Paul Chaikin, NYU, Title: “Random to Ordered Packings: From Candies to Monster Crystals from Space.”

Описание: The Physics Department is pleased to present a colloquium featuring Paul Chaikin, New York University, on Monday, April 21, 2025.

Title: “Random to Ordered Packings: From Candies to Monster Crystals from
Space.”

Abstract: The densest packing of spheres, although known for millennia to be a Face-Centered Cubic (FCC) crystal with volume fraction φFCC ~0.74, has only recently been proven mathematically (2014). An equally ancient problem is “Random Close Packing”, RCP, the densest packing of spheres poured into a jar described in Biblical times (Luke 6:38, KJV) as, “pressed down, and shaken together, and running over”. RCP has escaped a noncontroversial definition although many experiments and simulations agree to a value φRCP ~0.64. We have found that a simple model, “Random Organization”, RO, exhibits a dynamical phase transition between absorbing, ‘dead’, and active states that appears to have RCP as its critical endpoint. Invented to understand a reversible to irreversible transition in sheared colloids, RO finds RCP with emergent properties such as, randomness, isotropy, isostaticity, hyperuniformity and jamming. To close the book on the crystalline phase, we grew a single crystal on the international space station which found that FCC is the equilibrium structure as compared to the hexagonal close packed and the many other structures with the same φmax =0.74…