Paul Ehrenfest

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Paul Ehrenfest
Albert Einstein visits Paul Ehrenfest in Leiden in 1920. On Einstein's lap the eldest son Paul Ehrenfest (Jr.).

Paul Ehrenfest (born January 18, 1880 in Vienna , † September 25, 1933 in Amsterdam ) was an Austrian physicist .


Ehrenfest grew up as the son of a Jewish merchant in Vienna and studied from 1899 at the local university at the Ludwig Boltzmann . Close study friends at that time were Hans Hahn , Gustav Herglotz and Heinrich Tietze . From 1901 he studied in Göttingen with Felix Klein , David Hilbert , Max Abraham , Ernst Zermelo , Walther Nernst , and Karl Schwarzschild . In 1904 he received his doctorate from Boltzmann in Vienna with a thesis on the movement of rigid bodies in liquids according to Hertz 's mechanics. After that he stayed at the Universities of Vienna and from 1906 in Göttingen, where Felix Klein commissioned him to write the encyclopedia article on statistical mechanics . He worked on it for the following years with his wife Tatjana Ehrenfest-Afanassjewa , first in Göttingen and from 1907 to 1912 in Saint Petersburg . He did not have a permanent position, but was in contact with the St. Petersburg mathematicians (such as Alexander Friedmann , Tamarkin , Steklow ) and made another degree in physics. In 1911/12 he traveled through Western Europe in search of a job, where he first met Albert Einstein in Prague . From 1912 he was professor for theoretical physics at the University of Leiden , as the successor of the leading theoretical physicist Hendrik Antoon Lorentz at the time . Arnold Sommerfeld recommended him , who was impressed by Ehrenfest's lectures.

Since 1904 he was married to the Russian mathematician Tatjana Ehrenfest-Afanassjewa , who had studied with him in Göttingen and with whom he had two daughters ( Tatjana van Aardenne-Ehrenfest , Galinka) and two sons (Paul Jr., Vassily). Ehrenfest, who suffered from depression , shot himself on September 25, 1933. He intended to commit suicide in a letter to his friends and colleagues Niels Bohr , Albert Einstein , James Franck , Gustav Herglotz , Abram Fjodorowitsch Ioffe , Philip Kohnstamm and Richard C. Tolman to announce, but this letter was not sent. In it he expresses himself skeptical about his ability to continue working in physics, the development of which, according to his own words, he can no longer follow. He also suffered badly from the disability ( Down's syndrome ) of his son Vassily, whom he shot before he committed suicide.


His contribution to modern physics is above all his famous article on statistical mechanics in the Encyclopedia of Mathematical Sciences (with his urn model to explain irreversible phenomena, the quasi-ergodic hypothesis, etc.) from 1911 and the Ehrenfest theorem (1927) named after him Theorem of quantum mechanics , which establishes a generally valid relationship to classical physics . In 1911 he published his adiabatic hypothesis (Annalen der Physik).

The Ehrenfest paradox that he established in 1909 is still often discussed today , an apparent paradox of the special theory of relativity (SRT). This “paradox” was very useful for the later development of the concept of the “rigid body” in the context of special relativity, with publications for exact solutions on this topic appearing to this day. The questions raised were also extremely fruitful for the development of Albert Einstein's general theory of relativity , as it made Einstein aware of the importance of non-Euclidean geometry . Ehrenfest himself became an important defender of the special theory of relativity from 1910 and published several papers in which he went into the misinterpretations of the special theory of relativity by other authors such as Vladimir Sergeyevich Ignatovsky . Around this time Ehrenfest became a friend of Einstein, with whom he was in correspondence. Along with Hendrik Antoon Lorentz , Ehrenfest was also one of the few who supported Einstein in his efforts on general relativity.

He also corresponded with Niels Bohr . In 1925, at a meeting with him in Leiden, he tried to bring about an agreement between Einstein and Bohr in quantum theory, but was unsuccessful.

The Ehrenfest classification of phase transitions is named after him.

His students included Samuel Goudsmit , George Uhlenbeck , Jan Tinbergen and Hendrik Casimir .

On June 18, 2008 the asteroid (32796) Ehrenfest was named after him.


Wikisource: Paul Ehrenfest  - Sources and full texts
  • Paul and Tatjana Ehrenfest: Conceptual foundations of the statistical conception in mechanics. In: Encyclopedia of Mathematical Sciences . 1909, 1911 ( online ).
  • Paul Ehrenfest: Which features of the light quantum hypothesis play an essential role in the theory of thermal radiation? In: Annals of Physics. Series 4, Volume 36, No. 11, 1911, pp. 91-118, doi : 10.1002 / andp.19113411106 .


Web links

Commons : Paul Ehrenfest  - Album with pictures, videos and audio files