Constructing a Theory for Amorphous Solids

Amorphous solids are disordered assemblies of atoms or larger particles that nonetheless have a rigid structure. Examples include glass, cement, compacted sand, and even yogurt or chocolate mousse (Fig. 1). At first sight, these materials may appear to have little in common. But amorphous solids share many mechanical properties, and physicists have long been interested in finding a theory that predicts the materials’ behavior in terms of their microstructure in a unified way. Unlike crystalline solids, however, the rigidity of amorphous solids is not associated with a thermodynamically stable, stress-free microstructure, so researchers have had to turn to novel theoretical approaches. A pair of papers from Eric DeGiuli of École Normale Supérieure in Paris [1, 2] now marks progress toward the goal of a unifying theory. Building on recent theories for glasses and granular materials, DeGiuli presents a general field theory for amorphous solids and uses it to predict how they transmit stress.