Dark Energy

The discovery ten years ago that the expansion of the Universe is accelerating put in place the last major building block of the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark energy. At the same time, it posed one of the most profound mysteries in all of science, with deep connections to both astrophysics and particle physics. Cosmic acceleration could arise from the repulsive gravity of dark energy -- for example, the quantum energy of the vacuum -- or it may signal that General Relativity breaks down on cosmological scales and must be replaced. The Dark Energy Survey is a new project currently under construction designed to provide key observational probes that will shed light on this enigma in the coming years.

[in part from Frieman, Turner, Huterer http://arxiv.org/abs/0803.0982]