 Born in Hamburg, Germany, in 1891, Hans Reichenbach was the second of four children of a half-Jewish but baptized father and a non-Jewish mother. In secondary school and at university he was active in the socialist student movement. From 1910 to 1911 he studied civil engineering at the Technische Hochschule in Stuttgart, and then moved among Berlin, Munich and Göttingen, studying physics, philosophy and mathematics with some of the eminences of the time, including Ernst Cassirer, Max Planck, Arnold Sommerfeld and David  Hilbert.[1]  He wrote his doctoral dissertation largely on his own after the neo-Kantian Paul Natorp would not accept him as his student. After searching for alternative advisors, his dissertation was finally accepted by Paul Hensel, a philosopher, and Max Noether, a mathematician, in 1915 in Erlangen. Reichenbach was conscripted into the army while completing his thesis. He served in the German army signal corps on the Russian front until a serious illness sent him back to Berlin in 1916. He was relieved from active military duty in 1917 to work as an engineer for a firm specializing in radio technology. In Berlin, Reichenbach attended Albert Einstein’s lectures on relativity and statistical mechanics, which influenced him profoundly, and inaugurated a life-long friendship between the two men. He wrote several popular articles defending Einstein, especially in the context of the observations of the solar eclipse of 1919 confirming the predictions of the general theory of relativity. 