QBism is currently one of the most widely discussed 'subjective' interpretations of quantum mechanics. Its key move is to say that quantum probabilities are personalist Bayesian probabilities and that the quantum state represents subjective degrees of belief. Even probability-one predictions are considered subjective assignments expressing the agent's highest possible degree of certainty about what they will experience next. For most philosophers and physicists this means that QBism is simply too subjective. Even those who agree with QBism that the wave function should not be reified and that we should look for alternatives to standard Psi-ontic interpretations often argue that QBism must be abandoned because it detaches science from objectivity. The problem is that from the QBist perspective it is hard to see how objectivity could enter science. In this paper, I introduce and motivate an interpretation of quantum mechanics that takes QBism as a starting point, is consistent with all its virtues, but allows objectivity to enter from the get-go. This is the view that quantum probabilities should be understood as objective degrees of epistemic justification.
QBism is currently one of the most widely discussed 'subjective' interpretations of quantum mechanics. Its key move is to say that quantum probabilities are personalist Bayesian probabilities and that the quantum state represents subjective degrees of belief. Even probability-one predictions are considered subjective assignments expressing the agent's highest possible degree of certainty about what they will experience next. For most philosophers and physicists this means that QBism is simply too subjective. Even those who agree with QBism that the wave function should not be reified and that we should look for alternatives to standard Psi-ontic interpretations often argue that QBism must be abandoned because it detaches science from objectivity. The problem is that from the QBist perspective it is hard to see how objectivity could enter science. In this paper, I introduce and motivate an interpretation of quantum mechanics that takes QBism as a starting point, is consistent with all its virtues, but allows objectivity to enter from the get-go. This is the view that quantum probabilities should be understood as objective degrees of epistemic justification.
This chapter expresses what a breath of fresh air it has been since a few phenomenological philosophers have started to engage with QBism. In service of the newfound discussion, the aim of this exposition is to lay out the structure of QBism as clearly as possible for that audience. In the process, we arrive at eight tenets for QBism: (1) A quantum state is an agent's personal judgment. (2) A quantum measurement is an agent's action upon its external world. (3) Quantum measurement outcomes are personal to the agent performing the action. (4) The quantum formalism is normative rather than descriptive. (5) Unitary evolution too expresses an agent's degrees of belief. (6) Even probability-one assignments are judgments without ontic content. (7) Subjective certainty about what an outcome will be does not negate that unperformed measurements have no outcomes. And, (8) quantum theory is a single-user theory for each of us. We then analyze the Wigner's friend thought experiment in light of the eight tenets and indicate that a still more extended analysis is potentially QBism's surest path to uncovering an ontology to go with quantum theory's normative structure. We conclude with a small discussion of how the philosophy of Maurice Merleau-Ponty may be relevant to this quest.
The interpretation of quantum theory known as QBism argues that many elements of the formalism have a subjective interpretation. At the same time, QBism claims to be a broadly realist programme. This implies that reality in QBism must be somehow founded upon an agent's subjective experiences (measurement outcomes). To make this idea more precise, we propose to interpret QBism's “experiences” as synonymous with the concept of “perceived phenomena” in phenomenology. This suggests an approach to ontology in which objects can only be physically real if they are in principle observable. But what does “observable” mean? Are atoms, electromagnetic fields, quantum states, or probabilities observable? Here we discuss the different answers to this question given by QBists and phenomenologists, and attempt to reconcile them.
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.
This is an attempt to clarify certain concepts related to a debate on the interpretation of quantum mechanics, a debate between Khrennikov on the one hand and Stacey and Schack on the other hand. Central to this debate is the notion of quantum probabilities. I first take up the probability concept in the QBist school, as seen from my point of view, and then give my own arguments for the Born formula for calculating quantum probabilities. In that connection, I also sketch some consequences of my approach toward the foundation and interpretation of quantum theory. I discuss my general views on QBism as a possible alternative interpretation of quantum mechanics before I give some final remarks.
At the intersection of the foundations of statistics and the foundations of quantum theory, one comes across a hotly-debated question: what are the probabilities in quantum theories? Do they all reflect the subjective opinions of various agents, or do some of them reflect objective features of the world? One answer—Lewisian dualism, a view that takes some quantum probabilities to be subjective and others to be objective—has gained near-consensus among philosophers of science. However, our most sophisticated defense of this view (due to Deutsch, Wallace, Saunders, Myrvold, Greaves, and others) has two significant problems. First, it requires a very particular approach to the measurement problem (namely, the Everett interpretation). Second, it relies on the pragmatic goals of scientists (e.g., their aim to avoid losses in bets) rather than their epistemic goals (e.g., their aim to accurately describe the world). I give a new defense of dualism that rectifies both of these problems. I generalize the Deutsch-Wallace argument to defend the objective probabilities in a host of realist approaches to measurement, and I modify the accuracy-dominance argument for probabilism to defend the subjective probabilities in these approaches. I also critically examine several previous attempts to interpret all quantum probabilities subjectively.
BACKGROUND: Signs and symptoms of dis-ease are considered observable manifestations of an immaterial Vital Force. Likewise, experimental results on quantum systems are thought to indicate the presence of something that does not show up. Consequently, the discourse of conventional quantum theory (CQT) - with non-locality and entanglement being objective (i.e., ontic) facets of reality - has been considered a useful metaphor for the therapeutic process (TP) in homeopathy/CAMs. Thus, Patient-Practitioner-Remedy (PPR) entanglement postulated an ontic non-local interaction between patient (Px), practitioner (Pr), and potentised medicine/curative procedure (Rx), resulting in the patient's "journey to cure." QBism is a new epistemic interpretation of quantum theory. Rooted in the subjectivity of Bayesianism, QBism refutes the notion that the quantum state of a system is a separate ontic property of reality. In QBism, non-locality and entanglement are considered an agent's "subjective degrees of belief," i.e., they are personally epistemic. OBJECTIVE: To examine whether previous CQT-based entanglement metaphors for the therapeutic process need re-evaluation in the light of QBism. METHOD: Px and Rx quantum states/wavefunctions - ΨPx, and ΨRx - are reinterpreted in QBist terms. Unlike CQT, this means each quantum state/wavefunction is postulated to represent only the local subjective "degrees of belief" of an agent who in this case, is the Pr. RESULTS AND CONCLUSION: Compared to earlier CQT quantum entanglement metaphors, QBism's interpretation of the probabilities inherent in the Px and Rx quantum state/wavefunctions are Bayesian and subjective. Their resulting highly personal epistemology makes them more aligned with (and therefore potentially more useful to) how practitioners might experience the evolution of the TP. Also, because QBism predicts non-locality and entanglement can only be subjective properties of a practitioner's own beliefs, the overall significance of previous ontic non-local CQT-based entanglement metaphors for the TP is questioned.