Nebula Public Library

We report on a new test of the gravitational redshift and thus of local position invariance, an integral part of the Einstein equivalence principle, which is the foundation of general relativity and all metric theories of gravitation. We use data spanning 1008 days from two satellites of Galileo, Europe’s global satellite navigation system (GNSS), which were launched in 2014, but accidentally delivered into elliptic rather than circular orbits. The resulting modulation of the gravitational redshift of the onboard atomic clocks allows the determination of redshift with high accuracy.