The Argument from Entanglement

In quantum mechanics, entangled states are not exotic or rare. Rather, entanglement is the norm and so the metaphysical consequences of entanglement are a central issue for anyone wishing to provide an ontological interpretation of the various formulations of quantum mechanics. This chapter presents the argument for wave function realism from quantum entanglement, which says that wave function realism is necessary if one wants an ontological interpretation that does not conflate distinct quantum states. It explains quantum entanglement and how postulating a wave function in higher dimensions can help to metaphysically ground the phenomenon. The chapter ultimately concludes that the argument from quantum entanglement fails as there are several rival positions that can also explain quantum entanglement and recover the distinctions between different entangled states. These include the primitive ontology approach, various other holisms, ontic structural realism, spacetime state realism, and the multi-field approach.

Must an Ontology for Quantum Theories Contain Local Beables?

This chapter considers and responds to the objection that a wave function in a high-dimensional space cannot ultimately constitute the low-dimensional macroscopic objects of experience. It discusses two forms this objection takes: one based on the putative fact that our evidence for quantum theories consists of low-dimensional objects, and another based on the putative fact that quantum theories are about low-dimensional objects, that they have primitive ontologies of local beables. Even admitting that there may be something straightforward and comprehensible about the fundamental ontologies for quantum theories proposed by the wave function realist, the philosophers who raise these objections see a problem with these ontologies in that they cannot serve as the constitutive foundation for the world as we experience it. And this undermines the promise of wave function realism to serve as a framework for the interpretation of quantum theories.

The Causal Role of Macroscopic Objects

This chapter considers and critiques some strategies for solving the macro-object problem for wave function realism. This is the problem of how a wave function understood as a field on a high-dimensional space may come to make up or constitute the low-dimensional, macroscopic objects of our experience. It is first noted that simply invoking correspondences between particle configurations and states of the wave function will not suffice to solve the macro-object problem, following issues noted previously by Maudlin and Monton. More sophisticated strategies are considered that appeal to functionalism. It is argued that these functionalist strategies for recovering low-dimensional macroscopic objects from the wave function also do not succeed.

Finding the Macroworld

This chapter proposes a solution to the macro-object problem for wave function realism. This is the problem of how a wave function in a high-dimensional space may come to constitute the low-dimensional, macroscopic objects of our experience. The solution takes place in several stages. First, it is argued that how the wave function’s being invariant under certain transformations may give us reason to regard three-dimensional configurations corresponding symmetries with ontological seriousness. Second it is shown how the wave function may decompose into low-dimensional microscopic parts. Interestingly, this reveals mereological relationships in which parts and wholes inhabit distinct spatial frameworks. Third, it is shown how these parts may come to compose macroscopic objects.

A Preliminary Case for Wave Function Realism

This chapter explains the use of wave functions in quantum mechanics in order to develop a preliminary argument for wave function realism, one that is commonly found in the physics and philosophy of physics literature. It distinguishes ontological questions about the status of the wave function from the more discussed measurement problem for quantum mechanics, and explains how wave function realism is an approach to ontology that is compatible with several rival solutions to the measurement problem. The chapter then presents an initial, but not ultimately decisive, argument for wave function realism based on the ubiquity of wave function representations in quantum physics.

The Virtues of Separability and Locality

This chapter presents the argument for wave function realism that it is the only realist interpretation of quantum theories that can maintain a fundamentally separable and local metaphysics. It is commonly seen as a consequence of entanglement and Bell’s Theorem that quantum mechanics entails quantum nonseparability and nonlocality. Yet although all rival realist ontological interpretations of quantum mechanics involve either a nonseparable or a nonlocal fundamental metaphysics, the metaphysics of wave function realism is fundamentally both separable and local, although the view also makes room for nonfundamental nonseparability and nonlocality. The chapter considers several arguments that could explain why one should prefer interpretations of quantum theories that are separable and local, and concludes with a defense of intuitions in quantum interpretation.

Wave Function Realism in a Relativistic Setting

This chapter considers and responds to criticism that wave function realism is only plausible as an approach to the interpretation of nonrelativistic quantum mechanics and not relativistic quantum theories and quantum field theories. This critique gains traction as wave function realism has until now been formulated and defended solely within the context of idealized, nonrelativistic quantum mechanics. The chapter considers five such arguments and responds to each. An important lesson is that wave function realists should only adopt the wave-function-in-configuration-space picture as part of an interpretation of an idealized nonrelativistic quantum mechanics. More generally, the space the wave function inhabits will vary as the quantum theory the wave function realist is developing an interpretation of varies. The chapter develops a sketch of what wave function realism looks like in one relativistic context. It then discusses the issue of the interpretation of quantum theories in the limit of physical theorizing.