For the past five-billion years, the expansion of the universe has been powered by a mysterious repulsive force known
as "dark energy." Now, thanks to a new technique for measuring the three-dimensional structure of the distant universe,
scientists in an international team within the Sloan Digital Sky Survey (SDSS-III), including an astronomer at
Penn State University, have made the first measurement of the rate of this cosmic expansion as it was just
three-billion years after the Big Bang.