Paul Langevin

Paul Langevin , born with Paris the January 23rd 1872 and died in Paris the December 19th 1946, is a French, known physicist in particular for its theory of the Magnétisme and the organization of the Congrès Solvay.

Biography

Born just after the Common in a republican family, the young person Paul Langevin is distinguished dice the elementary school as an extraordinarily gifted pupil. He enters at sixteen years to the University of industrial physics and chemistry of the town of Paris (ESPCI) where he follows the courses of Pierre Curie. It is on the councils of the latter that it is directed towards research and teaching rather than towards a career of engineer. In 1894, it is received first with the National university and at the exit of the school, in 1897, a purse enables him to go to work one year with the Cavendish Laboratory of Cambridge, prestigious laboratory hearth of the modern physics directed by J.J. Thomson where it binds friendship with Ernest Rutherford.

It prepares its thesis of doctorate at the Laboratory of teaching of the physics of the Faculty of Science of Paris, directed by Edmond Bouty, and becomes science doctor in 1902.

In 1904, it takes part, with Henri Poincaré, with the international congress of Saint-Louis, where it submits a report/ratio on the physics of the electrons. In 1905, it makes experiments on the ions of the atmosphere since the Eiffel Tower and with the Observatoire of the Peak of the South. It succeeds Pierre Curie at the post of professor of general electricity of the University of industrial physics and chemistry of the town of Paris in 1905 and becomes director of studies of Albin Haller. It succeeds to him the position of director of the University of industrial physics and chemistry of the town of Paris in 1925, station which it will preserve until its death.

He becomes the friend of the Curie, Jean Perrin, physicist, and of Emile Borel. Although it is married, it has a short connection with Marie Curie, then widow, revealed by the press in 1911.

He is prize winner of the Médaille Hughes in 1915. Starting from 1920, it directs the Journal of Physics and Radium .

It is named professor of general and experimental physics to the Collège de France in 1909. Its work on the Magnétisme is worth to him the Médaille Copley in 1940. Because of its opinions antifascists, he is imprisoned on October 30th 1940 by the Gestapo with the Prison of Health. He is released forty days and is assigned later with residence with Troyes, which he leaves clandestinely in May 1944 to join the Suisse. His/her daughter Helene Langevin, married to resistant, Jacques Solomon, is off-set with Auschwitz in 1943 (she will survive it). Jacques Solomon is shot with the Mont Valérien on May 23rd 1942. Paul Langevin adhered in clandestinity to the French Communist party and belonged to the Parisian Committee of the Release. He is released in September 1944 and returns to ensure the direction of ESPCI until his death the December 19th 1946. Its ashes were transferred to the the Pantheon from Paris in 1948.

The scientist

Magnetism

At the time when Paul Langevin starts his scientific career, in 1895, physics is with revolving of its history. The work of Langevin is located the transitional period, of 1900 to 1930, which will be confined of a modern physics having integrated the theory of relativity and the quantum theory. After its thesis, which relates to the ionization of gases, the first work of Paul Langevin concerns the microscopic nature of the Magnétisme. It uses the Physique statistics of Boltzmann to interpret the fact, observed by Pierre Curie, that the Susceptibilité of the paramagnetic materials varies with the temperature. The magnetic materials would be made of a multitude of small magnets created by electrons moving on a closed orbit. The magnetic properties of these materials are then interpreted like the compromise between the tendency of the small magnets to align itself and the thermal agitation which tends to give them a random direction. This theory was published in 1905.

The electron and relativity

In 1906, it prepares a course on the electromagnetic theory for the Collège de France and leads to the result according to which the inertia of the electron would be a property of energy. A few months later, it at the time of reading the publications of Einstein on restricted relativity and seizes the bond between its research and this new revolutionary theory. It is as from this moment that it passes part of its time to spread the new theory. He is the promoter of this theory in France.

He teaches for the first time the theory of the Relativité in his courses with the Collège de France in 1910-1911. He invents the Paradoxe of the twins, whom he introduces for the first time to the Congress of Bologna and the French company of philosophy in 1911.

In 1922, it invites Einstein at the Collège de France to make conferences on relativity. Henri Bergson, which had attended with the congress of Bologna and the conferences of Einstein at the Collège de France, publishes Durée and simultaneity in 1922 and Emile Meyerson the relativistic deduction in 1925.

The equation of Langevin

See also: Equation of Langevin

In 1908, he proposes an equation to describe the random walk of the suspended particles in a liquid, which one generally calls Brownian Movement. This equation corresponds to the writing of the Basic principle of dynamics of an object in a liquid subjected to viscous forces (Force of Stokes) and to a random force corresponding to the ceaseless bombardment of the system by the atoms of the ambient conditions.

The sonar

During the First World War, it develops, with the engineer Constantin Chilowski, the Sonar, apparatus intended to detect the Sous-marin S by using the reflection of the ultrasonic waves on these objects. It is used by the navy of war for the detection of submarines and mines. It is also used for fishing, like in navigation to measure the depth. There can be active or passive sonars.

The popularizer

In 1906, Langevin takes note of the theory of the restricted Relativité of Einstein. Consequently, he becomes a burning proselyte of these novel ideas, in his courses at the Collège de France, or the French company of philosophy. It is him which invites Einstein in France, in 1922, for conference series, in spite of the opposition of the nationalists anti-German. Langevin is the author of the Paradoxe of the twins, Expérience of thought highlighting the effects of the restricted Relativité.

Langevin is at the origin of the Congrès Solvay which join together starting from the 1911 all large physicists of the time. It is also implied, after 1923, in the diffusion of work of its pupil Louis de Broglie by immediately registering the news Wave mechanics with the programme of its course at the Collège de France.

In addition to the Collège de France and the School of physics-chemistry, Langevin also teaches with the section of the electricians of the philotechnic Association (kind of course of the evening), with the National university of Sevres (for young girls), at the working University with Romain Roland and Henri Barbusse.

The militant and the humanistic one

To explain his social and political standpoint, Paul Langevin writes in 1945:

My father who had had, in spite of him, to stop his studies at the eighteen years age, inspired the desire to me to know; he and my mother, eyewitnesses of the seat and the bloody repression of the Commune, have me, by their accounts, put in the middle the horror of violence and the impassioned desire of justice sociale.

It has a militant activity very early: he is signatory as of 1898 of the petition pro-Dreyfus.

Pacifist militant, man of the left and antifascist, it takes part in the Société of the Nations, created after the First World War and positions clearly against the chemical weapons and biological. He is at the origin of the creation of the Comité of vigilance of the intellectuals antifascists.

At the beginning of the German occupation, this notoriety antifascist is worth to him to be stopped on October 30th, 1940. Its arrest is at the origin of the first demonstration anti-allemande, on November 11th, 1940. It is then assigned with residence with Troyes and sign voluntarily at the Teacher training school teachers.

President of the League of the human rights of 1944 with 1946, after of having been the vice-president starting from 1927, it was what one calls a fellow traveller of the French Communist party.

He is also president of the French Groupe of new education of 1936 to 1946, in charge in 1946 of the reform of the teaching which will be known under the name of Plan Langevin-Walloon. He is also president of the rationalist Union of 1938 to 1946.

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