Was Galileo Wrong?

Galileo Galilei came up with the Equivalence Principle, a cornerstone theory of modern physics. It basically states that gravity will act on objects the same way, regardless of the composition of the material. So if you drop a grand piano and a sheet of paper from orbit onto the Moon, they would both reach there at the same time. Some scientists however, believe that the acceleration due to gravity, does to some degree, depend on the composition of the material -- and NASA scientists are about to test if Galileo is right, in an experiment that will bounce lasers off the mirrors left on the Moon by the Apollo astronauts. Instead of dropping an object onto the Moon, or dropping objects from the Leaning Tower of Pisa like Galileo did, the NASA scientists will be measuring the "dropping" of the Earth and the Moon onto the Sun.