How Real are Quantum States in $\psi$-ontic Models?

Abstract

There is a longstanding debate on the metaphysical relation between quantum states and the systems they describe. A series of relatively recent ψ-ontology theorems have been taken to show that, provided one accepts certain assumptions, "quantum states are real". In this paper I investigate the question of what that claim might be taken to mean in light of these theorems. It is argued that, even if one accepts the framework and assumptions employed by such theorems, such a conclusion is not warranted. Specifically, I argue that when a so-called ontic state is taken to describe the properties of a system, the relation between this state and some quantum state as established by ψ-ontology theorems, is not of the kind that would warrant counting the quantum state among these properties in any way.

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