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Math Colloquium
Richard Evan Schwartz
Brown University
Title: The Plaid Model and Outer Billiards

Abstract: Outer billiards is a dynamical system in which a point "bounces around" the outside of a convex shape according to rules that are somewhat akin to the ones for ordinary billiards. Even for simple convex shapes like kites (convex quadrilaterals with bilateral symmetry) the trajectories of the points are quite intricate. I will describe a combinatorial model, which I call the plaid model, which predicts the shapes of the trajectories for outer billiards on kites. Along the way, I'll explain (somewhat) how the plaid model shows the existence of unbounded trajectories, resolving what had been one of the central questions about outer billiards.

Date: Friday, October 16, 2015
Time: 4:30 pm
Location: Wean Hall 7500
Submitted by:  Pego
Note: Refreshments at 4:00 pm, Wean Hall 6220.