The True Size of the Universe: Astronomers' Breakthrough in Measuring Rate of Expansion

Since the universe began, it has been expanding. Tracking that expansion could tell scientists quite a bit about the physics of our world; yet it's difficult to be able to precisely measure it. Now, though, researchers have made novel measurements using BOSS, the Baryon Oscillation Spectroscopic Survey, when the universe was a mere three billion years old.

BOSS is the largest component of the Sloan Digital Sky Survey. It uses quasars to map density variations in intergalactic gas at high redshifts, and traces the structure of the young universe. This, in turns, allows BOSS to chart the history of the universe's expansion in order to show scientists a little bit more about the nature of dark energy, and allow them to take precise measurements.

The latest findings combine two separate techniques. Together, these methods establish an expansion rate of the universe of 68 kilometers per second per million light years at redshifts 2.34; the accuracy is an unprecedented 2.2 percent.

"This means if we look back to the universe when it was less than a quarter of its present age, we'd see that a pair of galaxies separated by a million light years would be drifting apart at a velocity of 68 kilometers a second as the universe expanded," said Andreu Font-Ribera, one of the researchers, in a news release. "The uncertainty is plus or minus only a kilometer and a half per second."

In fact, about three years ago BOSS used 14,000 quasars to help creature the largest 3D maps of the universe. Then two years ago, BOSS used 48,000 quasars to detect baryon acoustic oscillations (BAO) in these maps. Now, the scientists have made extremely precise measurements of BAO with even more quasars.

"It's the most precise measurement of the Hubble parameter at any redshift, even better than the measurement we have from the local universe at redshift zero," said Font-Ribera in a news release. "These results allow us to study the geometry of the universe when it was only a fourth its current age. Combined with other cosmological experiments, we can learn about dark energy and put tight constraints on the curvature of the universe-it's very flat!"

The findings are published in the Journal of Cosmology and Astropartical Physics and Astronomy & Astrophysics.