GBAR experiment
GBAR (Gravitational Behaviour of Anti hydrogen at Rest), AD-7 experiment, is a multinational collaboration at the Antiproton Decelerator of CERN. The GBAR project aims to measure the free-fall acceleration of ultra-cold neutral anti-hydrogen atoms in the terrestrial gravitational field. By measuring the free fall acceleration of anti-hydrogen and comparing it with acceleration of normal hydrogen, GBAR is testing the equivalence principle proposed by Albert Einstein.