Clocking an accelerating universe: First results from BOSS

Clocking an accelerating universe: First results from BOSS: First spectroscopic results from BOSS give the most detailed look yet at the time when dark energy turned on some six billion light years ago, as the expansion of the universe was slipping from the grasp of matter's mutual gravitational attraction, and expansion began to accelerate.

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BOSS measures the three-dimensional clustering of galaxies at various redshifts, revealing their precise distance, the age of the universe at that redshift, and how fast the universe has expanded. The measurement uses a "standard ruler" based on the regular variations of the temperature of the cosmic microwave background, which reveal variations in the density of matter in the early universe that gave rise to the later clustering of galaxies and large-scale structure of the universe today. (Credit: Credit: Eric Huff, the SDSS-III team, and the South Pole Telescope team. Graphic by Zosia Rostomian)

ScienceDaily (Mar. 30, 2012) — Some six billion light years ago, almost halfway from now back to the big bang, the universe was undergoing an elemental change. Held back until then by the mutual gravitational attraction of all the matter it contained, the universe had been expanding ever more slowly. Then, as matter spread out and its density decreased, dark energy took over and expansion began to accelerate.

Today BOSS, the Baryon Oscillation Spectroscopic Survey, the largest component of the third Sloan Digital Sky Survey (SDSS-III), announced the most accurate measurement yet of the distance scale of the universe during the era when dark energy turned on.
"We've made precision measurements of the large-scale structure of the universe five to seven billion years ago -- the best measure yet of the size of anything outside the Milky Way," says David Schlegel of the Physics Division at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), BOSS's principal investigator. "We're pushing out to the distances when dark energy turned on, where we can start to do experiments to find out what's causing accelerating expansion."