Wigner's Frame

TL;DR

The paper tackles the Extended Wigner's Friend puzzle by proposing that properties are meaningful with respect to external reference frames only if tied to a symmetry, while observed outcomes remain absolute within an observer’s frame. It introduces a framework distinguishing invariant, frame-independent facts from frame-relational properties, and uses variables such as $A_I$, $A_E$, and $A_R$ to show how Alice’s observation can be definite even when inter-frame relations are indefinite, preserving quantum predictions without resorting to retrocausality or nonlocality. A key contribution is a symmetry-based account that blocks an infinite regress of relativization and provides a coherent route to connect relational QM with decoherence and Healey-like pragmatism, while preserving a realist core about invariant subsystems. The approach is argued to be broadly applicable to measurement problems and to supply a principled criterion for what must be relativized, with the caveat that the emergence of reference frames themselves requires further theoretical grounding.

Abstract

This article suggests that thinking about the role of reference frames can provide new insight into Extended Wigner's Friend scenarios. This involves appealing to symmetries to make a principled distinction between properties of a system which are meaningful only relative to an external reference system and properties which are meaningful without further relativization. Thus we may propose that there are always well-defined facts about what observers have observed, but there are not necessarily well-defined facts about the relations between their reference frames, so there will not always exist a joint distribution over their outcomes which can meaningfully be compared to the predictions of quantum mechanics. In addition, this approach also offers a general argument against the idea that there should be a regress of relativization.