QBism: Subjective Probabilistic Interpretation of Quantum Mechanics

Brigitte Falkenburg, Peter Mittelstaedt

Andrei Yu. Khrennikov

This chapter is devoted to quantum Bayesianism (QBism), the subjective probability interpretation of QM. Creation of such an interpretation is an important step towards unification of applications of the mathematical formalism of QM to physical and to cognitive and sociopolitical systems. QBism can serve to couple the general theory of decision making based on subjective probability with quantum formalism. On the other hand, our quantum-like modeling of sociopolitical processes does not depend on interpretations of QM. Therefore, the reader need not read this chapter, which has a merely foundational value.

Philipp Berghofer

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.

Jacques Pienaar

Andrei Yu. Khrennikov

We discuss the subjective probability interpretation of the quantum-like approach to decision making and more generally to cognition. Our aim is to adopt the subjective probability interpretation of quantum mechanics, quantum Bayesianism (QBism), to serve quantum-like modelling and applications of quantum probability outside of physics. We analyse the classical and quantum probabilistic schemes of probability update, learning and decision-making and emphasize the role of Jeffrey conditioning and its quantum generalizations. Classically, this type of conditioning and corresponding probability update is based on the formula of total probability-one the basic laws of classical probability theory.