The original Wigner's-Friend scenarios

TL;DR

This paper revisits the original Wigner's-Friend paradox by tracing two historic formulations (Wigner's 1961 and Everett's 1956) and introducing decoherence as a third, environment-based resolution. It argues that each account—consciousness-induced collapse, unitary relative-state branching, and environment-induced decoherence—provides a consistent narrative when viewed from its own theoretical lens, without requiring a literal paradox to persist. By mapping the role of memory, apparatus, and environment, the work clarifies how definite outcomes emerge while preserving unitary dynamics. The analysis highlights the interconnectedness of observer-centric interpretations and decoherence, underscoring their collective relevance to contemporary quantum foundations and the interpretation of measurement results.

Abstract

We describe the Wigner's-Friend scenario according to Wigner, then a similar but earlier version according to Everett. Wigner and Everett provide different resolutions of essentially the same paradox. Decoherence theory provides a third resolution. Despite different interpretations (or their absence), these three stories fit together to form a consistent picture without a paradox.