Thermo-Statistics or Topology of the Microcanonical Entropy Surface

TL;DR

This paper explores the topology of the microcanonical entropy surface using geometric methods, demonstrating phase separation and equilibrium properties in non-extensive systems like self-gravitating clouds without needing non-standard thermodynamics.

Contribution

It introduces a geometric framework for understanding microcanonical entropy topology and phase transitions in non-extensive systems, avoiding the need for Tsallis non-extensive thermodynamics.

Findings

Topology of entropy surface relates to phase separation.

Equilibrium configurations include stars, rings, and gases.

Finite systems approach equilibrium with non-decreasing entropy.

Abstract

Boltzmann's principle S(E,N,V...)=ln W(E,N,V...) allows the interpretation of Statistical Mechanics of a closed system as Pseudo-Riemannian geometry in the space of the conserved parameters E,N,V... (the conserved mechanical parameters in the language of Ruppeiner) without invoking the thermodynamic limit. The topology is controlled by the curvature of S(E,N,V...). The most interesting region is the region of (wrong) positive maximum curvature, the region of phase-separation. This is demonstrated among others for the equilibrium of a typical non-extensive system, a self-gravitating and rotating cloud in a spherical container at various energies and angular-momenta. A rich variety of realistic configurations, as single stars, multi-star systems, rings and finally gas, are obtained as equilibrium microcanonical phases. The global phase diagram, the topology of the curvature, as function of energy and angular-momentum is presented. No exotic form of thermodynamics like Tsallis non-extensive one is necessary. It is further shown that a finite (even mesoscopic) system approaches equilibrium with a change of its entropy Delta S\ge 0 (Second Law) even when its Poincarre recurrence time is not large.