A Brill Calendar: September 25

Few universities considered themselves peers to Leyden University during the Interbellum when it came to theoretical physics.

And few professors of Leyden in that branch of science were as important to the ‘Praesidium Libertatis’ as the Austrian physicist Paul Ehrenfest (Vienna, January 18, 1880 – Amsterdam, September 25, 1933). Ehrenfest got full tenure on his Chair at a quite early age, in 1912. Also because of his intellectual generosity, talent and friendship and sense of humor. Leyden became during the Great War and immediately thereafter an excellent place to stay for a longer or shorter while.

The Netherlands stayed neutral during WWI. Ehrenfest’ s foreign visitors and sparring-partners in animated debate and discussion included Albert Einstein and Niels Bohr. In the year that Adolf Hitler came to power in Germany, the jew Paul Ehrenfest took the life of his handicapped son and ended his own life as well. It is seldom that his unimaginable tragedy and drama is mentioned explicitly in chronicles of the development of physics during the 20th century.

In the ‘ Encyclopaedia Britannica’ (ed. 1986) ‘ Ehrenfels, Christian, Freiherr von’ is succeeded by the lemma ‘Ehringsdorf, skull’ describing a human fossil remnant, consisting of a fragmented braincase and lower jaws, found in 1925 near Weimar.

A representative large encyclopaedia in the Dutch language ‘ De Grote Oosthoek’ (ed. 1976) omits any reference to his personal life; and the first biography of one of the most influential scientists of the 20th century was published in 1970. ‘ Normal science’ has always found it hard to deal with existential crises personal.