Bohrification

TL;DR

This paper develops a new mathematical framework for quantum logic and phase space by combining algebraic quantum theory with topos theory, leading to an intuitionistic, distributive quantum logic that generalizes classical concepts.

Contribution

It introduces the concept of Bohrification, constructing a topos and an internal commutative C*-algebra to model quantum systems with a new intuitionistic quantum logic.

Findings

The Bohrified phase space S(A) is a locale with a Heyting algebra structure.

The quantum logic S(A) is distributive and intuitionistic, unlike traditional quantum logic.

For certain algebras, S(A) can be compared with the orthomodular lattice of projections.

Abstract

New foundations for quantum logic and quantum spaces are constructed by merging algebraic quantum theory and topos theory. Interpreting Bohr's "doctrine of classical concepts" mathematically, given a quantum theory described by a noncommutative C*-algebra A, we construct a topos T(A), which contains the "Bohrification" B of A as an internal commutative C*-algebra. Then B has a spectrum, a locale internal to T(A), the external description S(A) of which we interpret as the "Bohrified" phase space of the physical system. As in classical physics, the open subsets of S(A) correspond to (atomic) propositions, so that the "Bohrified" quantum logic of A is given by the Heyting algebra structure of S(A). The key difference between this logic and its classical counterpart is that the former does not satisfy the law of the excluded middle, and hence is intuitionistic. When A contains sufficiently many projections (e.g. when A is a von Neumann algebra, or, more generally, a Rickart C*-algebra), the intuitionistic quantum logic S(A) of A may also be compared with the traditional quantum logic, i.e. the orthomodular lattice of projections in A. This time, the main difference is that the former is distributive (even when A is noncommutative), while the latter is not. This chapter is a streamlined synthesis of 0709.4364, 0902.3201, 0905.2275.