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

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.