Paul Ehrenfest
Encyclopedia
Paul Ehrenfest was an Austria
n and Dutch
physicist
, who 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
.
in a Jewish family from Loštice
in Moravia
. His parents, Sigmund Ehrenfest and Johanna Jellinek, ran a grocery store. Although the family was not overly religious, Paul studied Hebrew
and the history of the Jewish people
. Later he always emphasized his Jewish roots. Ehrenfest excelled in grade school but did not do well at the Akademisches Gymnasium, his best subject being mathematics
. After transferring to the Franz Josef Gymnasium, his marks improved. In 1899 he successfully passed the final exams.
He majored in chemistry
at the Technische Hochschule
, but 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 Ukraine
and educated in Russia
. In the spring of 1903 he met H.A. Lorentz
during a short trip to Leiden. In the meantime he prepared a dissertation on 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.
On December 21, 1904 he married Russia
n 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).
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. Felix Klein
, 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 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 a 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.
In 1907 the couple moved to St Petersburg. Ehrenfest found good friends there, in particular A.F. Joffe, but felt scientifically 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
and 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. 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.
In his lectures he would focus on simple models and examples to illustrate and clarify the underlying assumptions. His classes were small, and he made an effort to get to know students who made use of the reading room. 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 immersion 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.
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
, Dirk Struik
, and Gerard Kuiper
. 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
, Paul Dirac
, and David Dennison
.
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.
Ehrenfest’s most important contribution from 1912 up to 1933 is the theory of adiabatic invariant
s. It is a concept derived from classical mechanics
that on the one hand can serve to refine certain methods of Bohr's model of the atom
(although initially Ehrenfest did not accept Bohr
’s ideas) and on the other hand makes a link between atomic mechanics and statistical mechanics. 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, to the Ehrenfest model
, and to Ehrenfest Time, the time characterizing the departure of quantum dynamics for observables from classical dynamics.
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.
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".
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.
. 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 Amsterdam
, on September 25, 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.
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
n and Dutch
Dutch people
The Dutch people are an ethnic group native to the Netherlands. They share a common culture and speak the Dutch language. Dutch people and their descendants are found in migrant communities worldwide, notably in Suriname, Chile, Brazil, Canada, Australia, South Africa, New Zealand, and the United...
physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
, who made major contributions to the field of statistical mechanics
Statistical mechanics
Statistical mechanics or statistical thermodynamicsThe terms statistical mechanics and statistical thermodynamics are used interchangeably...
and its relations with quantum mechanics, including the theory of phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....
and the Ehrenfest theorem
Ehrenfest theorem
The Ehrenfest theorem, named after Paul Ehrenfest, the Austrian physicist and mathematician, 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...
.
Biography
Paul Ehrenfest was born and grew up in ViennaVienna
Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...
in a Jewish family from Loštice
Loštice
Loštice is a town in the Olomouc Region of the Czech Republic. It has around 3,100 inhabitants.Village Žádlovice is an administrative part of Loštice.Loštice's well known product is traditional cheese, called tvarůžek or syreček-External links:...
in Moravia
Moravia
Moravia is a historical region in Central Europe in the east of the Czech Republic, and one of the former Czech lands, together with Bohemia and Silesia. It takes its name from the Morava River which rises in the northwest of the region...
. His parents, Sigmund Ehrenfest and Johanna Jellinek, ran a grocery store. Although the family was not overly religious, Paul studied Hebrew
Hebrew language
Hebrew is a Semitic language of the Afroasiatic language family. Culturally, is it considered by Jews and other religious groups as the language of the Jewish people, though other Jewish languages had originated among diaspora Jews, and the Hebrew language is also used by non-Jewish groups, such...
and the history of the Jewish people
Jewish history
Jewish history is the history of the Jews, their religion and culture, as it developed and interacted with other peoples, religions and cultures. Since Jewish history is over 4000 years long and includes hundreds of different populations, any treatment can only be provided in broad strokes...
. Later he always emphasized his Jewish roots. Ehrenfest excelled in grade school but did not do well at the Akademisches Gymnasium, his best subject being mathematics
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
. After transferring to the Franz Josef Gymnasium, his marks improved. In 1899 he successfully passed the final exams.
He majored in chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
at the Technische Hochschule
Technische Hochschule
Technische Hochschule is what an Institute of Technology used to be called in German-speaking countries, as well as in the Netherlands, before most of them changed their name to Technische Universität or Technische Universiteit in the 1970s and in the...
, but took courses at the University of Vienna
University of Vienna
The University of Vienna is a public university located in Vienna, Austria. It was founded by Duke Rudolph IV in 1365 and is the oldest university in the German-speaking world...
, in particular from Ludwig Boltzmann
Ludwig Boltzmann
Ludwig Eduard Boltzmann was an Austrian physicist famous for his founding contributions in the fields of statistical mechanics and statistical thermodynamics...
on his kinetic theory
Kinetic theory
The kinetic theory of gases describes a gas as a large number of small particles , all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container...
of thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
. These lectures had a profound influence: they were instrumental in stimulating Ehrenfest’s interest in theoretical physics
Theoretical physics
Theoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...
, 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
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....
-speaking world to study at more than one university and in 1901 Ehrenfest transferred to Göttingen
Göttingen
Göttingen is a university town in Lower Saxony, Germany. It is the capital of the district of Göttingen. The Leine river runs through the town. In 2006 the population was 129,686.-General information:...
, 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 Ukraine
Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...
and educated in Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. In the spring of 1903 he met H.A. Lorentz
Hendrik Lorentz
Hendrik Antoon Lorentz was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for the discovery and theoretical explanation of the Zeeman effect...
during a short trip to Leiden. In the meantime he prepared a dissertation on 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.
On December 21, 1904 he married Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n mathematician Tatyana Alexeyevna Afanasyeva (1876–1964), who collaborated with him in his work. They had two daughters and two sons: Tatyana ('Tanja')
Tatyana Pavlovna Ehrenfest
Tatyana Pavlovna Ehrenfest, later van Aardenne-Ehrenfest, was a Dutch mathematician. She was the daughter of Paul Ehrenfest and Tatyana Alexeyevna Afanasyeva .Tatyana Ehrenfest was born in Vienna, and spent her childhood in St Petersburg...
(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).
The Ehrenfests returned to Göttingen in September 1906. They would not see Boltzmann again: on September 6 he took his own life in Duino
Duino
Duino is a town at the Adriatic coast in the municipality of Duino-Aurisina, part of the region of Friuli – Venezia Giulia in the province of Trieste, north-eastern Italy....
near Trieste
Trieste
Trieste is a city and seaport in northeastern Italy. It is situated towards the end of a narrow strip of land lying between the Adriatic Sea and Italy's border with Slovenia, which lies almost immediately south and east of the city...
. Ehrenfest published an extensive obituary in which Boltzmann’s accomplishments are described. Felix Klein
Felix Klein
Christian Felix Klein was a German mathematician, known for his work in group theory, function theory, non-Euclidean geometry, and on the connections between geometry and group theory...
, doyen of the Göttinger mathematicians and chief editor of the Enzyklopädie der mathematischen Wissenschaften, had counted on Boltzmann for a review about statistical mechanics
Statistical mechanics
Statistical mechanics or statistical thermodynamicsThe terms statistical mechanics and statistical thermodynamics are used interchangeably...
. Now he asked Ehrenfest 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 a 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.
In 1907 the couple moved to St Petersburg. Ehrenfest found good friends there, in particular A.F. Joffe, but felt scientifically 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
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....
-speaking universities in the hope of a position. He visited Berlin
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...
where he saw Max Planck
Max Planck
Max Karl Ernst Ludwig Planck, ForMemRS, was a German physicist who actualized the quantum physics, initiating a revolution in natural science and philosophy. He is regarded as the founder of the quantum theory, for which he received the Nobel Prize in Physics in 1918.-Life and career:Planck came...
, Leipzig
Leipzig
Leipzig Leipzig has always been a trade city, situated during the time of the Holy Roman Empire at the intersection of the Via Regia and Via Imperii, two important trade routes. At one time, Leipzig was one of the major European centres of learning and culture in fields such as music and publishing...
where he saw his old friend Herglotz, Munich
Munich
Munich The city's motto is "" . Before 2006, it was "Weltstadt mit Herz" . Its native name, , is derived from the Old High German Munichen, meaning "by the monks' place". The city's name derives from the monks of the Benedictine order who founded the city; hence the monk depicted on the city's coat...
where he met Arnold Sommerfeld
Arnold Sommerfeld
Arnold Johannes Wilhelm Sommerfeld was a German theoretical physicist who pioneered developments in atomic and quantum physics, and also educated and groomed a large number of students for the new era of theoretical physics...
, then Zurich
Zürich
Zurich is the largest city in Switzerland and the capital of the canton of Zurich. It is located in central Switzerland at the northwestern tip of Lake Zurich...
and Vienna. While in Prague
Prague
Prague is the capital and largest city of the Czech Republic. Situated in the north-west of the country on the Vltava river, the city is home to about 1.3 million people, while its metropolitan area is estimated to have a population of over 2.3 million...
he met Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
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. 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
Leiden University
Leiden University , located in the city of Leiden, is the oldest university in the Netherlands. The university was founded in 1575 by William, Prince of Orange, leader of the Dutch Revolt in the Eighty Years' War. The royal Dutch House of Orange-Nassau and Leiden University still have a close...
, and on his advice Ehrenfest was appointed as his successor.
Academic career
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. In order to stimulate interaction and exchange between physics students he organized a discussion group and a fraternity called De Leidsche Flesch. He maintained close contact with prominent physicists within the country and abroad, and invited them to visit to Leiden and give a presentation in his lecture series. Ehrenfest was an outstanding debater, quick to point out weaknesses and summarize the essentials.In his lectures he would focus on simple models and examples to illustrate and clarify the underlying assumptions. His classes were small, and he made an effort to get to know students who made use of the reading room. 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 immersion 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.
Among his students were Johannes Burgers
Johannes Martinus Burgers
-External links:* A.J.Q. Alkemade, , in Biografisch Woordenboek van Nederland. * , biography at the University of Maryland* * at the University of Maryland*...
, Hendrik Kramers
Hendrik Anthony Kramers
Hendrik Anthony "Hans" Kramers was a Dutch physicist.-Background and education:...
, Dirk Coster
Dirk Coster
Dirk Coster , was a Dutch physicist. He was a Professor of Physics and Meteorology at the University of Groningen....
, George Uhlenbeck
George Eugene Uhlenbeck
George Eugene Uhlenbeck was a Dutch-American theoretical physicist.-Background and education:George Uhlenbeck was the son of Eugenius and Anne Beeger Uhlenbeck...
and Samuel Goudsmit
Samuel Abraham Goudsmit
Samuel Abraham Goudsmit was a Dutch-American physicist famous for jointly proposing the concept of electron spin with George Eugene Uhlenbeck in 1925.-Biography:...
, who became famous for jointly proposing the concept of electron spin
Spin quantum number
In atomic physics, the spin quantum number is a quantum number that parameterizes the intrinsic angular momentum of a given particle...
, Jan Tinbergen
Jan Tinbergen
Jan Tinbergen , was a Dutch economist. He 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 of economic processes...
, Arend Rutgers
Arend Joan Rutgers
Arend Joan Rutgers was a Dutch/Belgian physical chemist.Arend Joan Rutgers went to high school in Almelo, after which he studied chemistry at the University of Amsterdam. After he obtained his master's degree in 1926 he went to Leiden, where he studied theoretical physics under Paul Ehrenfest...
, Hendrik Casimir
Hendrik Casimir
Hendrik Brugt Gerhard Casimir FRS was a Dutch physicist best known for his research on the two-fluid model of superconductors in 1934 and the Casimir effect Hendrik Brugt Gerhard Casimir FRS (July 15, 1909 in The Hague, Netherlands – May 4, 2000 in Heeze) was a Dutch physicist best known...
, Gerhard Dieke
Gerhard Heinrich Dieke
Gerhard Heinrich Dieke, Gerhard Heinrich Dieke, Gerhard Heinrich Dieke, (Rheda, Germany, 1901–Aberdeen, Scotland, August 26, 1965 was a German/U.S. physicist. He was a pioneer in investigating the structure of atoms and molecules by spectroscopic methods....
, Dirk Struik
Dirk Jan Struik
Dirk Jan Struik was a Dutch mathematician and Marxian theoretician who spent most of his life in the United States.- Life :...
, and Gerard Kuiper
Gerard Kuiper
Gerard Peter Kuiper , Netherlands – December 24, 1973, Mexico City) was a Dutch-American astronomer after whom the Kuiper belt was named.-Early life:...
. His assistants included Yuri Krutkov, Viktor Trkal
Viktor Trkal
Viktor Trkal was an eminent Czech physicist and mathematician who specialized in theoretical quantum physics...
, Adriaan Fokker
Adriaan Fokker
Adriaan Daniël Fokker , was a Dutch physicist and musician.Fokker was born in Buitenzorg, Dutch East Indies ; he was a cousin of the aeronautical engineer Anthony Fokker...
, Paul Epstein
Paul Sophus Epstein
Paul Sophus Epstein was a Russian-American mathematical physicist...
, and Gregory Breit
Gregory Breit
Gregory Breit was a Russian-born American physicist and professor at universities in New York, Wisconsin, Yale, and Buffalo...
. Other young foreign scientists who spent an extended period in his laboratory included Gunnar Nordström
Gunnar Nordström
Gunnar Nordström was a Finnish theoretical physicist best remembered for his theory of gravitation, which was an early competitor of general relativity...
, Enrico Fermi
Enrico Fermi
Enrico Fermi was an Italian-born, naturalized American physicist particularly known for his work on the development of the first nuclear reactor, Chicago Pile-1, and for his contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics...
, Igor Tamm
Igor Tamm
Igor Yevgenyevich Tamm was a Soviet physicist and Nobel laureate who received most prestigious Nobel Prize in Physics, jointly with Pavel Alekseyevich Cherenkov and Ilya Frank, for the discovery of Cherenkov radiation, made in 1934.-Biography:Tamm was born in Vladivostok, Russian Empire , in a...
, Oskar Klein
Oskar Klein
Oskar Benjamin Klein was a Swedish theoretical physicist.Klein was born in Danderyd outside Stockholm, son of the chief rabbi of Stockholm, Dr. Gottlieb Klein from Homonna in Hungary and Antonie Levy...
, Robert Oppenheimer
Robert Oppenheimer
Julius Robert Oppenheimer was an American theoretical physicist and professor of physics at the University of California, Berkeley. Along with Enrico Fermi, he is often called the "father of the atomic bomb" for his role in the Manhattan Project, the World War II project that developed the first...
, Walter Elsasser
Walter M. Elsasser
Walter Maurice Elsasser was a German-born American physicist considered a "father" of the presently accepted dynamo theory as an explanation of the Earth's magnetism. He proposed that this magnetic field resulted from electric currents induced in the fluid outer core of the Earth...
, Ralph Kronig
Ralph Kronig
Ralph Kronig was a German-American physicist . He is noted for the discovery of particle spin and for his theory of x-ray absorption spectroscopy...
, Werner Heisenberg
Werner Heisenberg
Werner Karl Heisenberg was a German theoretical physicist who made foundational contributions to quantum mechanics and is best known for asserting the uncertainty principle of quantum theory...
, Paul Dirac
Paul Dirac
Paul Adrien Maurice Dirac, OM, FRS was an English theoretical physicist who made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics...
, and David Dennison
David M. Dennison
David Mathias Dennison was an American physicist who made contributions to quantum mechanics, spectroscopy, and the physics of molecular structure.-Education:...
.
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 by what he wrote to Robert OppenheimerRobert Oppenheimer
Julius Robert Oppenheimer was an American theoretical physicist and professor of physics at the University of California, Berkeley. Along with Enrico Fermi, he is often called the "father of the atomic bomb" for his role in the Manhattan Project, the World War II project that developed the first...
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.
Ehrenfest’s most important contribution from 1912 up to 1933 is the theory of adiabatic invariant
Adiabatic invariant
An adiabatic invariant is a property of a physical system that stays constant when changes occur slowly.In thermodynamics, an adiabatic process is a change that occurs without heat flow, and slowly compared to the time to reach equilibrium. In an adiabatic process, the system is in equilibrium at...
s. It is a concept derived from classical mechanics
Classical mechanics
In physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces...
that on the one hand can serve to refine certain methods of Bohr's model of the atom
Bohr model
In atomic physics, the Bohr model, introduced by Niels Bohr in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction,...
(although initially Ehrenfest did not accept Bohr
Niels Bohr
Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in...
’s ideas) and on the other hand makes a link between atomic mechanics and statistical mechanics. He made major contributions to quantum physics, including the theory of phase transitions and the Ehrenfest theorem
Ehrenfest theorem
The Ehrenfest theorem, named after Paul Ehrenfest, the Austrian physicist and mathematician, 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...
, which states that expectation values
Expectation value (quantum mechanics)
In quantum mechanics, the expectation value is the predicted mean value of the result of an experiment. Despite the name, it is not the most probable value of a measurement...
of a quantum system follow classical mechanics. His name is also given to the Ehrenfest paradox
Ehrenfest paradox
The Ehrenfest paradox concerns the rotation of a "rigid" disc in the theory of relativity.In its original formulation as presented by Paul Ehrenfest 1909 in the Physikalische Zeitschrift, it discusses an ideally rigid cylinder that is made to rotate about its axis of symmetry...
, an apparent paradox in relativity
Theory of relativity
The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance....
still discussed today, to the Ehrenfest model
Ehrenfest model
The Ehrenfest model of diffusion was proposed by Paul Ehrenfest to explain the second law of thermodynamics. The model considers N particles in two containers. Particles independently change container at a rate λ...
, and to Ehrenfest Time, the time characterizing the departure of quantum dynamics for observables from classical dynamics.
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.
Einstein and Bohr in Leiden
Niels Bohr
Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in...
. After Niels Bohr's first visit to Leiden in 1919, for Kramers'
Hendrik Anthony Kramers
Hendrik Anthony "Hans" Kramers was a Dutch physicist.-Background and education:...
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".
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
Solvay Conference
The International Solvay Institutes for Physics and Chemistry, located in Brussels, were founded by the Belgian industrialist Ernest Solvay in 1912, following the historic invitation-only 1911 Conseil Solvay, the turning point in world physics...
, where Ehrenfest much to his dismay had to side with Bohr's position in this great debate.
Final years
From the correspondence with his close friends of May 1931 it appears that Ehrenfest suffered from severe depressionMood disorder
Mood disorder is the term designating a group of diagnoses in the Diagnostic and Statistical Manual of Mental Disorders classification system where a disturbance in the person's mood is hypothesized to be the main underlying feature...
. 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 Amsterdam
Amsterdam
Amsterdam is the largest city and the capital of the Netherlands. The current position of Amsterdam as capital city of the Kingdom of the Netherlands is governed by the constitution of August 24, 1815 and its successors. Amsterdam has a population of 783,364 within city limits, an urban population...
, on September 25, 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
Down syndrome
Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th...
, then killed himself.
External links
- H.B.G. Casimir, Ehrenfest, Paul (1880-1933), in: Biografisch Woordenboek van Nederland (in Dutch).
- Marijn Hollestelle, 'Zuivere praktijk: Paul Ehrenfests opvattingen over toegepaste natuurkunde', in: L. J. Dorsman en P. J. Knegtmans, 'Onderzoek in opdracht: de publieke functie van de universitaire wetenschap in Nederland sedert 1876', (2007).
- Marijn Hollestelle, Paul Ehrenfest. Worstelingen met de moderne wetenschap, 1912-1933 (Leiden University Press, Leiden, 2011) Biography on Ehrenfests life in Leiden. ISBN: 9789087281229
- Rowdy Boeyink, “In het centrum van het drama” Wetenschappelijke worstelingen van Paul Ehrenfest tussen 1916 – 1925, master's thesis, University Utrecht, 2005 (in Dutch).
- Dirk van Delft, Einstein in Leiden, Physics Today 59 (April 2006) 57-26. The frontpage shows a painting by Marijke Kamerlingh Onnes, niece of HeikeHeike Kamerlingh OnnesHeike Kamerlingh Onnes was a Dutch physicist and Nobel laureate. He pioneered refrigeration techniques, and he explored how materials behaved when cooled to nearly absolute zero. He was the first to liquify helium...
. - 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).
- 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.