Directed Aging and Nature’s Greedy Algorithms

Scientists are customarily taught to understand solid materials by treating them as ideal crystals. This approach, however, becomes untenable in an intrinsically disordered material such as a glass: A crystal is an abysmal starting point for understanding the rigidity or excitations of a glass with no obvious long-range order.

In this lecture, Sidney Nagel will discuss how physicists are working to understand glassy matter. He will explain jamming, an alternative starting point for describing solids where order, rather than disorder, is treated as a perturbation. He will then show how physicists have learned to exploit disorder to create solids with unique, varied, textured and tunable behavior including long-range interactions inspired by the allosteric behavior of proteins. Applying these techniques, however, requires computing the response of each bond between particles. Can such detailed computations be avoided? Because a material has a memory of the conditions under which it was prepared and subsequently aged, scientists can now direct aging using Nature’s (as distinct from a computer’s) so-called greedy algorithms to achieve novel kinds of mechanical functionality.

Nagel is the Stein-Freiler Distinguished Service Professor in Physics at the University of Chicago. He received his Ph.D. from Princeton University. Nagel’s broad research goals have been to understand the physics of disordered systems that are far from equilibrium. This work has led him in a variety of unconventional directions, such as the science of drops, granular materials, and jamming. His research group delves into the physics of why drops splash and how materials can remember the way they have been trained. Some of the photographs taken as part of his research projects are currently in the collection of the Smart Museum on the University of Chicago campus.