BOSS (the Baryon Oscillation Spectroscopic Survey) has just announced the most accurate measurement yet of the distribution of galaxies between five and six billion years ago. This was the key pivot moment at which the expansion of the universe stopped slowing down due to gravity and started to accelerate instead, due to a mysterious force dubbed “dark energy.”
The nature of this “dark energy” is one of the big mysteries in cosmology today, and scientists need precise measurements of the expansion history of the universe to unravel this mystery — BOSS provides this kind of data.
http://www.eurekalert.org/pub_releases/2012-03/dbnl-caa032912.php