Version: v1, Published online: 1998

Retrieved September 21, 2019, from https://www.rep.routledge.com/articles/thematic/quantum-logic/v-1

## Article Summary

The topic of quantum logic was introduced by Birkhoff and von Neumann (1936), who described the formal properties of a certain algebraic system associated with quantum theory. To avoid begging questions, it is convenient to use the term ‘logic’ broadly enough to cover any algebraic system with formal characteristics similar to the standard sentential calculus. In that sense it is uncontroversial that there is a logic of experimental questions (for example, ‘Is the particle in region R?’ or ‘Do the particles have opposite spins?’) associated with any physical system. Having introduced this logic for quantum theory, we may ask how it differs from the standard sentential calculus, the logic for the experimental questions in classical mechanics. The most notable difference is that the distributive laws fail, being replaced by a weaker law known as orthomodularity.

All this can be discussed without deciding whether quantum logic is a genuine logic, in the sense of a system of deduction. Putnam argued that quantum logic was indeed a genuine logic, because taking it as such solved various problems, notably that of reconciling the wave-like character of a beam of, say, electrons, as it passes through two slits, with the thesis that the electrons in the beam go through one or other of the two slits. If Putnam’s argument succeeds this would be a remarkable case of the empirical defeat of logical intuitions. Subsequent discussion, however, seems to have undermined his claim.

Forrest, Peter. Quantum logic, 1998, doi:10.4324/9780415249126-Y049-1. Routledge Encyclopedia of Philosophy, Taylor and Francis, https://www.rep.routledge.com/articles/thematic/quantum-logic/v-1.

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