Quantifying Hidden Order Out of Equilibrium

While the equilibrium properties, states, and phase transitions of interacting systems are well described by statistical mechanics, the lack of suitable state parameters has hindered the understanding of non-equilibrium phenomena in divers settings, from glasses to driven systems to biology. Here we introduce a simple idea which enables the quantification of organization in non-equilibrium and equilibrium systems, even when the form of order is unknown. The length of a losslessly compressed data file is a direct measure of its information content, Ic , which, when the file represents a microstate in equilibrium, is its entropy. I will discuss Ic for some out-of-equilibrium systems, and show that it both identifies ordering and reveals critical behavior in dynamical phase transitions.