The cosmological constant and entropy problems: mysteries of the present with profound roots in the past

An accelerated universe should naturally have a vacuum energy density determined by its dynamical curvature. The cosmological constant is most likely a temporary description of a dynamical variable that has been drastically evolving from the early inflationary era to the present. In this Essay we propose a unified picture of the cosmic history implementing such an idea, in which the cosmological constant problem is fixed at early times. All the main stages, from inflation and its ("graceful") exit into a standard radiation regime, as well as the matter and dark energy epochs, are accounted for. Finally, we show that for a generic Grand Unified Theory associated to the inflationary phase, the amount of entropy generated from primeval vacuum decay can explain the huge measured value today.