O.S. Groeneveld
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Wigner’s Friend: Memory, Awareness and Observer-Dependent Realities
Memory and Awareness of Wigner’s Friend
In this paper we analyze the Extended Wigner’s Friend Scenario as presented by Baumann & Brukner. The conclusion—that awareness of any change in the Friend’s ‘internal record’ is impossible—is argued to follow from the no-signaling principle. However, we show that this conclusion relies on combining two contradictory assumptions: 1) the lab is perfectly isolated, and 2) Wigner is a super-observer with complete control over the lab. Accepting both implies that the Friend’s ‘record’ is quantum erased, making awareness impossible by definition. To model awareness properly, we introduce a notebook—a stable, unerasable record of the Friend’s measurement result. This notebook forces a rejection of at least one of the original assumptions, resulting in a fundamentally different physical context. We demonstrate how this change affects the wavefunctions and joint measurement probabilities, revealing that Baumann & Brukner’s reasoning effectively compares outcomes across incompatible contexts. Next, we investigate the physical nature of observers and measurements, proposing a more realistic model in which an observer’s state consists of many quantum subsystems. Perfect isolation or complete control becomes implausible, and naturally leads stabilization of the state of the observer. These stable systems constitute an objective reality accessible to other observers, while unstable, erasable systems remain subjective and observer-relative. Our analysis supports an observer-dependent stance on facts in quantum mechanics, where both subjective and objective realities can coexist. This aligns closely with Relational Quantum Mechanics and provides a consistent framework for interpreting Wigner’s Friend-type scenarios. ...
In this paper we analyze the Extended Wigner’s Friend Scenario as presented by Baumann & Brukner. The conclusion—that awareness of any change in the Friend’s ‘internal record’ is impossible—is argued to follow from the no-signaling principle. However, we show that this conclusion relies on combining two contradictory assumptions: 1) the lab is perfectly isolated, and 2) Wigner is a super-observer with complete control over the lab. Accepting both implies that the Friend’s ‘record’ is quantum erased, making awareness impossible by definition. To model awareness properly, we introduce a notebook—a stable, unerasable record of the Friend’s measurement result. This notebook forces a rejection of at least one of the original assumptions, resulting in a fundamentally different physical context. We demonstrate how this change affects the wavefunctions and joint measurement probabilities, revealing that Baumann & Brukner’s reasoning effectively compares outcomes across incompatible contexts. Next, we investigate the physical nature of observers and measurements, proposing a more realistic model in which an observer’s state consists of many quantum subsystems. Perfect isolation or complete control becomes implausible, and naturally leads stabilization of the state of the observer. These stable systems constitute an objective reality accessible to other observers, while unstable, erasable systems remain subjective and observer-relative. Our analysis supports an observer-dependent stance on facts in quantum mechanics, where both subjective and objective realities can coexist. This aligns closely with Relational Quantum Mechanics and provides a consistent framework for interpreting Wigner’s Friend-type scenarios.