Walter Kaufmann (physicist)

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Walter Kaufmann
Walter kaufmann.png
Born June 5, 1871
Died January 1, 1947
Freiburg im Breisgau
Citizenship German
Known for Proof of the velocity dependence of mass

Walter Kaufmann (June 5, 1871 – January 1, 1947) was a German physicist. He is most well known for his first experimental proof of the velocity dependence of mass, which was an important contribution to the development of modern physics, including special relativity.


In 1890/91 he studied mechanical engineering at the technical universities of Berlin and Munich, since 1892 he studied physics at the Universities of Berlin and Munich and in 1894 he attained a doctorate. Starting from 1896 he worked as an assistant at the physical institutes of the Universities of Berlin and Göttingen. Kaufmann habilitated in 1899 and became a professor extraordinarius of physics in at the University of Bonn. After a renewed activity at the Berliner Physikalisches Institut he followed a call as professor ordinarius for experimental physics and leader of the physical institute at the Albertina in Königsberg, where he taught up to his retirement in 1935. Subsequently, he worked as a guest lecturer at the University of Freiburg.[1]

Measurements of velocity dependence of mass[edit]

His early work (1901–1903) confirmed for the first time the velocity dependence of the electromagnetic mass of the electron (later called relativistic mass). However, those measurements were not precise enough to differentiate between the Lorentz ether theory of Hendrik Antoon Lorentz and the theory of Max Abraham.

At the end of 1905 he performed experiments that were still more exact. Here Kaufmann was the first to discuss Albert Einstein's theory of special relativity and argued, that although Einstein's theory is based on completely different conditions and is also logically more satisfying, the theory is observationally equivalent to Lorentz's theory. Therefore he spoke of the theory of "Lorentz-Einstein". It is notable that Kaufmann himself interpreted the results of his experiments as a confirmation of Abraham's theory, and a refutation of the Lorentz-Einstein principle of relativity, which for some years weighed heavily against the theories of Lorentz and Einstein. However, Kaufmann's results were criticized by Max Planck and Adolf Bestelmeyer (1906)[2] or Walter Ritz (1908).[3] So physicists like Alfred Bucherer (1908), Neumann (1914) and others, repeated those experiments and arrived at results which apparently confirmed the "Lorentz Einstein" theory and disproved Abraham's theory. However, later it was pointed out that the Kaufmann-Bucherer-Neumann experiments after 1904 were not precise enough to distinguish among the theories.[4][2][5] It lasted until 1940,[6] when such experiments were precise enough to rule out competing models such as Abraham's, and today, the relativistic Lorentz-Einstein relations for momentum and energy are routinely confirmed in particle accelerators, see Tests of relativistic energy and momentum.

However, this problem occurred only for this kind of experiments. The investigations of the fine structure of the hydrogen lines already in 1917 provided a clear confirmation of the Lorentz-Einstein formula, and the refutation of Abraham's theory.[7]

See also[edit]


  1. ^ Hans Kangro (1977), "Kaufmann, Walter", Neue Deutsche Biographie (NDB) (in German) (Berlin: Duncker & Humblo) 11: 352–353 
  2. ^ a b Miller, A.I. (1981), Albert Einstein's special theory of relativity. Emergence (1905) and early interpretation (1905–1911), Reading: Addison–Wesley, ISBN 0-201-04679-2 
  3. ^ Ritz, W. (1908), "Recherches critiques sur l'Ėlectrodynamique Générale", Annales de Chimie et de Physique 13: 260–267 
  4. ^ Zahn, C. T. and Spees, A. A. (1938), "A Critical Analysis of the Classical Experiments on the Variation of Electron Mass", Physical Review 53 (7): 511–521, Bibcode:1938PhRv...53..511Z, doi:10.1103/PhysRev.53.511 
  5. ^ Janssen, M., Mecklenburg, M. (2007), "From classical to relativistic mechanics: Electromagnetic models of the electron", in V. F. Hendricks, et al., Interactions: Mathematics, Physics and Philosophy (Dordrecht: Springer): 65–134 
  6. ^ Rogers, M. M. et al. (1940), "A Determination of the Masses and Velocities of Three Radium B Beta-Particles", Physical Review 57 (5): 379–383, Bibcode:1940PhRv...57..379R, doi:10.1103/PhysRev.57.379 
  7. ^ Pauli, Wolfgang (1921), "Die Relativitätstheorie", Encyclopädie der mathematischen Wissenschaften 5 (2): 539–776 


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