The strong experimental evidence for inflation and dark energy leads to deep questions in cosmology that require understanding quantum gravity on de Sitter spacetime and its decays. In this seminar we will present our proposal for a complete theoretical framework for cosmology. The strategy is to generalize AdS/CFT to the cosmological case by adding ingredients to the gravity side that uplift the vacuum energy. As a result, the physics inside an observer patch is formulated holographically in terms of a unitary and Lorentzian low energy theory in one fewer dimension. We will discuss the essential features of this class of quantum field theories, which turn out to be as special as CFTs. Our approach explains the microscopic origin of the de Sitter entropy and suggests a surprising connection between gauge theories with magnetic flavors and cosmological spacetimes.