1 Primitive Ontology and the Structure of Fundamental Physical Theories

For a long time, it was believed that it was impossible to be realist about quantum mechanics. It took quite a while for the researchers in the foundations of physics, beginning with John Stuart Bell (1987), to convince others that such an alleged impossibility had no foundation. These days there are several quantum theories that can be interpreted in a realist fashion, among which Bohmian mechanics, the Ghirardi-Rimini-Weber (GRW) theory, and the many-worlds theory. The debate, though, is far from being over. In what respect should we be realist regarding these theories? At least two different proposals have been made: on one hand, some insist on a direct ontological interpretation of the wave function as representing physical bodies, on the other hand are those who claim that quantum mechanics is not really about the wave function. In this chapter I will present and discuss one proposal of the latter kind that focuses on the notion of primitive ontology. 1. Wave Function Ontology There is a realist take on quantum theories according to which quantum mechanics is a theory about the behavior of an object called the wave function.1 That is, the wave function mathematically represents a real, physical field that constitutes physical objects. For this reason, such a view has been called wave function ontology. One of the strongest arguments for this view is an argument by analogy. If in a physical theory there is a fundamental equation for the evolution of a given mathematical object, generally we feel justified to take this entity to represent physical objects. Consider classical mechanics: the fundamental equation of this theory is Newton's equation that describes the tempora