Symplectic Tiling Billiards, Planar Linkages, and Hyperbolic Geometry

Abstract

In this paper I will unite two games, symplectic billiards and tiling billiards. The new game is called symplectic tiling billiards. I will prove a result about periodic orbits of symplectic tiling billiards in a very special case and then show how this result combines with the construction in Thurston's paper {\it Shapes of Polyhedra\/} to give hyperbolic structures on moduli spaces of planar equilateral polygons. One corollary is that the configuration space of the hexagonal planar linkage with unit-length rods (modulo isometry) has an algebraically defined hyperbolic structure in which it is a $10$-cusped hyperbolic $3$-manifold that is tiled by $15$ regular ideal octahedra. The $10$ cusps correspond to the $10$ maximally degenerate configurations.