Invariance, intrinsicality and perspicuity

Abstract

It is now standard to interpret symmetry-related models of physical theories as representing the same state of affairs. Recently, a debate has sprung up around the question when this interpretational move is warranted. In particular, Moller-Nielsen (2017) has argued that one is only allowed to interpret symmetry-related models as physically equivalent when one has a characterisation of their common content. I disambiguate two versions of this claim. On the first, a perspicuous interpretation is required: an account of the models' common ontology. On the second, stricter, version of this claim, a perspicuous formalism is required in addition: one whose mathematical structures 'intrinsically' represent the physical world, in the sense of Field (1980). Using Dewar (2019)'s distinction between internal and external sophistication as a case study, I argue that the second requirement is decisive. This clarifies the conditions under which it is warranted to interpret symmetry-related models as physically equivalent.Acknowledgements: I would like to thank Marta Bielińska, Adam Caulton, Neil Dewar, Henrique Gomes, Oliver Pooley and James Read for their insightful comments and discussions. I would also like to thank an audience at the Philosophy of Physics Graduate Lunch Seminar in Oxford and a helpful anonymous reviewer.

The Nature of a Constant of Nature: The Case of G

“…10 The excision of redundant structure from the theory's kinematics is a virtue; this virtue is undone if the same redundancies recur in the dynamics. I will therefore develop an alternative interpretation of (1) on which no quantification over 10 For more explicit discussions, see Sider (2020), Dewar (2021) and Jacobs (2022).…”