http://newscenter.berkeley.edu/2010/02/17/gravitational_redshift/

While airplane and rocket experiments have proved that gravity makes clocks tick more slowly — a central prediction of Albert Einstein’s general theory of relativity — a new experiment in an atom interferometer measures this slowdown 10,000 times more accurately than before, and finds it to be exactly what Einstein predicted.

The result shows once again how well Einstein’s theory describes the real world, said Holger Müller, an assistant professor of physics at the University of California, Berkeley.

“This experiment demonstrates that gravity changes the flow of time, a concept fundamental to the theory of general relativity,” Müller said. The phenomenon is often called the gravitational redshift because the oscillations of light waves slow down or become redder when tugged by gravity.

A report describing the experiment appears in the Feb. 18 issue of the journal Nature.