Pound–Rebka experiment

The Pound–Rebka experiment, conducted by physicists Robert Pound and Glen A. Rebka in 1959 at Harvard University, was a pivotal experiment designed to test the predictions of Einstein's theory of general relativity, specifically the gravitational redshift effect. In essence, the gravitational redshift effect posits that light emitted from a source in a gravitational field (such as the Earth) will lose energy as it climbs out of that field.