Erwin Finlay-Freundlich (29 May 1885 – 24 July 1964) was a German astronomer, a pupil of Felix Klein. He was born in Biebrich, Germany to Friedrich Freundlich and Ellen Finlayson. Freundlich was a working associate of Albert Einstein and introduced experiments for which the general theory of relativity could be tested by astronomical observations based on the gravitational redshift.
After finishing his thesis with Felix Klein at the University of Göttingen in 1910, he became assistant at the Observatory in Berlin, where he became associated with Einstein. During a solar eclipse expedition in 1914 to verify general relativity, World War I broke out and he was interned in Russia. After the war, he was engaged in construction of a solar observatory in Potsdam, the Einsteinturm, and he was director of the Einstein-Institut. In 1933 Hitler came to power and Freundlich was forced to leave Germany; he had a Jewish grandmother and his wife was Jewish. He was appointed professor at the University of Istanbul, which was reformed by Kemal Atatürk with the help of many German scholars. In 1937 he left Istanbul to take up the post of professor of astronomy at the Charles University of Prague, but this appointment was terminated by the German occupation. On the recommendation of Arthur Stanley Eddington he went to St. Andrews University in Scotland. From 1951 to 1959 he was John Napier professor of Astronomy. On his retirement he returned to his native town Wiesbaden and was appointed professor at the University of Mainz. Freundlich died in Wiesbaden, Germany.
Freundlich researched the deflection of light rays passing close to the Sun. He proposed an experiment, during an eclipse, to verify the validity of Einstein's theory of general relativity. Freundlich's demonstration would have proven Newton's theories incorrect. He did conduct inconclusive tests on the prediction by Einstein's theory of gravitation-induced red shift of spectral lines in the Sun, using the solar observatories he had constructed in Potsdam and Istanbul. In 1953 he proposed with Max Born an alternative explanation of the red shifts observed in galaxies by a tired light model.
- Erwin Freundlich: Die Grundlagen der Einsteinschen Gravitationstheorie. Mit e. Vorw. von Albert Einstein. - Berlin : Springer, 1916. - 64 S. ; 8
- Erwin Finlay-Freundlich Über die Rotverschiebung der Spektrallinien und Max Born: Theoretische Bemerkungen zu Freundlichs Formel für die stellare Rotverschiebung - Göttingen : Vandenhoeck & Ruprecht, 1953. - S. 96 - 108 ; 4; (Nachrichten der Akademie der Wissenschaften in Göttingen ; Jg. 1953, Nr. 7)
- Klaus Hentschel: The Einstein Tower An Intertexture of Dynamic Construction, Relativity Theory, and Astronomy, Stanford University Press, Stanford 1997.
- School of Mathematics and Statistics. "Erwin Finlay Freundlich". University of St Andrews, Scotland.
- Erwin Freundlich at the Mathematics Genealogy Project