Gordon Belot: The Wave Function for Primitive Ontologists

The speaker begins by addressing the common question about why philosophers spend time discussing quantum mechanics when quantum field theory might be more relevant. They liken the study of quantum mechanics to a 'warm-up exercise' that prepares for the complexities of quantum field theory. The speaker admits their lack of expertise in quantum field theory and introduces the concept that any adequate understanding of quantum mechanics should be able to interpret the experiments that form the basis of the theory. They also touch on the 'measurement problem' and the 'macro object problem,' setting the stage for a discussion on different approaches to these issues in quantum mechanics.

This paragraph delves into the macro object problem within quantum mechanics, which concerns explaining how macroscopic objects like a walrus or a tester can be accounted for in quantum theory. The speaker discusses two main approaches to this problem: one by David Walsh that emphasizes the wave function as the fundamental ontology in quantum mechanics, and another that suggests a more direct correlation between quantum and classical worlds. The latter approach, known as the primitive ontology approach, associates the history of quantum particles with specific points in space-time, offering a more straightforward interpretation of quantum mechanics.

The speaker explores Bohmian mechanics, a theory that provides a deterministic interpretation of quantum mechanics by introducing a 'pilot wave' that guides particle trajectories. They discuss the role of the wave function in this theory, which includes governing the motion of particles and determining probabilities. The paragraph also addresses different interpretations of the wave function itself, including viewing it as a property, a thing, or a law. Each interpretation comes with its own set of philosophical and technical challenges, which are briefly examined.

In this paragraph, the speaker examines the idea of the wave function as a physical entity or a property in more detail. They consider the possibility of the wave function being a field on configuration space, as suggested by David Albert, and compare it to the notion of a classical field. The speaker also discusses the challenges of considering the wave function as a dispositional property, given its role in determining both the motion and probabilities in quantum systems. The complexities of these interpretations are highlighted, especially in the context of the GRW (Ghirardi-Rimini-Weber) model of quantum mechanics.

The speaker presents the idea of viewing the wave function as a law within the framework of quantum mechanics. They discuss the implications of this perspective for the understanding of the quantum-to-classical transition and the role of the wave function in determining the motion of particles. The paragraph also touches on the potential for the wave function to be time-independent and simple in a quantum theory of the entire universe, which could resolve some of the philosophical issues with this interpretation.

This paragraph provides an overview of the GRW (Ghirardi-Rimini-Weber) model, which introduces a stochastic process of wave function collapse to explain the emergence of definite outcomes in quantum measurements. The speaker discusses the algorithmic nature of the GRW model, which involves the wave function at a given time and the probability distribution over future 'flashes' or collapse events. The paragraph also explores the challenges of specifying the wave function in the context of the GRW model, including different strategies for representing wave function facts in addition to the flashes.

The speaker continues the discussion on the representation of wave function facts in quantum theory, considering different strategies for dealing with the wave function in the context of the GRW model. They explore the implications of these strategies for the understanding of locality in quantum mechanics, highlighting the complexities and potential non-locality that can arise from different representations of the wave function.

In this paragraph, the speaker examines the issue of locality in the context of a relativistic quantum theory, specifically discussing a model developed by Tommaso Bolognesi. They explore the implications of this model for the understanding of particle flashes and the representation of the wave function in a relativistic spacetime. The speaker also discusses the potential for different strategies in representing the wave function to affect the perceived locality of the theory.

The speaker concludes the discussion by reflecting on the philosophical implications of different interpretations of quantum mechanics. They consider the idea of 'primitive ontology' and the role of the wave function in determining the probabilities and dynamics of quantum systems. The paragraph also touches on the challenges of understanding the wave function as a physical entity, property, or law, and the potential for these interpretations to be influenced by the finite or infinite nature of the past in quantum theory.