| Weinberg, S. (1993). Dreams of a final theory: Search for the ultimate laws of nature. Londres: Hutchinson Radius. |
|
| Last edited by: Dominique Meeùs 2011-05-03 08:46:32 |
Pop. 0%
|
Positivism did harm in other ways that are less well known. There is a famous experiment performed in 1897 by J. J. Thomson, which is generally regarded as the discovery of the electron. […] It turned out that the amount of bending of these rays was consistent with the hypothesis that they are made up of particles that carry a definite quantity of electric charge and a definite quantity of mass. […] For this, Thomson regarded himself, and has become universally regarded by historians, as the discoverer of a new form of matter, a particle […] : the electron.
Yet the same experiment was done in Berlin at just about the same time by Walter Kaufmann. The main difference between Kaufmann’s experiment and Thomson’s was that Kaufmann’s was better. […] Thomson was working in an English tradition going back to Newton, Dalton, and Prout — a tradition of speculation about atoms and their constituents. But Kaufmann was a positivist ; he did not believe that it was the business of physicists to speculate about things that they could not observe. So Kaufmann did not report that he had discovered a new kind of particle, but only that whatever it is that is flowing in a cathode ray, it carries a certain ratio of electric charge to mass.
The moral of this story is not merely that positivism was bad for Kaufmann’s career. Thomson, guided by his belief that he had discovered a fundamental particle, went on and did other experiments to explore its properties. He found evidence of particles with the same ratio of mass to charge emitted in radioactivity and from heated metals, and he carried out an early measurement of the electric charge of the electron. This measurement, together with his earlier measurement of the ratio of charge to mass, provided a value for the mass of the electron. It is the sum of all these experiments that really validates Thomson’s claim to be the discoverer of the electron, but he would probably never have done them if he had not been willing to take seriously the idea of a particle that at that time could not be directly observed. |
| Weinberg, S. (1985). Le monde des particules: De l’électron au quark. Paris: Pour la Science. |
|
| Last edited by: Dominique Meeùs 2011-05-03 08:45:57 |
Pop. 0%
|
| L’une des plus fondamentales raisons qu’avait Thomson d’expliquer ses observations en termes de particules fondamentales était la tradition atomiste qui s’était perpétuée après Leucippe, Démocrite et Dalton. Dans son article de 1897, Thomson cite les hypothèses du chimiste anglais William Prout (1785-1850) qui proposa en 1815 que les quelques douzaines d’atomes connus à l’époque soient constitués d’un seul type fondamental d’atome, l’atome d’hydrogène. Selon Thomson, Prout avait raison, mais l’ « atome » fondamental n’était pas l’atome d’hydrogène : c’était la particule beaucoup plus légère des rayons cathodiques. Aurait-il fait cette hypothèse si Prout et d’autres n’avaient pas auparavant propagé l’idée de particules fondamentales ? Comme nous l’avons vu, à l’époque où Thomson mesurait le rapport masse/charge électrique des particules cathodiques, Walter Kaufmann effectuait à Berlin une expérience comparable avec des résultats plus précis que ceux obtenus par Thomson ; Kaufmann ne prétendit cependant pas avoir découvert une particule fondamentale. Comme Hertz et d’autres physiciens en Allemagne et en Autriche, Kaufmann était fortement influencé par les idées du physicien et philosophe viennois Ernst Mach (1836-1916), qui soutenait, avec son entourage, qu’il n’était pas scientifique de s’intéresser à des objets hypothétiques comme les atomes, que l’on n’observait pas directement. Il est difficile de ne pas conclure que Thomson découvrit les particules que nous appelons aujourd’hui électrons parce que, à la différence de Mach et de Kaufmann, il pensait que la physique consistait aussi à découvrir des particules fondamentales. |
