Abstract:

While cosmological observations now point convincingly to an accelerating Universe, we have no fundamental understanding of the physics driving this expansion: is it a new form of stress-energy with negative pressure, e.g., the cosmological constant, or does it signal a breakdown of General Relativity on large scales? A number of observational probes are being applied to this problem---most prominently supernovae, weak lensing, galaxy clusters, and baryon acoustic oscillations---and a series of increasingly ambitious projects have been proposed to attack it over the next decade. This talk will focus on two projects, one on-going, the other near-term. The first is the SDSS Supernova Survey, a 3-year project now in the final stages of data-taking, which has measured multi-band light curves and spectra for several hundred type Ia supernovae at intermediate redshifts. I will discuss the early results and some of their implications for future supernova cosmology studies. The second is the Dark Energy Survey (DES), a large-area, multi-band imaging survey that will use a new wide-field camera on the 4-meter telescope at Cerro Tololo Inter-American Observatory. Covering 5000 square degrees and beginning in 3 years, DES will employ all four of the above dark energy methods.