By tracking the moon's location to within 1 centimeter, astronomers have put general relativity, Albert Einstein's theory of gravity, to a stringent new test. The theory stood up. In a separate experiment, physicists reconfirmed Einstein's older predictions on the stretching of time.
While both general relativity and quantum theory so far fit experimental data very well, their incompatibility makes physicists believe that at small scales either one of them or both must be wrong. Scientists constantly work to improve the sensitivity of their experiments to violations that might point to a new "theory of everything."
Astronomers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., have now performed a new analysis of 35 years' worth of data on the moon's distance from Earth, including data they recently collected themselves with centimeter precision. The data tracked the time it took for a laser beam to reach a mirror on the lunar surface—left beh