The equality of inertial and gravitational mass central to Einstein’s general theory of relativity has been confirmed at unprecedented sensitivities by the MICROSCOPE satellite. Having gathered several thousand orbits’ worth of accelerometer data from two masses in free fall around the Earth, the French mission has found no violation of the equivalence principle at the level of a few parts in a thousand trillion. Mission scientists say that better control of thermal and other noise could boost precision by a further factor of 100, so allowing tests of quantum-gravity theories.
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