Invited review for Annual Reviews of Astronomy and Astrophysics
arXiv:0803.0982v1

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DARK ENERGY AND THE ACCELERATING UNIVERSE

Joshua A. Frieman

Center for Particle Astrophysics, Fermi National Accelerator Laboratory, P. O. Box 500, Batavia, IL 60510;
Kavli Institute for Cosmological Physics, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637; email: frieman@fnal.gov

Michael S. Turner

Kavli Institute for Cosmological Physics, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637; email: mturner@uchicago.edu

Dragan Huterer

Department of Physics, University of Michigan, 450 Church St., Ann Arbor, MI, 48109; email: huterer@umich.edu

Key Words: cosmology, cosmological constant, supernovae, galaxy clusters, large-scale structure, weak gravitational lensing

Abstract. 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. We review the present observational evidence for cosmic acceleration and what it has revealed about dark energy, discuss the various theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that will shed light on this enigma in the coming years.

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