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Paul Ehrenfest, Austrian Physicist
Paul Ehrenfest (January 18, 1880 - September 25, 1933) was an Austrian and Dutch physicist. In 1901 he began course work at Gottingen, which until 1933 was an important center for mathematics and theoretical physics. There he met his future wife Tatyana A. Afanasyeva, a young mathematician. He obtained his degree in 1904. He spent most of his career at Leiden University. His scientific papers dealt with fundamentals, and seek to clarify single points. His publications are renowned for clarity, by solving paradoxes or by providing clearer descriptions, or are inspiring by posing penetrating questions. Ehrenfest's most important contribution from 1912 up to 1933 is the theory of adiabatic invariants. He made major contributions to quantum physics, including the theory of phase transitions and the Ehrenfest theorem, which states that expectation values of a quantum system follow classical mechanics. His name is also given to the Ehrenfest paradox, an apparent paradox in relativity still discussed today. He maintained a close relationship with Niels Bohr and Albert Einstein. It appears that Ehrenfest suffered from severe depression. By August 1932, Einstein was so worried that he wrote to the Board of the University of Leiden, expressing deep concern and suggesting ways in which Ehrenfest's workload could be reduced. In 1933, he lost his battle with depression. Having made arrangements for the care of his other children, he first shot his younger son Wassik, who had Down syndrome, then killed himself. He was 53 years old.
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