Observer-resolved transition algebra in classical mechanics

Lyudvig Dmitrievich Faddeev, O. Yakubovskiĭ

Pöttinger, Jürgen

Nicolaas P. Landsman

A synthesis is attempted between the algebraic theory of superselection sectors (not necessarily of infinite systems), which is based on the representation theory of C* algebras (which we review), and recent ideas on the measurement problem, classical behavior in open quantum systems, and the peculiar nature of subsystems in quantum mechanics. The key point is a proper use of the notion of a state, in combination with an appropriate choice of algebras of observables for which the superposition “principle” may be invalid. In this way, a major part of the measurement problem becomes equivalent to the study of superselection sectors in models for a measurement situation, and can in principle be resolved unambiguously. Special emphasis is placed on the transition from pure to mixed states, and the (non)uniqueness of the decomposition of the latter into pure states.

J. Pöttinger

Local observables of an infinite system are described by a quasilocal C*-algebra A. Traditionally classical observables are introduced as parameters that can be assigned to certain states on the local observables. As fundamental theories should be essentially free of parameters this can hardly be regarded as satisfactory. In the present paper classical observables are introduced explicitly as operators by a transitive system of imprimitivity of a kinematical group in the center of the W*-algebra π(A)″ belonging to a representation π of A. The states of the system are represented by linear functionals on π(A)″, which are dispersion-free on the center of π(A)″. For classical observables related to a kinematical group a W*-description—with algebra π(A)″ and its associated linear functionals that are dispersion-free on the center and normal on the noncentral part of π(A)″—is equivalent to a C*-description—with algebra A and a distinguished family of linear functionals on A, determined uniquely by π. The implications of these results on the interpretation of quantum mechanics of infinite systems are discussed.

Partha Ghose, Manoj K. Samal

Holger Neumann