In a recent no-go theorem [Bong et al., Nature Physics (2020)], we proved that the predictions of unitary quantum mechanics for an extended Wigner’s friend scenario are incompatible with any theory satisfying three metaphysical assumptions, the conjunction of which we call “Local Friendliness”: Absoluteness of Observed Events, Locality and No-Superdeterminism. In this paper (based on an invited talk for the QBism jubilee at the 2019 Växjö conference) I discuss the implications of this theorem for QBism, as seen from the point of view of experimental metaphysics. I argue that the key distinction between QBism and realist interpretations of quantum mechanics is best understood in terms of their adherence to different theories of truth: the pragmatist versus the correspondence theories. I argue that a productive pathway to resolve the measurement problem within a pragmatist view involves taking seriously the perspective of quantum betting agents, even those in what I call a “Wigner bubble”. The notion of reality afforded by QBism, I propose, will correspond to the invariant elements of any theory that has pragmatic value to all rational agents—that is, the elements that are invariant upon changes of agent perspectives. The classical notion of ‘event’ is not among those invariants, even when those events are observed by some agent. Neither are quantum states. Nevertheless, I argue that far from solipsism, a personalist view of quantum states is an expression of its precise opposite: Copernicanism.

在最近的不通过定理中[Bong等人，自然物理学（2020）]，我们证明了扩展的维格纳朋友场景的unit量子力学的预测与满足三个形而上学假设的任何理论都不相容，我们将它们结合在一起称为“当地友好”：观察事件的绝对性，局部性和无超确定性。在本文中（基于2019年Växjö会议上QBism周年庆典的邀请演讲），我将从实验形而上学的角度讨论了该定理对QBism的影响。我认为，QBism和量子力学的现实主义解释之间的关键区别最好是根据它们坚持不同的真理理论而理解的：实用主义与对应论。我认为，实用主义的观点来解决测量问题的一条有效途径涉及认真对待量子投注代理的观点，即使是那些我称之为“维格纳泡沫”的代理。我认为，QBism提供的现实概念将与任何对所有理性主体具有务实价值的理论的不变要素相对应，也就是说，主体视角变化时不变的要素。即使事件是由某些主体观察到的，经典的“事件”概念也不在这些不变式之中。量子态也不是。不过，我认为，量子论的个人主义观点远非唯唯诺论，而是其恰恰相反的一种表达：哥白尼主义。