Uncomfortable bedfellows: Objective quantum Bayesianism and the von Neumann–Lüders projection postulate

In this paper I critically evaluate the justification of the von Neumann–Lüders projection postulate for state changes in projective measurement contexts from the objective quantum Bayesian perspective. I point out that the justification provided so far for the von Neumann–Lüders projection postulate is insufficient. I argue that the best way to correct this problem is to make an assumption, Benign Realism, which is contradictory to the objective quantum Bayesian interpretation of quantum states.

► Bayesian justification of the von Neumann–Lüders projection postulate is examined.
► Justification is insufficient and cannot be made sufficient for objective Bayesians.
► Benign Realism, contradictory to Bayesianism, is required for justification