Niels Bohr, objectivity, and the irreversibility of measurements

TL;DR

This paper explores Niels Bohr's perspective on the objectivity and irreversibility of measurements, emphasizing the role of sensory experience and experimental context in quantum mechanics.

Contribution

It clarifies Bohr's nuanced view on objectivity, linking it to Kantian philosophy and highlighting the weaker grounding of objectivity in quantum mechanics compared to classical physics.

Findings

Bohr's objectivity relies on sensory experience and experimental context.

Bohr's view is weaker than Kant's or Newtonian objectivity.

Irreversibility in measurement is tied to sensory and amplification effects.

Abstract

The only acceptable reason why measurements are irreversible and outcomes definite is the intrinsic definiteness and irreversibility of human sensory experience. While QBists deserve credit for their spirited defense of this position, Niels Bohr urged it nearly a century ago, albeit in such elliptic ways that the core of his message has been lost or distorted beyond recognition. Then as now, the objectivity of empirical science was called into question. It was defended by Bohr along the lines of Kant's (then) revolutionary theory of science, according to which the possibility of empirical science hinges on the possibility of thinking of experiences as experiences of a system of interacting, re-identifiable objects. What Bohr added to Kant's theory was his insight that empirical knowledge was not necessarily limited to what is directly accessible to the senses, and that, therefore, it does not have to be solely a knowledge of objects of sensible intuition. It can also be a knowledge of phenomena that are not objects of sensible intuition but instead are constituted by experimental contexts, which are objects of sensible intuition. Bohr's grounding of objectivity (or the objectivity consistent with quantum mechanics), however, is weaker than Kant's (or the objectivity consistent with Newtonian physics). This conclusion is based on an examination of Bohr's intentions in appealing to irreversible amplification effects or the sufficient size and weight of the measurement apparatus.