arXiv subjects

Ulrich J. Mohrhoff

Publications and source records attributed to Ulrich J. Mohrhoff.

3 recordsLinked to original sources

arXiv2022

Bohr, objectivity, and "our experience": À propos Mermin's note on the quantum measurement problem

In a recent note David Mermin attributed the idea that wave function collapse is a physical process to a misunderstanding of probability and the role it plays in quantum mechanics. There are, however, further misconceptions at play, some of which are shared by Mermin himself and more generally by QBists. The main objective of the present comment on his note is to explain why I disagree with his reading of a well-known passage by Niels Bohr, in particular the ambiguity of the first-person plural he perceives in Bohr's reference to "our description of nature" and "our experience."

quant-ph↗

arXiv2020

Niels Bohr, objectivity, and the irreversibility of measurements

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.

physics.hist-ph↗

arXiv2019

Bohr, QBism, and Beyond

QBism may be the most significant contribution to the search for meaning in quantum mechanics since Bohr, even as Bohr's philosophy remains the most significant revision of Kant's theory of science. There are two ironies here. Bohr failed to realize the full extent of the affinity of his way of thinking with Kant's, and QBists fail to realize the full extent of their agreement with Bohr. While Bohr's discovery of contextuality updates Kant's transcendental philosophy in a way that leaves the central elements of the latter intact, Kant's insight into the roles that our cognitive faculties play in constructing physical theories can considerably alleviate the difficulties that Bohr's writings present to his readers. And while throwing a QBist searchlight on Bohr's writings can further alleviate these difficulties (as well as reveal the presence in them of the salient elements of QBist thought), Bohr's writings can in turn provide answers to important questions that QBism leaves unanswered (and also allay some of QBism's excesses). In the final sections I confront the two most impenetrable mysteries yet unearthed: making sense of quantum mechanics, and the dual mystery of making sense of (i) the existence of consciousness in a seemingly material world and (ii) the existence in consciousness of a seemingly material world. Here the relevant arguments are framed in the context of the philosophy of the Upanishads, according to which we (as Schrödinger put it) "are all really only various aspects of the One." There is no world that exists out of relation to consciousness, but there are different poises of consciousness. In particular, there is a poise of consciousness peculiar to the human species at this point in time, and there are poises of consciousness that are yet to evolve (and that may be essential to averting the calamities towards which humanity appears to be heading).

quant-ph↗