Some remarks on knowledge and probability arising from counterfactual quantum effects (Q2738521)

Can the mere possibility of a physical phenomenon affect the outcome of an experiment? In fact quantum theory presents us actual physical effects arising from ``counterfactuals'', that is physical effects brought about by things that might have happened, although they did not happen. How can that be? After a short outline of the quantum-mechanical description of physical reality, the occurrence of such counterfactual effects in quantum theory is illustrated by means of a Mach-Zehnder interferometer. Then these paradoxical phenomena undermining the very notion of physical event and questioning as to what knowledge of physical reality can ever be obtained will be analysed using a classical possible-worlds model of knowledge and probability. Finally, a surprising application of counterfactual quantum effects producing a new kind of computing with no classical analogue will be shown.NEWLINENEWLINEFor the entire collection see [Zbl 0956.00050].