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Beyond QBism with Ontology of Knowledge iss. 20200418

Jean-Louis Boucon

Published Jan 1, 2020• 0 citations
OpenAlex

Abstract

[issue 20211210] Qbism (quantum bayesism) is a philosophical interpretation of quantum mechanics (QM) that places the agent and its expectations at the heart of theory. The QBists advocate a "subjectivist" interpretation of probabilities that allows to understand the quantum laws of Born and to eliminate certain enigmas of interpretation of the QM going "beyond" the interpretation of Copenhagen. The Ontology of Knowledge (OK) is in agreement with the main ideas of the Qbism. For the OdC indeed: -The agent is the focal point of the representation -Representation is specific to the agent -There are no "states of the world" but only "states of knowledge" -There is no probability of evolution of the "state of the world" but only probabilities, for the subject, of evolution of his Knowledge. -These probabilities lead to the future actions and experiences of the agent. The aim of this article is to propose, according to the OdC, ways for an extension of the explanatory power of the QBism.

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[issue 20211210] Qbism (quantum bayesism) is a philosophical interpretation of quantum mechanics (QM) that places the agent and its expectations at the heart of theory. The QBists advocate a "subjectivist" interpretation of probabilities that allows to understand the quantum laws of Born and to eliminate certain enigmas of interpretation of the QM going "beyond" the interpretation of Copenhagen. The Ontology of Knowledge (OK) is in agreement with the main ideas of the Qbism. For the OdC indeed: -The agent is the focal point of the representation -Representation is specific to the agent -There are no "states of the world" but only "states of knowledge" -There is no probability of evolution of the "state of the world" but only probabilities, for the subject, of evolution of his Knowledge. -These probabilities lead to the future actions and experiences of the agent. The aim of this article is to propose, according to the OdC, ways for an extension of the explanatory power of the QBism.
QBism is a recently developed version of Quantum Bayesianism. QBists think that the primitive concept of experience is the central subject of science. QBism refuses the idea that the quantum state of a system is an objective description of this system. It is a tool for assigning a subjective probability to the agent's future experience. So quantum mechanics does not directly say something about the "external world". A measurement (in the usual sense) is just a special case of what QBism calls experience and this is any action done by any agent on her external world. The result of the measurement is the experience that the agent gets from her action on her personal world. For Qbists, this way of seeing the measurement helps rejecting any non-local influences. We will examine if these claims are robust and will show that a certain number of issues needs to be clarified in order to get a coherent picture. Depending on the way these necessary clarifications are made, the global image given by Qbism can vary from pure instrumentalism to interpretations making the observer play a radical role.
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 pursues the real by first eliminating the elements of quantum theory too fragile to be ontologies on their own. Thereafter, it seeks an "ontological lesson" from whatever remains. Here, we explore this program by highlighting three tenets of QBism. First, the Born Rule is a normative statement. It is about the decision-making behavior any individual agent should strive for, not a descriptive "law of nature." Second, 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, which implies a more radical kind of indeterminism in quantum theory than other interpretations understand. Third, quantum measurement outcomes just are personal experiences for the agent gambling upon them. Thus all quantum measurement outcomes are local in the sense of the agent enacting them. Through these tenets, we explain four points better than previously: 1) how QBism contrasts with Bohr's concern over unambiguous language, 2) how QBism contrasts with the Everett interpretation, 3) how QBism understands the meaning of Bell inequality violations, and 4) how QBism responds to Wigner's "suspended animation" argument. Finally, we consider the ontological lesson of the tenets and ask what it might mean for the next one hundred years of quantum theory and humankind more generally.
Quantum Bayesianism, or QBism, is a recent development of the epistemic view of quantum states, according to which the state vector represents knowledge about a quantum system, rather than the true state of the system. QBism explicitly adopts the subjective view of probability, wherein probability assignments express an agent’s personal degrees of belief about an event. QBists claim that most if not all conceptual problems of quantum mechanics vanish if we simply take a proper epistemic and probabilistic perspective. Although this judgement is largely subjective and logically consistent, I explain why I do not share it.
A new interpretation of quantum mechanics, the interpretation which became popular in XXI, has been taken under consideration. This is the quantum baysinism (QBism) which may be taken as an extrapolation of the baysian philosophy of probability over the interpretation of quantum mechanics. The baysian philosophy of quantum mechanics has been compared with the Copenhagen interpretation of quantum mechanics, the interpretation which can been treated as standard as it is represented in the main textbooks. In contrast to the Copenhagen interpretation which proceeds from the triplets – nature, apparatus and observer (agent), QBism emphasizes the conscious of the observer: the quantum state is the observer’s state, and by means of the quantum conceptual technique the observer constructs his/her own image of quantum processes. By means of measurement the observer updates his/her quantum state, the measuring apparatus being an extension of the observer’s sensuality. From the point of the QBism’s view the phenomenon of decoherence which is widely discussed in the contemporary literature is not essential for the theory of measurement in quantum mechanics. The decoherence explains why the macroscopic phenomena don’t expose the interference behavior which is characteristic for quantum superposition. From the historicо-philosophical point of view Qbism can be traced back to American instrumentalism and operationalism.
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.