Methodological Realism and Quantum Mechanics

TL;DR

This paper explores two different notions of completeness in quantum mechanics, contrasting the Everettian and Bohrian interpretations, and discusses their philosophical implications from metaphysical and methodological realism perspectives.

Contribution

It clarifies the distinction between two senses of completeness in quantum theory and analyzes how different interpretations align with these notions.

Findings

Everettian approach aims for ontological completeness

Bohrian approach emphasizes conceptual completeness

Interpretations can be mutually supportive despite opposition

Abstract

I distinguish two senses in which one can take a given physical theory to be `complete'. On the first, a complete physical theory is one that, in principle, completely describes physical reality. On the second, a complete physical theory is one that provides all of the conceptual resources one needs to describe any (in general probabilistic) physical phenomenon to any level of detail one likes, in principle. I argue that while the (neo-)Everettian approach to interpreting quantum mechanics aims to show that it is complete in the first sense, the (neo-)Bohrian approach begins from an understanding of quantum mechanics as being complete in the second sense. I then discuss some of the essential differences between how classical and quantum theory describe phenomena, and the way in which the quantum description can be thought of as a ``natural generalisation'' (to use Bohr's phrase) of the classical description. Finally, I elaborate upon the two visions of physics from which one can motivate the first and the second sense of completeness, respectively: \emph{metaphysical realism}, on the one hand, and what I will call \emph{methodological realism}, on the other -- and discuss what one can say about the significance of the differences between quantum and classical description from each of these points of view. I suggest that there is a sense in which the views of (neo-)Everett and the views of (neo-)Bohr can be understood to be mutually supporting positions, from their respective perspectives, even though they are diametrically opposed.