Editing Paul Ehrenfest (section)

=== Academic career ===
In October 1912, Ehrenfest arrived in Leiden, and on 4 December, he gave his inaugural lecture, ''Zur Krise der Lichtaether-Hypothese'' (About the crisis of the light-ether hypothesis). He remained in Leiden for the rest of his career. To stimulate interaction and exchange among physics students, Ehrenfest organized a discussion group and a study association called ''De Leidsche Flesch'' ("The [[Leyden jar]]"). He maintained close contact with prominent physicists in the country and abroad, and invited them to visit Leiden and give presentations in his lecture series.<ref>{{cite web | url=http://www.lorentz.leidenuniv.nl/history/colloquium/colloquium.html | title = Colloquium Ehrenfestii | publisher = Leiden University |date = n.d. | access-date = 27 February 2020}}</ref> Ehrenfest was an outstanding debater, quick to point out weaknesses and summarize the essentials. 
[[File:Ehrenfeststudents.jpg|thumb|Ehrenfest's students, Leiden 1924. Left to right: [[Gerhard Heinrich Dieke]], [[Samuel Abraham Goudsmit]], [[Jan Tinbergen]], Paul Ehrenfest, [[Ralph Kronig]], and [[Enrico Fermi]]]] 
 
In his lectures, Ehrenfest emphasized simple models and examples to illustrate and clarify basic assumptions. His classes were small, and he made an effort to get to know students who made use of the reading room.<ref>{{cite web|url=http://www.lorentz.leidenuniv.nl/ | title = Lorentz Institute for Theoretical Physics | publisher = Leiden University |date = n.d. | access-date = 27 February 2020}}</ref> Though few of them were accepted as majors in theoretical physics, he had long discussions with them almost daily. According to Einstein:

<blockquote>
He was not merely the best teacher in our profession whom I have ever known; he was also passionately preoccupied with the development and destiny of men, especially his students. To understand others, to gain their friendship and trust, to aid anyone embroiled in outer or inner struggles, to encourage youthful talent—all this was his real element, almost more than his immersion in scientific problems.<ref name=rowdy>{{cite book | last = Einstein | first = Albert | title = Out of My Later Years | publisher = Greenwood Press | location = Westport, Conn | year = 1970 | orig-year = 1956 | chapter = Paul Ehrenfest in Memoriam | page = 236| isbn = 9780837120867 }} Quoted in {{cite web | last = Boeyink | first = Rowdy | title = Ehrenfest and the New Physics in the Interbellum Work and life of Paul Ehrenfest Between 1916 and 1925 | url = http://www.lorentz.leidenuniv.nl/history/Einstein_archive/Rowdy_Boeyink_website/ | url-status = dead | archive-url = https://web.archive.org/web/20140312224422/http://www.lorentz.leidenuniv.nl/history/Einstein_archive/Rowdy_Boeyink_website/ | archive-date = 12 March 2014 | access-date = 27 February 2020}}</ref>
</blockquote>

If Ehrenfest felt there was little more he could teach a student, he would send them to other centers in Europe for more training. He would also encourage students to accept positions abroad. Among his students were [[Johannes Martinus Burgers|Johannes Burgers]], [[Hendrik Anthony Kramers|Hendrik Kramers]], [[Dirk Coster]], [[George Eugene Uhlenbeck|George Uhlenbeck]] and [[Samuel Abraham Goudsmit|Samuel Goudsmit]], who became famous for jointly proposing the concept of [[Spin quantum number|electron spin]], [[Jan Tinbergen]], [[Arend Joan Rutgers|Arend Rutgers]], [[Hendrik Casimir]], [[Gerhard Heinrich Dieke|Gerhard Dieke]], [[Dirk Jan Struik|Dirk Struik]], and [[Gerard Kuiper]]. His assistants included [[Yuri Krutkov]], [[Viktor Trkal]], [[Adriaan Fokker]], [[Paul Sophus Epstein|Paul Epstein]], and [[Gregory Breit]]. Other young foreign scientists who spent extended periods in his laboratory included [[Gunnar Nordström]], [[Enrico Fermi]], [[Igor Tamm]], [[Oskar Klein]], [[J. Robert Oppenheimer]], [[Walter M. Elsasser|Walter Elsasser]], [[Ralph Kronig]], [[Werner Heisenberg]], [[Paul Dirac]], and [[David M. Dennison|David Dennison]].

Ehrenfest had ambivalent opinions about science, technological progress, and cultural and social issues.<ref name="isis201309">{{Cite journal | doi = 10.1086/673271| pmid = 24341262| title = Paul Ehrenfest and the Dilemmas of Modernity | journal = Isis| volume = 104| issue = 3| pages = 504–36| date = September 2013| last1 = Van Lunteren | first1 = F. H. | last2 = Hollestelle | first2 = M. J. | s2cid = 24103865}}</ref>

In 1919, he became a member of the [[Royal Netherlands Academy of Arts and Sciences]].<ref>{{cite web |url=http://www.dwc.knaw.nl/biografie/pmknaw/?pagetype=authorDetail&aId=PE00000099 | title = Paul Ehrenfest (1880–1933) | author = Royal Netherlands Academy of Arts and Sciences | work = KNAW Past Members | date = n.d. | access-date = 27 February 2020}}</ref>