סמינר בחומר מעובה: Thermodynamic Analogies Out-of-Equilibrium: Fluctuations and Effective Temperatures

To what extent can concepts and tools from equilibrium statistical physics be applied to systems far from equilibrium? In this talk, I address this question by exploring the statistical interpretation of temperature beyond thermal equilibrium.

I will present an experimental study examining the thermodynamic properties of an inherently athermal system: a macroscopic harmonic probe driven into nonequilibrium steady-states by random, inelastic collisions with surrounding active walkers (bristle-robots). We test the robustness of the effective temperature concept by comparing distinct, independently motivated definitions: a generalized fluctuation–dissipation relation, a kinetic temperature, and a steady-state work fluctuation-relation. Our experiments reveal that, under specific conditions, these distinct measures coincide over a broad range of system configurations, yielding a consistent and well-defined effective temperature.

Finally, I will discuss a new, nonlinear fluctuation–dissipation test capable of identifying non-Markovian dynamics, and demonstrate its validation (and breakdown) in our experimental system.