Importance of Reversibility in the Quantum Formalism

TL;DR

This paper explores how causal reversibility, along with causality and locality, underpins the mathematical structure of quantum theory, emphasizing the role of reversibility in deriving key formal aspects.

Contribution

It demonstrates that reversibility leads to the algebraic and logical structures of quantum formalism, providing new insights into the foundations of quantum theory.

Findings

Reversibility implies observables form a real C*-algebra.

Reversibility influences axioms of quantum logic.

Locality and separability restrict to complex Hilbert spaces.

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.