A team of researchers at Stanford University in California have confirmed that the value of g, acceleration caused by gravity, is constant with respect to mass and size. The physicists employed laser cooling to construct an atom interferometer that measured the rate of fall of cesium atoms. They found that the atoms experienced an acceleration that agreed with the g on macroscopic objects to within seven parts in a billion.

The team cooled about 5 x 10⁸ atoms to 1.5 µK, launched them with a series of microwave pulses and measured their rate of descent by observing Raman scattering effects on the initial, superposition state of the super-cooled cesium. The researchers used a Michelson interferometer gravimeter to compare the results against the g of a falling prism, which is governed by classical mechanics.

Steven Chu, the 1997 Nobel laureate who developed the laser-cooled, atomic fountain technique and was a member of the team, said the result challenges the speculation that space-time fluctuations affect gravity at the quantum-mechanical level, a suggestion that followed recent experiments that used a neutron interferometer to measure.