Same-diff? Conceptual similarities between gauge transformations and diffeomorphisms. Part II: Challenges to sophistication

TL;DR

This paper examines the metaphysical and mathematical aspects of gauge transformations and diffeomorphisms, proposing desiderata for their treatment under the 'sophistication' approach, and shows that general relativity and Yang-Mills theory meet these criteria.

Contribution

It extends the criteria for applying the 'sophistication' approach to symmetries and demonstrates their satisfaction in general relativity and Yang-Mills theory.

Findings

Both theories satisfy the first desideratum related to automorphisms.

Both theories satisfy the second desideratum involving axiomatizability.

The paper extends the criteria to more general theories.

Abstract

The following questions are germane to our understanding of gauge-(in)variant quantities and physical possibility: how are gauge transformations and spacetime diffeomorphisms understood as symmetries, in which ways are they similar, and in which are they different? To what extent are we justified in endorsing different attitudes -- nowadays called sophistication, haecceitism, and eliminativism -- towards each? This is the second of four papers taking up this question, and it is the one that most engages with the metaphysical debates surrounding our understanding of symmetry and equivalence. In this paper, I will provide two desiderata for the application of a treatment of symmetries known as `sophistication' and show that both general relativity and Yang-Mills theory satisfy these desiderata. The first desideratum for symmetries is mathematical, and was shown to hold for general relativity and Yang-Mills in the first paper: (i) that they correspond to the automorphisms of the structured base sets for the models of the two theories. Here I will extend the desideratum to more general theories. The second desideratum is mathematical-physical: (ii) that the general type of structure to which Desideratum (i) refers is axiomatizable and that this axiomatization can be phrased in terms of basic physical predicates of the theory. In the third paper in the series I will provide yet a third desideratum, to deal with an issue that goes beyond the standard debate about sophistication.