Ehrenfest, Paul(poul ā`rənfĕst), 1880–1933, Austrian physicist. In 1904, Ehrenfest received his doctorate in theoretical physics in Vienna and married the Russian mathematician Tatyana Alexeyevna Afanassyewa. Together they wrote what has become a classical exposition of statistical mechanics. He was one of the first to take German physicist Max Planck's quantum theory seriously and to try to define its relation to the older physics. In 1912 he succeeded Dutch physicist H. A. Lorentz in the chair of theoretical physics at the Univ. of Leiden. He proved an energetic, lucid, and inspiring teacher. His acute criticisms and his formulation of the adiabatic principle—which Niels Bohr placed among the foundations of quantum theory—were important contributions to advancing modern physics.
See M. J. Klein, Paul Ehrenfest: The Making of a Theoretical Physicist (Vol. 1, 2d ed. 1985).
Born Jan. 18, 1880, in Vienna; died Sept. 25, 1933, in Amsterdam. Dutch theoretical physicist. Student of L. Boltzmann.
Ehrenfest graduated from the University of Vienna in 1904; he then moved with his wife, the Russian physicist T. A. Afanas’eva-Ehrenfest, to Russia. Beginning in 1912, he was a professor at the University of Leiden (the Netherlands). His principal works dealt with the substantiation of statistical mechanics, quantum theory, relativity theory, and the theory of phase transitions. Ehrenfest developed (1916) the method of adiabatic invariants in quantum theory. He formulated (1927) the theorem of the average values of quantum-mechanical quantities (Ehrenfest theorem). He also derived (1933) the Ehrenfest relations. Ehrenfest exerted a considerable influence on the development of theoretical physics in Russia and the Soviet Union. He was a foreign member of the Academy of Sciences of the USSR (1924).
WORKSCollected Scientific Papers. Amsterdam, 1959.
In Russian translation:
Otnositel’nost’; Kvanty; Statistika. Moscow, 1972.
REFERENCESFrenkel’, V. Ia. Paul’ Erenfest. Moscow, 1977.
Klein, M. J. Paul Ehrenfest, vol. 1. Amsterdam–London, 1970.