## Richard Schwartz, Brown University

100 degrees worth of periodic billiard trajectories

**
Thursday March 23, 4:00PM,
Herman Brown 227**
The Triangular Billiards Problem, which is about 200 years old, asks if every triangular shaped billiard table has a periodic billiard path. The answer is known to be "yes" for acute triangles, right triangles, and triangles whose angles are rationally related to pi. So far not much is known about the case of (irrational) obtuse triangles. In this talk I will explain my computer-aided proof that a triangle has a periodic billiard path provided all its angles are at most 100 degress. Along the way I will demonstrate McBilliards, a graphical user interface written by myself and Pat Hooper, which shows the theorem in action.