Our very own Michael Khanevsky will speak in the geometry seminar on 1st December, at 2pm, in the Salle de Profs (9th floor of building NO). Michael’s title is *Hofer’s metric and length spectrum of symplectic surfaces*. His abstract follows.

In Riemannian geometry the length spectrum is a rich source of invariants of the manifold. In symplectic setting there is no notion of length, hence no possibility to define the usual length spectrum. However one can use Hofer’s metric to define a family of invariants with similar behavior. Pick a ball of a chosen area and translate it by a Hamiltonian isotopy along a given homotopy (or homology) class. The minimal Hofer energy required for such translation can be seen as a substitute for the Riemannian length spectrum. We will discuss estimates for this energy in two-dimensional case.