Not so fast, College of France says Chu's physics is "unsound."

They are not talking about global warming. ;-)

"Atom interferometers allow the measurement of the acceleration of freely falling atoms with respect to an experimental platform at rest on Earth’s surface. Such experiments have been used to test the universality of free fall by comparing the acceleration of the atoms to that of a classical freely falling object. In a recent paper, Mu ?ller, Peters and Chu [A precision measurement of the gravitational redshift by the interference of matter waves, Nature 463, 926-929 (2010)] argued that atom interferometers also provide a very accurate test of the gravitational redshift (or universality of clock rates). ... As such an alternative has not been proposed to date, we conclude that the interpretation of atom interferometers as testing the gravitational redshift is unsound."
http://arxiv.org/pdf/1012.1194v1