The Contextual Modal Logic of a Wigner’s Friend Generalization

Abstract Quantum mechanics has been subject to logical scrutiny since its inception. The behavior of quantum systems, which are fundamentally dissimilar from classical systems, often appears to point to a logical inconsistency in quantum mechanics, allegedly leading to contradictions in the prediction of experimental measurements–though such contradictions have never materialized. A recent example of this type of inquiry into the logical well-posedness of quantum mechanics is the Frauchiger–Renner Gedankenexperiment, which purports to demonstrate that quantum mechanics is logically inconsistent under trivial assumptions. In this article, we show that by considering the property of contextuality in quantum systems–as predicted by the Kochen–Specker theorem–the supposed contradiction proposed by Frauchiger and Renner becomes logically inaccessible.