Dark energy and universe models

Since 1998, we've known that the expansion of the Universe is accelerating. As a result of this discovery, made through the observation of Type Ia supernovae, which can be considered as standard candles, the Nobel Prize was awarded to Saul Perlmutter, Adam Riess and Brian Schmidt in 2011. Until then, astronomers were convinced that the expansion was decelerating, slowed down by the Universe's own gravity. Acceleration implies repulsion, not attraction, hence the invention of dark energy, a component whose pressure is a negative function of density. Could this dark energy be the energy of the quantum vacuum, extrapolated to cosmological scales? It soon became clear that this was not the case, as the predicted energy would be 120 orders of magnitude greater than that observed. All observations are fairly compatible with a cosmological constant, but the problem of fine-tuning and remarkable coincidences is hard to explain. The cosmological constant would make it possible to predict the fate of our exponentially expanding Universe, like De Sitter's empty Universe. This exponential expansion bears a striking resemblance to the first phase that occurs in a fraction of a second after the Big Bang: inflation. Inflation is necessary to explain the problem of the horizon and the flatness of the Universe.