The other entropy.

Granular materials are not in thermodynamic equilibrium. Nevertheless, concepts borrowed from equilibrium statistical mechanics are extensively used to characterise granular systems. One often-invoked concept is the so-called granular entropy. In this paper, we consider what it would take to compute granular entropy numerically. Our focus is the analogy (or, more accurately, lack thereof) between statistical mechanical ensembles, as used in Monte Carlo simulations of thermal systems, and preparation protocols used in the generation of granular packings. Attempts to phrase the description of granular media in ‘thermal’ Monte Carlo language reveal some awkward problems. Whilst some of these problems had been reported in the existing literature, the present perspective yields new insights. [ABSTRACT FROM AUTHOR]