Critics have pointed to conflicting currents in QBism's philosophical self-conception insofar as QBist professions of realism sit uneasily with its Ansatz of personal experience. Rather than dropping the former and turning to phenomenology or to William James’ “radical empiricism”, I suggest that – if QBism is to be considered an interpretation of quantum mechanics – reconciliation may be found by following Bohr in drawing out and applying the non-representational consequences of the quantum postulate. While similarities to a position Rorty termed “epistemological behaviorism” are apparent, QBism can avoid Rorty's anti-representational deconstruction of epistemology by adopting, as did Bohr, a moderate empirical realism about the quantum world.
Critics have pointed to conflicting currents in QBism's philosophical self-conception insofar as QBist professions of realism sit uneasily with its Ansatz of personal experience. Rather than dropping the former and turning to phenomenology or to William James’ “radical empiricism”, I suggest that – if QBism is to be considered an interpretation of quantum mechanics – reconciliation may be found by following Bohr in drawing out and applying the non-representational consequences of the quantum postulate. While similarities to a position Rorty termed “epistemological behaviorism” are apparent, QBism can avoid Rorty's anti-representational deconstruction of epistemology by adopting, as did Bohr, a moderate empirical realism about the quantum world.
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."
A discrepancy between the instrumentalist and realist inclinations of QBism, or between its experiential and interactional concepts of measurement, has been repeatedly noticed. Here, we show that this discrepancy can be resolved by adopting a phenomenological approach throughout. In other terms, the difficulty can be overcome by unambiguously choosing the first-person standpoint as a radical origin of knowledge, and by ascending from the situated lived experience of a knowing and acting subject, to the structure and use of the quantum formalism. To reconstruct some crucial features of the objectivity promised by science, and to accommodate the soundest aspect of the realist intuitions of QBist authors, a phenomenological reinterpretation of what is commonly called “the world” is proposed. This reinterpretation is based on Bruce Bégout's “Eco-Phenomenology”, that replaces the concept of a somehow extrinsic relation between subject and world, with the immersive experience of a subject partaking of the world.
A critique of phenomenological interpretation of quantum Bayesianism (QBism) is offered, in particular, the position of M. Bitbol and L. de La Tremblay, which removes remnants of scientific realism from QBism and adopts a radically phenomenological first person point of view. It is shown that phenomenological view of quantum mechanics cannot explain cognition of quantum reality and behavior of real quantum systems, because the ultimate reality for phenomenology is autonomous phenomena, which, in fact, do not exist. Our proposed contextual quantum realism (CQR) does not invert, as the mentioned authors do, but rejects, the traditional relation between experience and reality. By reinterpreting QBism, our CQR removes remnants of phenomenology from it, but in such a way as not to fall into the other extreme – metaphysical realism.
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.
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.
Abstract QBism is an agent-centered interpretation of quantum theory. It rejects the notion that quantum theory provides a God’s eye description of reality and claims instead that it imposes constraints on agents’ subjective degrees of belief. QBism’s emphasis on subjective belief has led critics to dismiss it as antirealism or instrumentalism, or even, idealism or solipsism. The aim of this paper is to consider the relation of QBism to scientific realism. I argue that while QBism is an unhappy fit with a standard way of thinking about scientific realism, an alternative conception I call “perspectival normative realism” may allow for a reconciliation.