The original Wigner's friend paradox within a realist toy model

TL;DR

This paper presents a classical toy model that reproduces the core paradoxical predictions of Wigner's friend experiment while maintaining objective states, challenging the need for quantum interpretations of measurement and observer effects.

Contribution

The paper introduces a classical model that reproduces Wigner's friend paradoxical predictions with objective states, offering a new perspective on quantum measurement puzzles.

Findings

The toy model reproduces Wigner's friend paradox within a classical framework.

Objective states can explain measurement conflicts without quantum superpositions.

Extensions with multiple observers cannot be explained classically, highlighting quantum features.

Abstract

The original Wigner's friend paradox is a gedankenexperiment involving an observer described by an external agent. The paradox highlights the tension between unitary evolution and collapse in quantum theory, and is sometimes taken as requiring a reassessment of the notion of objective reality. In this note however we present a classical toy model in which (i) The contradicting predictions at the heart of the thought experiment are reproduced (ii) Every system is in a well-defined state at all times. The toy model shows how puzzles such as Wigner's friend's experience of being in a superposition, conflicts between different agents' descriptions of the experiment, the positioning of the Heisenberg's cut and the apparent lack of objectivity of measurement outcomes can be explained within a classical model where there exists an objective state of affairs about every physical system at all times. Within the model, the debate surrounding the original Wigner's friend thought experiment and its resolution have striking similarities with arguments concerning the nature of the second law of thermodynamics. The same conclusion however does not apply to more recent extensions of the gedankenexperiment featuring multiple encapsulated observers, and shows that such extensions are indeed necessary avoid simple classical explanations.