On the Empirical Significance of Physical Symmetries

Just in the last six years, a new debate has emerged around the question of whether or not modern gauge symmetries can be empirically significant, either in a way analogous to boosts in Galileo's ship thought experiment or in some 'non-relational' manner (i.e., in a manner where there is not an external system that allows us to distinguish between the symmetry-related states of the original system). The first two chapters of the dissertation tackle this debate. In the first one, I defend the claim that there can indeed be gauge symmetries that are empirically significant in a way analogous to boosts, and in the second chapter, I show that gauge symmetries cannot be empirically significant in a non-relational way and connect this issue to recent developments in theoretical physics (i.e., 'edge modes'). In the second half of the dissertation, I clarify the conditions under which symmetry-related states can be taken to be representionally equivalent.