Paul Ehrenfest

Paul Ehrenfest (Vienna, January 18, 1880 – Amsterdam, September 25, 1933) was an Austrian physicist and mathematician, who obtained Dutch citizenship on March 24, 1922. He made major contributions to the field of statistical mechanics and its relations with quantum mechanics, including the theory of phase transition and the Ehrenfest theorem. On December 21, 1904 he married Russian mathematician Tatyana Alexeyevna Afanasyeva (1876–1964), who collaborated with him in his work. They had two daughters and two sons: Tatyana ('Tanja') (1905–1984), also became a mathematician; Galinka ('Galja') (1910–1979), became an author and illustrator of children's books; Paul Jr. ('Pavlik') (1915–1939), who also became a physicist; and Vassily ('Wassik') (1918–1933). Image File history File links Download high resolution version (930x1266, 104 KB) Title: Paul Ehrenfest Year: unknown Source: http://www. ... Image File history File links Download high resolution version (930x1266, 104 KB) Title: Paul Ehrenfest Year: unknown Source: http://www. ... Vienna (German: Wien [viːn]; Bosnian, Croatian, and Serbian: Beč, Czech: Vídeň, Hungarian: Bécs, Romanian: Viena, Romani: Bech or Vidnya, Russian: Вена, Slovak: Viedeň, Slovenian: Dunaj) is the capital of Austria, and also one of the nine States of Austria. ... January 18 is the 18th day of the year in the Gregorian calendar. ... 1880 (MDCCCLXXX) was a leap year starting on Thursday (see link for calendar). ... Amsterdam Location Flag Country Netherlands Province North Holland Population 742,951(1 January 2005) Coordinates Website www. ... September 25 is the 268th day of the year (269th in leap years). ... 1933 (MCMXXXIII) was a common year starting on Sunday (link will take you to calendar). ... A physicist is a scientist trained in physics. ... Leonhard Euler is considered by many people to be one of the greatest mathematicians of all time A mathematician is a person whose primary area of study and research is mathematics. ... March 24 is the 83rd day of the year in the Gregorian Calendar (84th in Leap years). ... 1922 (MCMXXII) was a common year starting on Sunday (see link for calendar). ... Statistical mechanics is the application of statistics, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... Fig. ... In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ... The Ehrenfest theorem, named after Paul Ehrenfest, relates the time derivative of the expectation value for a quantum mechanical operator to the commutator of that operator with the Hamiltonian of the system. ... December 21 is the 355th day of the year (356th in leap years) in the Gregorian calendar. ... 1904 (MCMIV) was a leap year starting on a Friday (link will take you to calendar). ... Tatyana Afanasyeva Tatyana Alexeyevna Afanasyeva (Kiev, November 19, 1876 – Leiden, April 14, 1964) was a Russian /Dutch mathematician. ... 1876 (MDCCCLXXVI) is a leap year starting on Saturday. ... For the Nintendo 64 emulator, see 1964 (Emulator). ... Tatyana Pavlovna Ehrenfest, later van Aardenne-Ehrenfest, (Vienna, October 28, 1905 – Dordrecht, November 29, 1984) was a Dutch mathematician. ... 1905 (MCMV) was a common year starting on Sunday (see link for calendar). ... 1984 (MCMLXXXIV) was a leap year starting on Sunday of the Gregorian calendar. ... -1... This page refers to the year 1979. ... 1915 (MCMXV) was a common year starting on Friday (see link for calendar). ... 1939 (MCMXXXIX) was a common year starting on Sunday (link will take you to calendar). ... 1918 (MCMXVIII) was a common year starting on Tuesday of the Gregorian calendar (see link for calendar) or a common year starting on Wednesday of the Julian calendar. ... 1933 (MCMXXXIII) was a common year starting on Sunday (link will take you to calendar). ...

Childhood and youth

Paul Ehrenfest grew up in Vienna in a Jewish family that was originally from a village in Moravia. His parents, Sigmund Ehrenfest and Johanna Jellinek, had a thriving grocery store. Although the Ehrenfests were not very religious, Paul nevertheless took courses in Hebrew and the history of the Jewish people. Later he always emphasized his Jewish roots. The word Jew ( Hebrew: יהודי) is used in a wide number of ways, but generally refers to a follower of the Jewish faith, a child of a Jewish mother, or someone of Jewish descent with a connection to Jewish culture or ethnicity and often a combination of these attributes. ... Moravia in relation to the current kraje of the Czech Republic Moravia (Czech and Slovak: Morava, German: ( ), Hungarian: Morvaország, Polish: Morawy) is a historical region in the east of the Czech Republic. ... Hebrew (עִבְרִית ‘Ivrit) is a Semitic language of the Afro-Asiatic language family spoken by more than seven million people in Israel and Jewish communities around the world. ... Jewish history is the history of the Jewish people, faith (Judaism) and culture. ...

Although Ehrenfest excelled in grade school, he did not do well at the Akademisches gymnasium, his best subject being mathematics. However, after he transferred to the Franz Josef gymnasium, things improved and in 1899 he successfully passed the final exams. A gymnasium (pronounced with a hard g) is a type of school of secondary education in parts of Europe. ... Euclid, detail from The School of Athens by Raphael. ... 1899 (MDCCCXCIX) was a common year starting on Sunday (see link for calendar). ... A gymnasium (pronounced with a hard g) is a type of school of secondary education in parts of Europe. ...

Education

He majored in chemistry at the Technische Hochschule, but he also took courses at the University of Vienna, in particular from Ludwig Boltzmann on his kinetic theory of thermodynamics. These lectures had a profound influence: they were instrumental in stimulating Ehrenfest’s interest in theoretical physics, defined his main area of research for years to come, and provided an example of inspired teaching. At the time it was customary in the German-speaking world to study at more than one university and in 1901 Ehrenfest transferred to Göttingen, which until 1933 was an important centre for mathematics and theoretical physics. There he met his future wife Tatyana A. Afanasyeva, a young mathematician born in the Ukraine but educated in Russia. In the spring of 1903 he became acquainted with H.A. Lorentz during a short trip to Leiden. Multicolored chemicals are frequent hallmarks of chemistry. ... Technische Hochschule (acronym TH) is, what a university of technology (i. ... University of Vienna, main building, seen from Beethovens apartment The University of Vienna (German: Universität Wien) in Austria was founded in 1365 by Rudolph IV and hence named Alma mater Rudolphina. ... Ludwig Boltzmann Ludwig Eduard Boltzmann (Vienna, Austria-Hungary, February 20, 1844 – Duino near Trieste, September 5, 1906) is an Austrian physicist famous for his founding contributions in the fields of statistical mechanics and statistical thermodynamics. ... Kinetic theory, or kinetic-molecular theory, or collision theory attempts to explain the macroscopic properties of gases by considering their molecular composition and motion. ... Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... Theoretical physics employs mathematical models and abstractions, as opposed to experimental physics, in an attempt to understand Nature. ... 1901 (MCMI) was a common year starting on Tuesday (see link for calendar) of the Gregorian calendar (or a common year starting on Wednesday of the 13-day-slower Julian calendar). ... Göttingen ( ) is a city in Lower Saxony, Germany. ... 1933 (MCMXXXIII) was a common year starting on Sunday (link will take you to calendar). ... 1903 (MCMIII) was a common year starting on Thursday (see link for calendar). ... Painting of Hendrik Lorentz by Arnhemensis Hendrik Antoon Lorentz (July 18, 1853, Arnhem – February 4, 1928, Haarlem) was a Dutch physicist and the winner of the 1902 Nobel Prize in Physics for his work on electromagnetic radiation. ... Leyden redirects here. ...

In the meantime he prepared a dissertation on a topic in classical mechanics entitled Die Bewegung starrer Körper in Flüssigkeiten und die Mechanik von Hertz (The motion of rigid bodies in fluids and the mechanics of Hertz). He obtained his Ph.D. degree on June 23, 1904 in Vienna, where he stayed from 1904 to 1905. June 23 is the 174th day of the year (175th in leap years) in the Gregorian Calendar, with 191 days remaining. ... 1904 (MCMIV) was a leap year starting on a Friday (link will take you to calendar). ... 1904 (MCMIV) was a leap year starting on a Friday (link will take you to calendar). ... 1905 (MCMV) was a common year starting on Sunday (see link for calendar). ...

Academic career

The Ehrenfests returned to Göttingen in September 1906. They would not see Boltzmann again: on September 6 he took his own life in Duino near Trieste. Ehrenfest published an extensive obituary in which Boltzmann’s accomplishments are described. 1906 (MCMVI) was a common year starting on Monday (see link for calendar). ... This article is about the day of the year. ... Duino castle Duino (Devin in Slovenian, Tybein in German) in the coastal part of the Municipality of Duino-Aurisina, lies in the region of Friuli-Venezia Giulia in the province of Trieste, in north-east Italy. ... Trieste (Latin Tergeste, Italian Trieste, Slovenian, Croatian and Serbian Trst, German and Friulian Triest) is a city and port in northeastern Italy right on the border to Slovenia. ...

Felix Klein, the doyen of the Göttinger mathematicians and chief editor of the Enzyklopädie der mathematischen Wissenschaften, had counted on Boltzmann for a review about statistical mechanics. Now he asked Ehrenfest, known to him from publications and a seminar, to take on this task. Together with his wife, Ehrenfest worked on it for several years; the article was not published until 1911. It is an review of the work of Boltzmann and his school, and shows a style all of its own: a sharp logical analysis of the fundamental hypotheses, clear delineation of unsolved questions, and an explanation of general principles by cleverly chosen transparent examples. Felix Christian Klein (April 25, 1849 – June 22, 1925) was a German mathematician. ... Statistical mechanics is the application of statistics, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... 1911 (MCMXI) was a common year starting on Sunday (click on link for calendar). ...

In 1907 the couple moved to St Petersburg. Ehrenfest found good friends there, in particular A.F. Joffe, and soon felt at home, though scientifically somewhat isolated. Moreover, as an Austrian citizen and of Jewish origin, he had no prospect of a permanent position. Early in 1912 Ehrenfest set out on a tour of German-speaking universities in the hope of a position. He visited Berlin where he saw Max Planck, Leipzig where he saw his old friend Herglotz, Munich where he met Arnold Sommerfeld, then Zurich, Vienna. While in Prague he met Albert Einstein for the first time, and they remained close friends thereafter. Einstein recommended Ehrenfest to succeed him in his position in Prague, but that did not work out because he was without religious affiliation. Sommerfeld offered him a position in Munich, but Ehrenfest received a better offer; at the same time there was an unexpected turn of events. H.A. Lorentz resigned his position as professor at the University of Leiden, and on his advice Ehrenfest was appointed as his successor. 1907 (MCMVII) was a common year starting on Tuesday (see link for calendar) of the Gregorian calendar (or a common year starting on Wednesday of the 13-day-slower Julian calendar). ... Saint Petersburg (Russian: Санкт-Петербу́рг, English transliteration: Sankt-Peterburg), colloquially known as Питер (transliterated Piter), formerly known as Leningrad (Ленингра́д, 1924–1991) and Petrograd (Петрогра́д, 1914–1924), is a city located in Northwestern Russia on the delta of the river Neva at the east end of the Gulf of Finland... Abram Fedorovich Ioffe (Абра́м Фёдорович Ио́ффе, October 29, 1880 (new style) – October 14, 1960) was a prominent Soviet/Russian physicist. ... This article is about the capital city of Germany. ... Max Planck This article is about Planck, the German physicist. ... (help· info) [] (Sorbian/Lusatian: Lipsk) is the largest city in the Federal State (Bundesland) of Saxony in Germany. ... Munich (German: München, (pronounced listen) is the capital of the German Federal State of Bavaria. ... Arnold Johannes Wilhelm Sommerfeld (December 5, 1868 – April 26, 1951) was a German physicist who introduced the fine-structure constant in 1919. ... Location within Switzerland   Zürich[?] (German pronunciation IPA: ; usually spelled Zurich in English) is the largest city in Switzerland (population: 366,145 in 2004; population of urban area: 1,091,732) and capital of the canton of Zürich. ... Prague (Czech: Praha (IPA: ), see also other names) is the capital and largest city of the Czech Republic. ... Albert Einstein, photographed by Yousuf Karsh in 1948. ... Leiden University in the city of Leiden, is the oldest university in the Netherlands. ...

Professor at the University of Leiden

In October 1912 Ehrenfest arrived in Leiden, and December 4 he gave his inaugural lecture Zur Krise der Lichtaether-Hypothese (About the crises of the light-ether hypothesis). He remained in Leiden for the rest of his career. December 4 is the 338th day (339th on leap years) of the Gregorian calendar. ...

Ehrenfest brought about major changes in the tranquil local culture of physics in Leiden. In order to stimulate interaction and exchange between physics students he organized a discussion group and a fraternity, following the example he had encountered in Göttingen. He maintained close contact with nearly all prominent physicists within the country and abroad, and invited many of them over for a visit to Leiden, and to give a presentation for the famous seminar series he organized. Ehrenfest was an outstanding debater, who was quick to point out weaknesses and summarize the essentials. He invited promising young foreign scientists to come for an extended period to Leiden, and his own students were encouraged to spend time abroad. This way he created an international school of theoretical physics, and almost all of his graduate students went on to pursue a successful scientific career of their own.

Ehrenfest's students, Leiden 1924. Left to right: Gerhard Heinrich Dieke, Samuel Abraham Goudsmit, Jan Tinbergen, Paul Ehrenfest, Ralph Kronig, and Enrico Fermi.

Ehrenfest was renowned for his clear teaching. In his lectures he would focus on simple models and examples to illustrate and clarify the underlying assumptions, and tried to avoid mathematical rigor. His classes were small, and the students had a very good interaction with him. He always made an effort to get to know every student who made use of the reading room of his Institute for Theoretical Physics. Though few of them were accepted as majors in Theoretical Physics, he had long discussions with them almost on a daily basis. According to Einstein: "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 emersion in scientific problems". If Ehrenfest felt that there was little more he could teach his students, he would send them to other centers in Europe for more training. He would also encourage them to accept positions abroad. Image File history File links Ehrenfeststudents. ... Image File history File links Ehrenfeststudents. ... Gerhard Heinrich Dieke, (Rheda, Germany, 1901–Aberdeen, Scotland, August 26, 1965 was a German/U.S. physicist. ... Samuel Goudsmit (1902–1978) was a Dutch-American physicist famous for jointly proposing the concept of electron spin with George Eugene Uhlenbeck. ... Jan Tinbergen Jan Tinbergen (The Hague, April 12, 1903 – June 9, 1994 The Hague), Dutch economist, was awarded the first Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel in 1969, which he shared with Ragnar Frisch for having developed and applied dynamic models for the analysis... Ralph Kronig was a a German-American physicist (1904-1995). ... Enrico Fermi in the 1940s Enrico Fermi (September 29, 1901 – November 28, 1954) was an Italian physicist most noted for his work on beta decay, the development of the first nuclear reactor, and for the development of quantum theory. ...

Among his students were Johannes Burgers, Hendrik Kramers, Dirk Coster, George Uhlenbeck and Samuel Goudsmit, who became famous for jointly proposing the concept of electron spin, Jan Tinbergen, Arend Rutgers, Hendrik Casimir, Gerhard Dieke, and Dirk Struik. His assistants included Yuri Krutkov, Viktor Trkal, Adriaan Fokker, Paul Epstein, and Gregory Breit. Other young foreign scientists who spent an extended period in his laboratory included Gunnar Nordström, Enrico Fermi, Igor Tamm, Oskar Klein, Robert Oppenheimer, Walter Elsasser, Ralph Kronig, Werner Heisenberg, and Paul Dirac. Johannes Martinus Burgers (1895-1981) was a Dutch physicist. ... Hendrik Anthony Kramers (Rotterdam, February 2, 1894 – Oegstgeest, April 24, 1952) was a Dutch physicist. ... This article contains information that has not been verified. ... George Eugene Uhlenbeck (December 6, 1900 – October 31, 1988) was a U.S. (Indonesian-born) physicist. ... Samuel Goudsmit (1902–1978) was a Dutch-American physicist famous for jointly proposing the concept of electron spin with George Eugene Uhlenbeck. ... In atomic physics, the spin quantum number is a quantum number that parametrizes the intrinsic angular momentum (or spin angular momentum, or simply spin) of a given particle. ... Jan Tinbergen Jan Tinbergen (The Hague, April 12, 1903 – June 9, 1994 The Hague), Dutch economist, was awarded the first Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel in 1969, which he shared with Ragnar Frisch for having developed and applied dynamic models for the analysis... Arend Joan Rutgers, (Almelo (Netherlands), October 20, 1903 – Almen, September 2, 1998) was a Dutch/Belgian physical chemist. ... Hendrik Brugt Gerhard Casimir (July 15, 1909 – May 4, 2000) was a Dutch physicist. ... Gerhard Heinrich Dieke, (Rheda, Germany, 1901–Aberdeen, Scotland, August 26, 1965 was a German/U.S. physicist. ... Dirk Struik (September 30, 1894-October 21, 2000) was a mathematician and Marxian theoretician in the United States. ... Viktor Trkal (1888-1956]) was an eminent Czech physicist and mathematician who specialized in theoretical quantum physics. ... Adriaan Daniël Fokker (1887–1972) was a Dutch physicist and musician. ... Paul Sophus Epstein (Warsaw, then part of Imperial Russia, now Poland, March 20, 1883–Pasadena, February 8, 1966) is a Russian- American mathematician/physicist. ... Photograph of Gregory Breit. ... Gunnar Nordström (1881-1923) was a Finnish theoretical physicist who is best remembered for his theory of gravitation, which was an early competitor of general relativity. ... Enrico Fermi in the 1940s Enrico Fermi (September 29, 1901 – November 28, 1954) was an Italian physicist most noted for his work on beta decay, the development of the first nuclear reactor, and for the development of quantum theory. ... Igor Yevgenyevich Tamm (Russian И́горь Евге́ньевич Та́мм, also transcribed sometimes as Igor Evgenevich Tamm) (July 8, 1895 – April 12, 1971) was a Soviet/Russian physicist. ... J. Robert Oppie (a. ... Walter Maurice Elsasser (born March 20, 1904, in Mannheim, Germany; died October 14, 1991, in Baltimore) was a physicist and is considered father of the geodynamo theory. ... Ralph Kronig was a a German-American physicist (1904-1995). ... Werner Heisenberg Werner Karl Heisenberg (December 5, 1901 – February 1, 1976) was a celebrated German physicist and Nobel laureate, one of the founders of quantum mechanics. ... Paul Adrien Maurice Dirac Paul Adrien Maurice Dirac, OM (IPA: [dɪræk]) (August 8, 1902 – October 20, 1984) was a British theoretical physicist and a founder of the field of quantum physics. ...

Research

Most of Ehrenfest's scientific papers deal 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. His approach to science is best illustrated to what he wrote to Robert Oppenheimer in the summer of 1928, after Oppenheimer invited himself for an extended stay in Leiden: "If you intend to mount heavy mathematical artillery again during your coming year in Europe, I would ask you not only not to come to Leiden, but if possible not even to Holland, and just because I am really so fond of you and want to keep it that way. But if, on the contrary, you want to spend at least your first few months patiently, comfortably, and joyfully in discussions that keep coming back to the same few points, chatting about a few basic questions with me and our young people- and without thinking much about publishing (!!!)-why then I welcome you with open arms!! ". Characteristically, he did not like the abstraction of the new quantum theory of Heisenberg and Dirac. J. Robert Oppie (a. ...

Ehrenfest’s most important contribution in the period from 1912 up to 1933 is the theory of adiabatic invariants. It is a concept from classical mechanics that on one hand can serve to refine certain methods of the provisional mechanics of the atom – even though initially Ehrenfest did not accept Bohr’s ideas - and on the other hand makes a link between atom mechanics and statistical mechanics. He made major contributions to quantum physics, including the theory of phase transitions and the Ehrenfest theorem. His name is also given to the Ehrenfest paradox, an apparent paradox in relativity still discussed today, and to Ehrenfest Time, the time characterizing the departure of quantum dynamics for observables from classical dynamics. 1912 (MCMXII) was a leap year starting on Monday in the Gregorian calendar (or a leap year starting on Tuesday in the 13-day-slower Julian calendar). ... 1933 (MCMXXXIII) was a common year starting on Sunday (link will take you to calendar). ... An adiabatic invariant in general is a property of motion which is conserved to exponential accuracy in the small parameter representing the typical rate of change of the gross properties of the body. ... Classical mechanics is a branch of physics which studies the deterministic motion of objects. ... The Bohr model of the atom In 1913, Niels Bohr introduced what has become known as the Bohr model of the atom to atomic physics. ... Niels Bohr Niels (Henrik David) Bohr (October 7, 1885 – November 18, 1962) was a Danish physicist who made essential contributions to understanding atomic structure and quantum mechanics. ... Fig. ... In physics, a phase transition is the transformation of a thermodynamic system from one phase to another. ... The Ehrenfest theorem, named after Paul Ehrenfest, relates the time derivative of the expectation value for a quantum mechanical operator to the commutator of that operator with the Hamiltonian of the system. ... The Ehrenfest paradox, first presented by Paul Ehrenfest 1909 in the Physikalische Zeitschrift, is an apparent paradox in relativity. ... Wikisource has original text related to this article: Relativity: The Special and General Theory Albert Einsteins theory of relativity, or simply relativity, refers specifically to two theories: special relativity and general relativity. ...

Ehrenfest was also interested in developing mathematical theories in economics. This interest was stimulated by his notion that there should be an analogy between thermodynamics and economic processes. While this did not result in publications, he did encourage his graduate student Tinbergen to follow up on this. Tinbergen's thesis was devoted to problems both from physics and economics, and he went on to become an economist and was awarded the first Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel in 1969. The Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel (in Swedish Sveriges Riksbanks pris i ekonomisk vetenskap till Alfred Nobels minne), is a prize awarded each year for outstanding intellectual contributions in the field of economics. ...

Albert Einstein and Niels Bohr in Leiden

Niels Bohr and Albert Einstein debating quantum theory at Ehrenfest's home in Leiden (December 1925)

Ehrenfest was particularly close to Einstein and to Bohr. After Niels Bohr's first visit to Leiden in 1919, for Kramers' thesis defense, he wrote to Ehrenfest: "I am sitting and thinking of all what you have told me about so very many different things, and whatever I think of I feel that I have learned so much from you which will be of great importance for me; but, at the same time, I wish so much to express my feeling of happiness over your friendship and of thankfulness for the confidence and sympathy you have shown me, I find myself so utterly incapable of finding words for it". Image File history File links Download high resolution version (1467x2123, 1676 KB) Niels Bohr and Albert Einstein Foto by Paul Ehrenfest (1880-1933) originally uploaded to de. ... Image File history File links Download high resolution version (1467x2123, 1676 KB) Niels Bohr and Albert Einstein Foto by Paul Ehrenfest (1880-1933) originally uploaded to de. ... Niels Bohr Niels (Henrik David) Bohr (October 7, 1885 – November 18, 1962) was a Danish physicist who made essential contributions to understanding atomic structure and quantum mechanics. ... Hendrik Anthony Kramers (Rotterdam, February 2, 1894 – Oegstgeest, April 24, 1952) was a Dutch physicist. ...

On his invitation Einstein accepted in 1920 an appointment as extraordinary professor at the University of Leiden. This arrangement allowed Einstein to visit Leiden for a few weeks every year. At these occasions Einstein would stay at Ehrenfest's home. In 1923 Einstein stayed there for 6 weeks, after German ultra-nationalists in Berlin had made threats against his life. On the occasion of the 50th anniversary of Lorentz' doctorate (December 1925) Ehrenfest invited both Bohr and Einstein over to Leiden, in an attempt to reconcile their scientific differences about the emerging quantum theory. These discussions were continued at the 1927 Solvay Conference, where Ehrenfest much to his dismay had to side with Bohr's position in this great debate. The meaning of the word professor (Latin: one who claims publicly to be an expert) varies. ... Niels Bohr with Albert Einstein at Paul Ehrenfests home in Leiden (December 1925) The Bohr-Einstein debates is a popular name given to what was actually a series of epistemological challenges presented by Albert Einstein against what has come to be called the standard or Copenhagen interpretation of quantum... The portrait of participants to the first Solvay Conference in 1911. ...

Final years

From the correspondence with his close friends of May 1931 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. A mood disorder is a condition whereby the prevailing emotional mood is distorted or inappropriate to the circumstances. ...

On September 25, 1933, he sadly 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's syndrome, then killed himself.

References

• Martin J. Klein, 'Not by Discoveries Alone: the Centennial of Paul Ehrenfest' Physica 106A (1981) 3-14.
• Martin J. Klein, Paul Ehrenfest (Amsterdam, 1970).
• H.A. Kramers, in Physica 13 (1933) 273-276.
• W. Pauli, in Naturwissenschaften 21 (1933) 841-843.
• H.A. Kramers, in Nature 132 (1933) 667.
• idem, 'Physiker als Stilisten', in Naturwissenschaften 23 (1935) 297-301.
• A. Einstein, Out of my later years (New York, [1950]).
• G.E. Uhlenbeck, 'Reminicences of Professor Paul Ehrenfest', in American Journal of Physics 24 (1956) 431-433.
• N. Bohr, 'Discussion With Einstein on Epistemological Problems in Atomic Physics', in 'Albert Einstein: Philosopher-Scientist', P. A. Schilpp, ed., pp. 200-41, The Library of Living Philosophers, Evanston (1949).
• Bolles, Edmund Blair (April 2004). Einstein Defiant: Genius versus Genius in the Quantum Revolution. National Academy Press. ISBN 0309089980.

Edmund Blair Bolles (1942 - ) is an American humanist and author who argues that human freedom, and originality are real and natural, deriving their powers from modifications of animal memory systems. ...

External links

Wikimedia Commons has media related to:

Paul Ehrenfest

• H.B.G. Casimir, Ehrenfest, Paul (1880-1933), in: Biografisch Woordenboek van Nederland (in Dutch).
• Rowdy Boeyink, “In het centrum van het drama” Wetenschappelijke worstelingen van Paul Ehrenfest tussen 1916 – 1925, master's thesis, University Utrecht, 2005 (in Dutch).
• H.B.G. Casimir, Preface to Collected Papers of Paul Ehrenfest
• Frans van Lunteren, Paul Ehrenfest: de Leidse onderzoekschool van een fysicus in diaspora (2003).
• Dieter Hoffmann, Hubert Laitko, and Staffan Müller-Wille, Paul Ehrenfest in: Das Lexikon bedeutender Naturwissenschaftler (in German).
• John J. O'Connor and Edmund F. Robertson. Paul Ehrenfest at the MacTutor History of Mathematics archive.
• S.A. Goudsmit. The discovery of the electron spin.
• Colloquium Ehrenfestii.
• Einstein in Leiden.
• Ph.D. students of P. Ehrenfest: 1918-1931
• Albert Einstein at Ehrenfest's home in Leiden.