It is suggested that the B in QBism rightfully stands for Bohr. The paper begins by explaining why Bohr seems obscure to most physicists. Having identified the contextuality of physical quantities as Bohr's essential contribution to Kant's theory of science, it outlines the latter, its proper contextuality (human experience), and its decontextualization. In order to preserve the decontextualization achieved by Kant's theory, Bohr seized on quantum phenomena as the principal referents of atomic physics, all the while keeping the universal context of human experience at the center of his philosophy. QBism, through its emphasis on the individual experiencing subject, brings home the intersubjective constitution of objectivity more forcefully than Bohr ever did. If measurements are irreversible and outcomes definite, it is because the experiences of each subject are irreversible and definite. Bohr's insights, on the other hand, are exceedingly useful in clarifying the QBist position, attenuating its excesses, and enhancing its internal consistency.
It is suggested that the B in QBism rightfully stands for Bohr. The paper begins by explaining why Bohr seems obscure to most physicists. Having identified the contextuality of physical quantities as Bohr's essential contribution to Kant's theory of science, it outlines the latter, its proper contextuality (human experience), and its decontextualization. In order to preserve the decontextualization achieved by Kant's theory, Bohr seized on quantum phenomena as the principal referents of atomic physics, all the while keeping the universal context of human experience at the center of his philosophy. QBism, through its emphasis on the individual experiencing subject, brings home the intersubjective constitution of objectivity more forcefully than Bohr ever did. If measurements are irreversible and outcomes definite, it is because the experiences of each subject are irreversible and definite. Bohr's insights, on the other hand, are exceedingly useful in clarifying the QBist position, attenuating its excesses, and enhancing its internal consistency.
It is suggested that the "B" in QBism rightfully stands for Bohr. The paper begins by explaining why Bohr seems obscure to most physicists. Having identified the contextuality of physical quantities as Bohr's essential contribution to Kant's theory of science, it outlines the latter, its proper contextuality (human experience), and its decontextualization. In order to preserve the decontextualization achieved by Kant's theory, Bohr seized on quantum phenomena as the principal referents of atomic physics, all the while keeping the universal context of human experience at the center of his philosophy. QBism, through its emphasis on the individual experiencing subject, brings home the intersubjective constitution of objectivity more forcefully than Bohr ever did. If measurements are irreversible and outcomes definite, it is because the experiences of each subject are irreversible and definite. Bohr's insights, on the other hand, are exceedingly useful in clarifying the QBist position, attenuating its excesses, and enhancing its internal consistency.
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).
QBism is a novel interpretation of quantum mechanics. With its radical emphasis on the subject, QBism provides a welcome corrective to popular misrepresentations of the epistemological reflections of Niels Bohr, while Bohr, rightly understood, can take the edge off QBism's radical subjectivism. Together, they form a winning combination, the key to which is Schrödinger's concept of objectivation, which has its roots in Kant's theory of science. Objectivation contrasts with objectification, the demonstrably futile attempt to make measurements yield outcomes in interpretations that reify a calculational device. Apart from providing an in-depth discussion of QBism, Kant, and Bohr, the paper addresses the issue of nonlocality, the scenario of Wigner's friend, Bell's shifty split, and the problem of the now. It also outlines an ontological interpretation that incorporates the insights of QBism and Bohr.
Without Niels Bohr, QBism would be nothing. But QBism is not Bohr. This paper attempts to show that, despite a popular misconception, QBism is no minor tweak to Bohr's interpretation of quantum mechanics. It is something quite distinct. Along the way, we lay out three tenets of QBism in some detail: 1) The Born Rule---the foundation of what quantum theory means for QBism---is a normative statement. It is about the decision-making behavior any individual agent should strive for; it is not a descriptive "law of nature" in the usual sense. 2) All probabilities, including all quantum probabilities, are so subjective they never tell nature what to do. This includes probability-1 assignments. Quantum states thus have no "ontic hold" on the world. 3) Quantum measurement outcomes just are personal experiences for the agent gambling upon them. Particularly, quantum measurement outcomes are not, to paraphrase Bohr, instances of "irreversible amplification in devices whose design is communicable in common language suitably refined by the terminology of classical physics." Finally, an explicit comparison is given between QBism and Bohr with regard to three subjects: a) The issue of the "detached observer" as it arose in a debate between Pauli and Bohr, b) Bohr's reply to Einstein, Podolsky, and Rosen, and c) Bohr's mature notion of "quantum phenomena." At the end, we discuss how Bohr's notion of phenomena may have something to offer the philosophy of William James: A physics from which to further develop his vision of the world---call it an ontology if you will---in which "new being comes in local spots and patches."
This is the first volume that focuses specifically on phenomenological approaches to quantum mechanics. It is also the first volume focusing on the philosophical implications of QBism. This coincidence is not accidental. Phenomenology's rich potential for our understanding of quantum mechanics has long been overlooked by analytic philosophers and phenomenologists alike. The experience-first approach of phenomenology, its descriptive methodology, and Husserl's critique of mathematization do not sit well with “mainstream” analytic philosophy of physics. But as this volume will demonstrate, it sits nicely with the basic tenets of QBism. Conversely, QBism constitutes the most consistent and best-developed interpretation of quantum mechanics that fully embraces the Bohrian idea that a proper understanding of science must be based on the concept of experience. However, since its inception in the early 2000s, QBism has struggled to connect with the philosophical community. Not only are the underlying intuitions shaping and dominating contemporary philosophy of quantum mechanics—namely, that a scientific theory must be purged of all subjective and operational notions such as “experience” or “measurement” and that, consequently, a successful approach to quantum mechanics must be formulated as a “quantum theory without observers”—at odds with QBism. It seems that sometimes the incommensurability already starts at the level of the basic conceptual framework which, in the case of mainstream analytic philosophy, is not very well suited to express some of QBism's main tenets. Considering this situation, the main hypothesis of this volume is that phenomenology and QBism are natural bedfellows, and that both can profit from mutual exchange. In order to make this exchange as profitable as possible, the aim of this introductory chapter is to identify, clarify, and motivate some of the cornerstones of phenomenological approaches to quantum mechanics, to shed light on the main ideas and virtues of QBism, and to discuss points of contact and points of possible conflict between these two projects.
After a summary of Bohr's views and their relation to Kant's theory of science, two fruitless lines of attack on the measurement problem are discussed: the way of the psi-ontologist and the way of the QBist. In the remainder of the paper the following results are obtained. (i) Because the testable correlations between outcomes of measurements of macroscopic positions are consistent with both the classical and the quantum laws, there is no conflict between the superposition principle and the existence of measurement outcomes. (ii) Intrinsically, each fundamental particle is numerically identical with every other fundamental particle. What presents itself here and now with these properties and what presents itself there and then with those properties is one and the same entity, herein called "Being." (iii) The distinction between a classical domain and a quantum domain is essentially a distinction between the manifested world and its manifestation. By entering into reflexive spatial relations, Being gives rise to (a) what looks like a multiplicity of relata if the reflexive quality of the relations is ignored, and (b) what looks like a substantial expanse if the spatial quality of the relations is reified. (iv) The reason why quantum mechanics is a calculus of correlations between measurement outcomes is that it concerns the progressive realization of distinguishable objects and distinguishable regions of space. (v) The key to the relation between quantum mechanics and experience is that Being does not simply manifest the world, Being manifests the world to itself. It is at once the single substance by which the world exists and the ultimate self or subject for which it exists. The question how we are related to this ultimate self or subject is discussed.