Hans Halvorson (Princeton): Explanation via surplus structure

Our attempts to model physical systems seem to be cursed by the problem of surplus structure: our mathematical representations of such
systems contain structure which apparently has no analogue in the

system under study. When interpreting our theories; then; we invoke

some notion of “physical equivalence” of models in order to wash out

this surplus structure.

At least that’s how the story is typically told. I will argue; in

contrast; that surplus structure can itself be explanatory.

For concreteness; I will focus on the case of surplus structure in

quantum field theory. I will show that explanations in QFT trade on

the fact that there are multiple “representations” that are

nonetheless mathematically isomorphic.