On the objectivity of measurement outcomes

TL;DR

This paper critiques recent quantum measurement arguments involving Wigner's friend scenarios, showing they rely on mistaken assumptions about correlations, and clarifies that measurement outcomes can still be considered objective.

Contribution

It identifies and corrects faulty assumptions in recent no-go theorems, demonstrating the objectivity of measurement outcomes using explicit pilot-wave theory calculations.

Findings

Faulty assumptions about correlations invalidate recent no-go theorems.

Objectivity of measurement outcomes remains consistent with quantum predictions.

Locality assumptions weaken the force of certain no-go theorems.

Abstract

Recent arguments, involving entangled systems shared by sets of Wigner's friend arrangements, allegedly show that the assumption that the experiments performed by the friends yield definite outcomes, is incompatible with quantum predictions. From this, it is concluded that the results of measurements cannot be thought of as being actual or objective. Here, I show that these arguments depend upon a mistaken assumption, regarding the ("mixed") correlations between the results of the friends and those of "the Wigners", which leads to invalid predictions. It is not, then, that the assumption of definite outcomes leads to trouble, but that the results derived with such an assumption are contrasted with faulty predictions. Next, I explore the more famous no-go theorems by Frauchiger and Renner and by Brukner, on which these recent arguments are motivated. Regarding the first, I show that, although it is cast in a different form, it also rests on the mistaken assumption regarding "mixed" correlations--rendering it invalid. Regarding Brukner's theorem, I point out that it depends on the quite unattractive assumption of locality, a fact that fully diminishes its force. Throughout, I illustrate my claims with explicit calculations within pilot-wave theory.