In and out of equilibrium

Albert Einstein's work on brownian motion showed how thermal equilibrium could be brought about by work exchanged through thermal fluctuations and viscous dissipation. Glasses are out-of-equilibrium systems in which this exchange happens at widely different timescales simultaneously. Theory then suggests the fascinating possibility that such behaviour may lead to a more general form of thermalization, in which the effective temperature shared by all components differs at each timescale.