QBism, Polishing Some Points

TL;DR

This paper clarifies QBism's core principles, emphasizing subjective probabilities, the normative role of the Born Rule, and personal measurement outcomes, contrasting it with other interpretations and exploring its ontological implications.

Contribution

It articulates and clarifies three fundamental tenets of QBism, contrasting it with other quantum interpretations and exploring its ontological and philosophical implications.

Findings

QBism treats the Born Rule as normative, guiding decision-making.

Quantum probabilities are subjective and do not dictate nature's behavior.

Quantum measurement outcomes are personal experiences for the agent.

Abstract

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.