Dark matter, dark energy, gravitational lensing and the formation of structure in the universe

The large-scale structure of the universe and its statistical-properties can reveal many aspects of the physics of the early universe as well as of its matter. content during the cosmic history. Numerous observations, based to a large extent on large scale structure data, have given us a concordant picture of the energy and matter content in the universe.. In view of these results the existence of dark matter has been firmly established although it still evades attempts at direct detection. An even more challenging puzzle is, however, yet to be explained. Indeed the model suggested-by the observations is only viable with the presence of a 'dark energy', an ethereal energy associated with the cosmological vacuum, that would represent about two-thirds of the total energy density of the universe. Although strongly indicated by observations, the existence of this component is nonetheless very uncomfortable from a high-energy physics point of view. Its interpretation is a matter of far reaching debates. Indeed, the phenomenological manifestation of this component can be viewed as a geometrical property of large-scale gravity, or as the energy associated with the quantum field vacuum, or else as the manifestation of a new sort of cosmic fluid that would fill space and remain unclustered. Low redshift detailed examinations of the geometrical or clustering properties of the universe should in all cases.' help clarify the true nature of the dark energy. We present methods that can be used in the future for exploring the low, redshift physical properties of the universe. Particular emphasis will be placed on the use of large-scale structure surveys and more specifically on weak lensing surveys that promise to be extremely powerful in exploring the large-scale mass,distribution in the universe.