The Extended Wigner’s Friend, Many-and Single-Worlds and Reasoning from Observation

Journal article

The concept of an isolated system, and Frauchiger and Renner’s extended ‘Wigner’s friend’ scenario are discussed. It is argued that: (i) it is questionable whether the approximation of the isolated system is valid when measurement-like processes are involved; (ii) one may infer, from Frauchiger and Renner’s thought-experiment, and similar thought-experiments, that any interpretation of quantum theory involving subjective collapse fails; (iii) this does not distinguish single-world from many-world (relative-state) interpretations of quantum theory; (iv) reasoning from observations has to take into account the possible quantum-erasure of those observations if it is to be valid reasoning; (v) a single-world interpretation is valid if certain kinds of outcome are not quantum-erased in the future.

Authors: Steane, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Springer
• Journal: Foundations of Physics
• Volume: 55
• Issue: 2
• Article number: 20
• Publication date: 2025-03-07
• Acceptance date: 2025-02-12
• DOI: 10.1007/s10701-025-00831-8
• EISSN: 1572-9516
• ISSN: 0015-9018
• Language: English
• Keywords: Quantum measurement; Wigner’s friend; Isolated system; Interpretation of quantum mechanics