What is ontic and what is epistemic in the Quantum Mechanics of Spin?

TL;DR

This paper extends Entropic Dynamics to include spin, creating a realist { extbackslash psi}-epistemic model where particles have definite positions and a discrete spin variable, clarifying the ontic and epistemic aspects of quantum spin.

Contribution

It develops a spin-inclusive ED framework that models quantum spin with clear ontic and epistemic distinctions, linking probabilities to physical entities.

Findings

The model reproduces the Pauli equation for spin dynamics.

Transformations generators have explicit epistemic interpretation.

The concept of 'spin' is clarified as non-spinning in this framework.

Abstract

Entropic Dynamics (ED) provides a framework that allows the reconstruction of the quantum formalism by insisting on ontological and epistemic clarity and adopting entropic methods and information geometry. Our present goal is to extend the ED framework to account for spin. The result is a realist {\psi}-epistemic model in which the ontology consists of a particle described by a definite position plus a discrete variable that describes Pauli's peculiar two-valuedness. The resulting dynamics of probabilities is, as might be expected, described by the Pauli equation. What may be unexpected is that the generators of transformations -- Hamiltonians and angular momenta including spin, are all granted clear epistemic status. To the old question `what is spinning?' ED provides a crisp answer: nothing is spinning.