Tel Aviv University Hello everyone, The next colloquium talk will be held on: Monday, 21/01/2013, 12:15, Schreiber 006, Tel Aviv University. Speaker: Danny Calegari (University of Chicago) Title: Surfaces From Linear Programming. This talk is part of the Blumenthal Lectures in geometry 2013. The abstract is given below. Tea and coffee at 12:00, same room. Hope to see you there. For information about future colloquia, see <http://www.math.tau.ac.il/~ostrover/colloquium/colloq2012.html> Yours, Yaron **************************************************** Abstract: A famous question of Gromov asks whether every hyperbolic group contains a subgroup which is isomorphic to the fundamental group of a closed surface. Surface subgroups play a very important role in many areas of low-dimensional topology, for example in Agol's recent proof that every hyperbolic 3-manifold has a finite cover which fibers over the circle. I would like to describe several ways to build surface subgroups in certain hyperbolic groups. The role of hyperbolicity is twofold here: first, hyperbolic geometry allows one to certify injectivity by *local* data; second, hyperbolic dynamics allows one to use ergodic theory to produce the pieces out of which an injective surface can be built. I would like to sketch a proof of the fact that the extension of a free group associated to a ''random'' endomorphism contains a surface subgroup with probability one. This is joint work with Alden Walker. --------------------------------------------------------- Technion Math Net-2 (TECHMATH2) Editor: Michael Cwikel <techm@math.technion.ac.il> Announcement from: <ostrover@post.tau.ac.il>