Using Galaxies as Yardsticks
Sunday, March 4, 2012
News Feature

Daniel Eisenstein is investigating the universe, using galaxies as his ruler, seeking to understand the cosmos' large-scale structure and confirm theories about the dark energy that drives its expansion.

Eisenstein is a professor of astronomy in the Harvard Astronomy Department and at the Harvard Smithsonian Center for Astrophysics. He also heads a major study of the heavens, the Sloan Digital Sky Survey, which is building the most detailed map of the universe ever made.

Eisenstein has devised a new method to determine galaxies’ positions in order to understand more about the universe and to test theories about how it operates. So far, he said, the galactic positions have confirmed findings from the 1990s that we live in a universe that is not only expanding but accelerating, fueled by the invisible force of dark energy.

“One of the ways of studying dark energy is by making extremely precise measurements of cosmological distance,” Eisenstein said.

His work has its roots in the universe’s earliest beginnings, just after the big bang flung matter outward in an enormous explosion. During the first 400,000 years, sound waves propagated through what was basically a dense, hot cloud of hydrogen atoms and scattered photons of light. These sound waves disturbed matter’s even distribution that resulted from the Big Bang. This perturbation allowed gravity to exert influence by making small clumps of matter into bigger clumps, and large clumps into nebulae — gas clouds that are stellar nurseries — which created stars themselves, solar systems, and the galaxies.