This project examines the role of Niels Bohr’s notion of classical concepts in the use and interpretation of quantum theory, and explores its operational consequences. Prior work has shown that Bohr’s “classical concepts” are conceptually distinct from “classical mechanics”: whereas classical mechanics concerns dynamical laws, classical concepts concern the epistemic and linguistic preconditions required to describe experiments and communicate their results (see, for example, Faye’s reconstruction of Bohr).

In the first part of the project, I investigate how these epistemic and linguistic preconditions might be formalized. In particular, they involve (i) the capacity to describe experimental outcomes as definite occurrences in ordinary language, and (ii) the capacity to communicate such occurrences intersubjectively.

In the second part, I explore how this formalization can be applied to concrete physical scenarios, and what logical and conceptual consequences follow for the quantum–classical transition and for interpretations of quantum theory.

In this project, I am examining the atomistic assumptions that underlie much of the physics of complex systems—assumptions that often support weak-emergence explanations—and exploring the possible role of strong emergence. Since Descartes, the dominant explanatory mode in physics has been reductionist: a system’s behavior is taken to be nothing more than the aggregate behavior of its constituent parts, which are presumed to exist independently and to be distinctly identifiable. In classical physics, this picture works well: a heap of sand can be treated as the sum of its grains, each with independent and well-defined existence, and classical statistical mechanics fits comfortably within this framework. This framework, when applied to quantum many-body theory, adopts a line of reasoning that assumes the universality of quantum theory: macroscopic objects are composed of particles; particles obey quantum theory; therefore, macroscopic objects obey quantum theory. This conclusion, however, is not a logical necessity but rather the manifestation of a metaphysical assumption. It is this underlying metaphysical assumption that is revisited in this project. Revisions to this assumption, motivated by closer alignment with experience, do not affect whether quantum theory is universal but instead affect the sense in which it is universal.

Quantum mechanics complicates this atomistic view. An operationally rigorous part–whole relation in quantum systems must account for the probing mechanisms through which “parts” are defined and accessed. This point has been demonstrated in the extensive literature on entanglement in identical particles—for example, in Paolo Zanardi et al.’s “Quantum Tensor Product Structures Are Observable-Induced” (Physical Review Letters 92, no. 6, 2004).

This project investigates quantum mereology—the relation between parts and wholes in quantum theory—using an operational approach that minimizes historically inherited metaphysical assumptions whose applicability may be limited.