Understanding the High Energy Limit of Quantum field Theory

Quantum field theory has proven to be the most powerful and successful tool in physics, yet despite a century of progress many problems remain open. Some of these problems are just coming to light, e.g. non-Fermi liquids, while others have been around a while but are still open, such as the one I will discuss in this talk. Namely, the high energy limit, which is the regime where the center of mass energy is hierarchily larger than the momentum exchange. This limit is of particular interest in Yang-Mills and gravity where it plays an important role both phenomenlogically, and formally. In YM theory this limit dominates the cross section at colliders, while in gravity it leads to black hole formation. In both theories our understanding of this ``Regge” limit is still lacking, as naive calculations seem to lead to a breakdown of unitarity. In this talk i will discuss how recent progress in effective field theory has led to new insights and results.