Bell-inequality violation and relativity of pre- and postselection

Abstract

The Bell inequalities can be violated by postselecting on the results of a measurement of the Bell states. If information about the original state preparation is available, we point out how the violation can be reproduced classically by postselecting on the basis of this information. We thus propose a variant of existing experiments that rules out such alternative explanations by having the preparation and the postselection at spacelike separation. Unlike the timelike case in which one can sharply distinguish Bell inequality violations based on pre- or postselection of a Bell state, in our scenario the distinction between these physical effects becomes foliation dependent. We call this ``relativity of pre- and postselection'' and conclude from it that quantum state evolution is not a fundamental process and that we should adopt an event-based Heisenbergian picture instead.