Alladi Ramakrishnan Hall

Physics of Sand: Emergent Behavior in the Macro World

Bulbul Chakraborty

Brandeis University, Massachusetts, USA

Diversity in the natural world emerges from the collective
behavior of large numbers of interacting objects. The origin of
collectively organized structures over the vast range of length scales
from the subatomic to colloidal is the competition between energy and
entropy. Thermal motion provides the mechanism for organization by
allowing particles to explore the space of configurations.

This well-established paradigm of emergent behavior breaks down for
collections of macroscopic objects ranging from grains of sand to
asteroids. In this macro-world of particulate systems, thermal motion
is absent, and mechanical forces are all important. We lack
understanding of the basic, unifying principles that underlie the
emergence of order in this world. In this talk, I will explore the
origin of rigidity of granular solids, and present a new paradigm for
emergence of order in these athermal systems.