Fermilab’s Dark Energy Strategy:

Past, Present, and Future

Josh Frieman

Fermilab and the University of Chicago

In the late 1990's, observations of distant supernovae led to the discovery that the expansion of the Universe is speeding up. Observations over the past decade have confirmed this remarkable finding. For the coming decade, as noted by the recent Astro 2010 Decadal Survey report, understanding the physical origin of cosmic acceleration---is it dark energy or a modification of Einstein's General Relativity?---will be a major focus of research on the Cosmic Frontier. Fermilab astrophysics experiments have played and will continue to play major roles in probing the nature of dark energy and the cause of cosmic acceleration. In this talk, I will review what we have learned about dark energy from the Sloan Digital Sky Survey and other observations. I will provide an overview of the Dark Energy Survey, which will use a powerful new instrument on a four-meter telescope in Chile to carry out a five-year survey, starting in 2012, of 300 million galaxies and thousands of supernovae and that will provide a major advance in constraining dark energy. I will close by looking toward the end of the decade, when a number of projects are poised to go further: LSST on the ground, WFIRST in space, large spectroscopic surveys such as BigBOSS and DESpec, and 21-cm radio surveys.