NBA History of Science Seminar

Don Howard, Department of Philosophy, University of Notre Dame

Don Howard (Department of Philosophy,
University of Notre Dame), "Complementarity and Decoherence"

This talk explores the relationship between Niels Bohr’s complementarity interpretation of quantum mechanics and modern work on decoherence. It combines historical analysis with a systematic investigation of foundational issues. I will start by presenting my own articulation of the concept of complementarity and my attempt at reconstructing the concept in a more rigorous, technical form via the notion of “context-dependent mixtures,” which, I argue, very precisely captures the key insight in Bohr’s thinking and also explains, in a novel manner, Bohr’s views on the role of classical concepts in quantum physics. I will then argue that complementarity, so understood, is critical to understanding the precise sense in which, as it is said, the decoherence dynamics, which is really just Schrödinger dynamics, drives a system-instrument pair, entangled with environmental degrees of freedom, into a pure state that is “observationally indistinguishable” from a mixture over eigenstates.