its time-reversed ver-sion is bound to offer new insights. If undoing a quantum measurement is impossible in principle, it bears on the old problem concerning the origin of irreversibility. If it is possible, it gives new twists to basic notions like inde-terminism and the uncertainty principle. We demonstrate this approach on the time-reversed version of the EPR experiment, where two entangled par-ticles undergo measurements followed by ”unmeasurements. ” Whereas Bell’s theorem rules out local hidden variables, our experiment yields a complemen-tary proof that even nonlocal hidden variables lead to observed violations of relativity. We are therefore left with either genuine randomness or a subtle time-asymmetry at the basis of quantum phenomena. Both options render the relativistic account of time incomplete. Genuine emergence and novelty turn out to be the most fundamental characteristics of physical reality