Perspectival Quantum Realism

TL;DR

The paper proposes a perspectival quantum realism that maintains an objective physical world by allowing properties to be perspective-dependent, addressing interpretational issues in quantum mechanics without abandoning realism.

Contribution

It introduces a perspectival approach to quantum realism, combining relational ideas with objective properties, and applies it to classic quantum scenarios like Wigner's friend and EPR.

Findings

Perspectivalism offers a way to reconcile objectivity with agent-dependent perspectives.

The approach can be formulated as local or nonlocal.

It connects quantum perspectivalism to fragmentalism in philosophy.

Abstract

The theories of pre-quantum physics are standardly seen as representing physical systems and their properties. Quantum mechanics in its standard form is a more problematic case: here, interpretational problems have led to doubts about the tenability of realist views. Thus, QBists and Quantum Pragmatists maintain that quantum mechanics should not be thought of as representing physical systems, but rather as an agent-centered tool for updating beliefs about such systems. It is part and parcel of such views that different agents may have different beliefs and may assign different quantum states. What results is a collection of agent-centered perspectives rather than a unique representation of the physical world. In this paper we argue that the problems identified by QBism and Quantum Pragmatism do not necessitate abandoning the ideal of representing the physical world. We can avail ourselves of the same puzzle-solving strategies as employed by QBists and pragmatists by adopting a \emph{perspectival quantum realism}. According to this perspectivalism (close to the relational interpretation of quantum mechanics) objects may possess different, but equally objective properties with respect to different physically defined perspectives. We discuss two options for such a perspectivalism, a local and a nonlocal one, and apply them to Wigner's friend and EPR scenarios. Finally, we connect quantum perspectivalism to the recently proposed philosophical position of \emph{fragmentalism}.