Famous Scientist Paul Ehrenfest

Paul Ehrenfest

Paul Ehrenfest (January 18, 1880 – September 25, 1933) was an Austrian and Dutch physicist, who made major contributions to the field of statistical mechanics and its relations with quantum mechanics, including the theory of phase transition and the Ehrenfest theorem.


Paul Ehrenfest was born and grew up in Vienna in a Jewish family from Loštice in Moravia. His parents, Sigmund Ehrenfest and Johanna Jellinek, ran a grocery store. Although the family was not overly religious, Paul studied Hebrew and the history of the Jewish people. Later he always emphasized his Jewish roots. Ehrenfest excelled in grade school but did not do well at the Akademisches Gymnasium, his best subject being mathematics. After transferring to the Franz Josef Gymnasium, his marks improved. In 1899 he passed the final exams.

The Ehrenfests returned to Göttingen in September 1906. They would not see Boltzmann again: on September 6 he took his own life in Duino near Trieste. Ehrenfest published an extensive obituary in which Boltzmann’s accomplishments are described. Felix Klein, doyen of the Göttinger mathematicians and chief editor of the Enzyklopädie der mathematischen Wissenschaften, had counted on Boltzmann for a review about statistical mechanics. Now he asked Ehrenfest to take on this task. Together with his wife, Ehrenfest worked on it for several years; the article was not published until 1911. It is a review of the work of Boltzmann and his school, and shows a style all of its own: a sharp logical analysis of the fundamental hypotheses, clear delineation of unsolved questions, and an explanation of general principles by cleverly chosen transparent examples.

In October 1912 Ehrenfest arrived in Leiden, and December 4 he gave his inaugural lecture Zur Krise der Lichtaether-Hypothese (About the crises of the light-ether hypothesis). He remained in Leiden for the rest of his career. In order to stimulate interaction and exchange between physics students he organized a discussion group and a fraternity called De Leidsche Flesch.

He maintained close contact with prominent physicists within the country and abroad, and invited them to visit to Leiden and give a presentation in his lecture series. Ehrenfest was an outstanding debater, quick to point out weaknesses and summarize the essentials.