Niels Bohr on the wave function and the classical/quantum divide

TL;DR

This paper re-examines Niels Bohr's interpretation of quantum mechanics, emphasizing the mutual dependence of classical and quantum concepts and clarifying his view on the wave function and measurement problem.

Contribution

It offers a new interpretation of Bohr's ideas, distinguishing his symbolic wave function from epistemic and ontological views, and relates his perspective to modern quantum gravity and cosmology.

Findings

Bohr's classical concepts are essential for understanding quantum phenomena.

His wave function is best seen as symbolic, not purely epistemic or ontological.

Bohr's interpretation differs from standard Copenhagen and other reconstructions.

Abstract

It is well known that Niels Bohr insisted on the necessity of classical concepts in the account of quantum phenomena. But there is little consensus concerning his reasons, and what he exactly meant by this. In this paper, I re-examine Bohr's interpretation of quantum mechanics, and argue that the necessity of the classical can be seen as part of his response to the measurement problem. More generally, I attempt to clarify Bohr's view on the classical/quantum divide, arguing that the relation between the two theories is that of mutual dependence. An important element in this clarification consists in distinguishing Bohr's idea of the wave function as symbolic from both a purely epistemic and an ontological interpretation. Together with new evidence concerning Bohr's conception of the wave function collapse, this sets his interpretation apart from both standard versions of the Copenhagen interpretation, and from some of the reconstructions of his view found in the literature. I conclude with a few remarks on how Bohr's ideas make much sense also when modern developments in quantum gravity and early universe cosmology are taken into account.