The quantum-to-classical transition: Bohr's doctrine of classical concepts, emergent classicality, and decoherence

TL;DR

This paper explores how Bohr's doctrine of classical concepts relates to modern decoherence theory, showing that decoherence provides a physical basis for Bohr's quantum-classical divide and clarifies historical disagreements.

Contribution

It offers a nuanced analysis linking Bohr's classical concepts with decoherence, including a reinterpretation of historical debates and four formulations of classical concepts.

Findings

Decoherence justifies Bohr's quantum-classical divide

Historical disagreements between Bohr and Heisenberg are clarified

Four formulations of classical concepts are distinguished

Abstract

It is now widely accepted that environmental entanglement and the resulting decoherence processes play a crucial role in the quantum-to-classical transition and the emergence of "classicality" from quantum mechanics. To this extent, decoherence is often understood as signifying a break with the Copenhagen interpretation, and in particular with Bohr's view of the indispensability of classical concepts. This paper analyzes the relationship between Bohr's understanding of the quantum-classical divide and his doctrine of classical concepts and the decoherence-based program of emergent classicality. By drawing on Howard's reconstruction of Bohr's doctrine of classical concepts, and by paying careful attention to a hitherto overlooked disagreement between Heisenberg and Bohr in the 1930s about the placement of the quantum-classical "cut," we show that Bohr's view of the quantum-classical divide can be physically justified by appealing to decoherence. We also discuss early anticipations of the role of the environment in the quantum-classical problem in Heisenberg's writings. Finally, we distinguish four different formulations of the doctrine of classical concepts in an effort to present a more nuanced assessment of the relationship between Bohr's views and decoherence that challenges oversimplified statements frequently found in the literature.