Abstract
More than 95 % of the Universe's content is black or unknown : in addition to the 25 % made up of exotic dark matter, for the last twenty-five years we have known that the expansion is accelerating, due to dark energy which represents 70 % of the content. Astrophysical constraints are obtained with the best probes, supernovae Ia, then gamma-ray bursts, strong gravitational lenses, or gravitational waves emitted by black hole mergers. For the moment, a cosmological constant, as introduced by Einstein, could explain the observations. However, the energy of the quantum vacuum still has a density 50 to 100 orders of magnitude greater than that of the dark energy of the Universe. If dark energy is dynamic, it could be linked to inflation in the early universe. Or should we appeal to a modified gravity, which could also be compatible with quantum mechanics ? There are several attempts : uni-modular gravity, super-symmetry (SUSY), string theory, holography, loop quantum gravity.
