Entropy fluctuations reveal microscopic interactions

A key element of thermodynamics is small entropy fluctuations away from local maxima at equilibrium. These fluctuating entropy decreases become proportionally larger as the volume decreases within some thermodynamic system. Lessened entropy indicates the formation of organized fluctuating mesoscopic structures. These structures depend upon the microscopic interactions present among the atomic constituents of the system. Entropy fluctuations may be represented by a thermodynamic information metric yielding directly a thermodynamic Ricci curvature scalar R. R is a thermodynamic invariant that is a measure of mesoscopic structure formation within the system. In my talk, I discuss the calculation and the physical interpretation of R in several scenarios: fluid systems, including supercooled liquid water, simple solids, spin systems, quantum fluid models, the quark-meson plasma, and black hole thermodynamics. This range of applications offers a strong argument for the effectiveness of R within thermodynamics.