A Matter of Degree: Putting Unitary Equivalence to Work

Ruetsche, Laura (2002) A Matter of Degree: Putting Unitary Equivalence to Work.

Abstract

A characteristic feature of quantum field theory is the availability of unitarily inequivalent representations of its canonical commutation relations. Under the prima facie reasonable assumption that unitary equivalence is a necessary condition for physical equivalence, this availability implies that there are many physically inequivalent quantizations of any classical field theory. To explore this dramatic non-uniqueness, and its implications for our understanding of how physical theories delimit physical possibility, I examine some of the uses to which unitarily inequivalent representations are put in another setting in which they arise: the thermodynamic limit of quantum statistical mechanics.