Abstract
This latest lecture discusses the prospects in the near future for making progress on the dark energy problem. Satellite missions will be devoted to this problem, such as ESA's Euclid satellite, to be launched in 2020, or NASA's Wide Field Infrared Survey Telescope (WFIRST) mission, dedicated to dark energy and exoplanets (~ 2025-2030?). On the ground, the LSST, or Large Synoptic Survey Telescope, an 8 m wide-field telescope located in Chile, and the SKA, or Square Kilometer Array, an array of low-frequency radio antennas, located in both Australia and South Africa, depending on the observation frequency, between 2 cm and 6 m wavelength. The five main tools for obtaining the equation of state for dark energy, and thus its nature, are weak lenses (cosmic shear), type Ia supernovae, BAOs, Redshift Space Distortions (or RSDs), and galaxy clusters.
On the other hand, the presence of structures as a function of time will make it possible to measure the rate of their growth, and thus test for modified gravity. It is also possible to better understand the origin of cosmic structures, and thus test for inflation, by improving by a factor of 20 the spectral index of the echelle distribution, or the amplitude of the power spectrum, non-gaussianities, etc. All cosmological parameters are entangled in several models, and it is important to measure more precisely the Hubble constant, whose value derived from the cosmological microwave background is in tension with the optical determination from cepheids. The SKA will be able to determine this independently, thanks to megamasers in galaxies, for example. The SKA will be able to determine BAOs with tracers that are completely different from optical galaxies (bias towards galaxy clusters), i.e. with gas-rich galaxies, which tend to be found between clusters. LSST will have a very rich variable-domain aspect, mapping the entire sky every three days, and issuing 1 to 2 million alerts per night for variable objects.
