Dresden 2026 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 47: Statistical Physics: General I

DY 47.1: Talk

Thursday, March 12, 2026, 09:30–09:45, ZEU/0114

Microcanonical ensemble out of equilibrium — •Roman Belousov¹, Jenna Elliott^1,2, Florian Berger³, Lamberto Rondoni^4,5, and Anna Erzberger^1,2 — ¹European Molecular Biology Laboratory (EMBL), Heidelberg, Germany — ²Heidelberg University, Heidelberg, Germany — ³Utrecht University, Utrecht, The Netherlands — ⁴Politecnico di Torino, Turin, Italy — ⁵Istituto Nazionale di Fisica Nucleare (INFN), Turin, Italy

The microcanonical ensemble serves as the fundamental representation of equilibrium thermodynamics in statistical mechanics by counting all possible realizations of a system’s states. Ensemble theory connects this idea with probability and information theory, leading to the notion of Shannon-Gibbs entropy and, ultimately, to the principle of maximum caliber describing trajectories of systems—in and out of equilibrium. While the latter phenomenological generalization reproduces many results of nonequilibrium thermodynamics, its physical justification remains an open area of research. What is the microscopic origin and physical interpretation of this variational approach? What guides the choice of relevant observables? We address these questions by extending Boltzmann’s method to a microcanonical caliber principle. Thereby we systematically develop generalized local detailed-balance relations, clarify the statistical origins of inhomogeneous transport, and provide an independent derivation of key equations from stochastic thermodynamics. This approach introduces a dynamical ensemble theory, which we verify in numerical simulations of spatially extended, driven, and active systems.

Keywords: Ensemble theory; Nonequilibrium thermodynamics; Nonequilibrium statistical mechanics; Transport phenomena; Active systems