The Universe as a hologram

String theory is the evolution of theoretical constructions developed during the past century, embracing and extending general relativity and quantum mechanics. One of the lessons of string theory has been the discovery of relationships between seemingly different theories, called dualities. In particular, the gauge/gravity duality postulates that a theory of gravity is equivalent to a quantum field theory in one lower dimension. In this seminar I will explain why imagining the universe as a holographic projection of lower dimensional space-time has radically changed the way we think about fundamental questions in theoretical physics.