EHRENFEST, PAUL

EHRENFEST, PAUL (1880–1933), Austrian physicist. Born in Vienna, Ehrenfest studied under Ludwig Boltzmann, the   Austrian physicist, and later went to Goettingen. He and his wife, Tatiana Afanashewa, carried out a critical investigation of kinetic theory, and collaborated in an extensive article on statistical mechanics which is still one of the classics on that subject. From 1912 until his death Ehrenfest was professor of physics at Leiden. His work in that period included papers on the adiabatic hypothesis and invariants (a term he coined), propagation of wave pockets, and ferromagnetic Curie points. Ehrenfest was a masterful teacher, infecting his students with his own enthusiasm for physics. He was a merciless critic of unclear and superficial expositions and in his own work stressed clarity and fundamentals. Ehrenfest became a symbol of a period in physics characterized by two great advances, the quantum theory and the theory of relativity, where fundamental enquiry was the rule. -BIBLIOGRAPHY: H.A. Kramers, in: Nature, 132 (Oct. 28, 1933), 667; G.E. Uhlenbeck et al., in: Science, 78 (Oct. 27, 1933), 377–8. (Gerald E. Tauber)