"In his doctoral dissertation, Glen worked with his advisor, Robert Pound, to verify Albert Einstein's prediction that gravity can change the frequency of light. This experiment is widely considered to have started an era of precision tests of General Relativity."--SOURCE: Michalak, R. "Glen Rebka." Physics Today Obituaries. 16 Jan 2015 (http://dx.doi.org/10.1063/PT.5.6123, accessed 2018-02-27).