Making Mistakes Saves the Single Observer’s World of the Extended Wigner’s Friend Experiment

Abstract

The Extended Wigner’s Friend thought experiment, comprising a quantum system containing an agent who draws conclusions upon observing the outcome of a measurement of a quantum state prepared in two nonorthogonal versions by another agent, led its authors to conclude that quantum theory cannot consistently describe the use of itself. It has also been proposed that this thought experiment is equivalent to entangled state (Bell-type) experiments. It is argued in this paper that the assumption of the freedom of choice of the first Wigner’s friend regarding how to prepare a quantum state in one of the two available nonorthogonal versions invalidates such equivalence.