Equivalence and Duality in Electromagnetism

Abstract

In this article I bring the recent philosophical literature on theoretical equivalence to bear on dualities in physics. Focusing on electromagnetic duality, which is a simple example of S-duality in string theory, I show that the duality fits naturally into at least one framework for assessing equivalence—that of categorical equivalence—but that it fails to meet a necessary condition for equivalence on that account. The reason is that the duality does not preserve “empirical content” in the required sense; instead, it takes models to models with “dual” empirical content. I conclude by discussing how one might react to this.