Importance of Reversibility in the Quantum Formalism

Abstract

In this letter I stress the role of causal reversibility (time-symmetry), together with causality and locality, in the justification of the quantum formalism. Firstly, in the algebraic quantum formalism, I show that the assumption of reversibility implies that the observables of a quantum theory form an abstract real C*-algebra, and can be represented as an algebra of operators on a real Hilbert space. Secondly, in the quantum logic formalism, I emphasize which axioms for the lattice of propositions (existence of an orthocomplementation and the covering property) derive from reversibility. A new argument based on locality and Soler's theorem is used to derive the representation as projectors on a regular Hilbert space from the general quantum logic formalism. In both cases it is recalled that the restriction to complex algebras and Hilbert spaces comes from the constraints of locality and separability.

4 pages, LaTeX. Title modified and a few misprints corrected from version 2. Differences with version 1: Extensive rewriting, no changes in the results, review material much shortened, starting points more extensively discussed, more emphasis on the three original points of the paper. The reader interested in the underlying formalism may still look at the compatible version arXiv:1103.3454v1