Fundamental limitations to high-precision tests of the universality of free fall by dropping atoms


Anna M. Nobili

(Physical Review A, 11 February 2016)

This work is dedicated to Professor Erseo Polacco, who contributed to it in numerous discussions and passed away before its completion

High-precision tests of the universality of free fall: can cold atoms compete with macroscopic masses?

The Microscope satellite will fly this April to test to 1 part in 10^15 (100-fold improvement) whether two bodies of different composition are equally accelerated from Earth. Evidence of a violation would signal that either General Relativity needs fixing, or a new force of nature has been found. Either way, it would be a scientific revolution. No matter how rigorous the experiment, such a far reaching result would need confirmation.

Cold-atom drop tests promise very high precision. A paper recently published on Physical Review A (Fundamental limitations to high-precision tests of the universality of free fall by dropping atoms) investigates the effects of initial condition errors and demonstrates that as cold-atom experiments try to reach 10^-15 they hit the uncertainty limits of Heisenberg’s principle because of the negligible number of atoms compared to Avogadro’s number. Precision of 10^-15 and beyond requires macroscopic mass experiments.

The author is the principal investigator of the "Galileo Galilei” (GG)  satellite experiment. Like Microscope, GG is limited by thermal noise at room temperature, but it can aim at 100 times better precision (down to 10^-17) thanks to up-conversion of the signal to higher frequency where thermal noise is lower.

GG: space test of the universality of free fall and the weak equivalence principle to 10^-17

Last edited, Febriary 2016