Relativity of Observation: Operational Intensive Variables in Nonequilibrium Thermodynamics

TL;DR

This paper develops a framework for understanding and measuring intensive variables in nonequilibrium thermodynamics through operational protocols, emphasizing their local and context-dependent nature.

Contribution

It introduces a method to define and measure intensive variables operationally in nonequilibrium states using local reciprocity and continuous device adjustments.

Findings

Onsager reciprocity holds locally in the proposed framework

Operational definitions of intensive variables can be extended to nonequilibrium states

Measurement protocols enable direct inference of Lagrange multipliers

Abstract

We formulate nonequilibrium thermodynamics in which intensive variables acquire operational meaning through measurement protocols consistent with local reciprocity. Using physical equilibrium as a reference, conjugate observables are constructed by continuously adjusting devices along the local tangent space of the statistical manifold. In this relativity of observation, Onsager reciprocity holds locally, allowing inference-based Lagrange multipliers to be directly measured. This provides a systematic method to extend operational definitions of intensive variables to nonequilibrium states, highlighting their context-dependent nature and offering a concrete experimental strategy.