The third Sloan Digital Sky Survey (SDSS-III) is approximately one quarter of the way through a survey of one million distant galaxies in a quest to build a three-dimensional map on the outer reaches of our universe.
The analyses announced today are based on the Baryon Oscillation Spectroscopic Survey (BOSS) experiment attached to the SDSS 2.5m telescope at Apache Point, New Mexico.
The BOSS experiment has been used to dramatically increase the level of knowledge. "The result is phenomenal," says Will Percival, a professor at the University of Portsmouth in the United Kingdom, and one of the leaders of the analysis team. "We have only one-third of the data that BOSS will deliver, and that has already allowed us to measure how fast the Universe was expanding six billion years ago - to an accuracy of two percent."
The Royal Astronomical Society's press release to coincide with the announcement of the findings asks, "What could be the cause of this accelerating expansion? The leading contender is a strange property of space dubbed "dark energy." Another explanation, considered possible but less likely, is that at very large distances the force of gravity deviates from Einstein's General Theory of Relativity and becomes repulsive." Most researchers shy away from the gravity proposal and instead seek to embrace the concept of dark energy as a means of accounting for the every increasing rate of expansion.
A clear outcome of the experiment was the observation that closer objects (and thus providing more recent data) were expanding more quickly than older and more distant objects.
"There's been a lot of talk about using galaxy maps to find out what's causing accelerating expansion," says David Schlegel of the U.S. Department of Energy's Lawrence Berkeley National Laboratory, the principal investigator of BOSS. "We've been making a map, and now we're using it - starting to push our knowledge out to the distances when dark energy turned on."
Of course these results merely confirm the presence of a bigger question - what is dark energy and what caused it to "turn on" as Schlegel puts it.
On this topic, there is still no news.