Abstract

This chapter argues that gauge symmetry is a purely formal feature of our theoretical representations with no empirical consequences. It distinguishes theoretical symmetries of a theory from empirical symmetries of situations to which a theory may be applied. A theoretical symmetry is purely formal if it implies no corresponding empirical symmetry. The chapter responds to several objections based on phenomena whose explanation apparently requires that gauge symmetry have empirical consequences. It argues that gauge symmetry is not observable and criticizes ‘the gauge argument’ from gauge symmetry to the existence of fundamental interactions. ‘Ghost’ fields are not real fields: despite its name, ‘spontaneous symmetry breaking’ does not involve any breaking of ‘local’ gauge symmetry; the theta-vacuum is not a superposition of distinct states inter-related by ‘large’ gauge transformations; anomalies in empirically successful theories do not involve breaking of any empirical gauge symmetry.