Emil Cohn
Emil (Georg ) Cohn ( born September 28, 1854 in Neustrelitz; † 28 January 1944 Ringgenberg, Kanton Bern, Switzerland ) was a German physicist.
Life
Emil Cohn's parents were August Cohn (* 1826, lawyer in Neustrelitz ) and Charlotte Cohn, nee Hahn ( 1835-1924 ). At 17, Emil Cohn had first started at the University of Leipzig in order to study law. He turned then, however, soon the natural sciences and continued his studies at the Universities of Heidelberg and Strasbourg continued. In Strasbourg, he received his doctorate in 1879, Dr. phil. nat. From 1881 to 1884 he was an assistant from August Kundt at the Physics Institute. On 5 February 1884 he completed his habilitation in Theoretical Physics and was admitted as a private. From 1884 to 1918 he was a faculty member of the University of Strasbourg. On September 27, 1884, he was appointed assistant professor. He dealt first with experimental physics, but then turned very theoretical physics. In 1918 he was appointed extraordinary professor.
After the end of World War II and the occupation of Alsace-Lorraine by France Cohn was expelled with his family from Strasbourg ( Christmas Eve 1918). In April 1919 he was appointed at the University of Rostock for ordinary honorary professor. From June 1920 he held as ordinary honorary professor at the University of Freiburg Lectures on Theoretical Physics. In 1935, he sat down to rest in Heidelberg, where he lived until 1939. Under the impression of arbitrariness of the Nazi regime, he declared in 1938, together with Richard Gans, Leo Graetz, George Jaffe, Walter Kaufmann ( physicist ) and other physicists " Israelite descent" opposite Peter Debye demonstratively his withdrawal from the German Physical Society ( DPG).
Cohn was Protestant and baptized with Marie Goldschmidt (1864-1950) married, with whom he had two daughters. Because of his " Israelite descent" he saw in 1939 forced under pressure from the Nazi dictatorship to emigrate to Switzerland. He lived there first in Hasliberg Hohfluh, from 1942, in Ringgenberg on Lake Brienz.
Cohn's younger brother Carl Cohn (1857-1931) was a successful overseas Hamburg merchant, who worked 1921-1929 as Hamburg senator.
Work
Cohn counted at the turn of the 19th to 20th centuries the most respected experts in the field of theoretical electrodynamics. He was dissatisfied for moving bodies with the Lorentz electrodynamics by Hendrik Antoon Lorentz and hit his own theory before. His alternative theory, which was based on a modification of Maxwell's macroscopic field equations without taking into account the atomic structure of matter, was at that time with all the relevant electrodynamic and optical experiments in line with the Michelson -Morley experiment. He rejected the Lorentz contraction, however, took the concept of local Lorentz. Cohn's theory was further developed in 1905 by Richard Gans and applied to the electron theory.
In 1900 he used the term " Lorentz transformation ", where Henri Poincaré finally in 1905 used the term to use today Lorentz transformation. Some of his insights took certain aspects of Albert Einstein's special relativity theory (SRT ) in advance, such as the abandonment of the concept of the " luminiferous ether ", which he replaced with the fixed stars as the reference system (1901 ). Although Cohn curtailed that it was possibly for reasons of clarity heuristically useful to think of the Fixerstensystem than in a substantial "ether" dormant, but this was only imagery that adds nothing to his theory of content. And as he interpreted Poincaré 1904, the Lorentz local time as the time which arises under the assumption of a constant speed of light - which Cohn coined the picture, according to which light propagates as a spherical wave in all systems. He also illustrated before Einstein Lorentz contraction and time dilation effects as with rods and clocks. He also noted that at least on the ground of Lorentz's theory the distinction between universal and local time artificial forms, almost as in this theory, no experimental difference between them can be made. Cohn himself believed, however, that Lorentz's assumption is anyway only valid for optical effects, whereas according to his own theory of mechanical watches might indicate "absolute" time.
However, Cohn's theory could be partly due to internal disagreements, not prevail against the theories of Lorentz and Einstein. So contradicted his theory to the reaction principle and the principle of relativity. Also believed Cohn, the velocity with respect to the fixed star background would be an absolute speed. In addition, his theory predicted different results for the Michelson -Morley experiment, depending on the direction in certain media advance. Cohn himself later accepted (1911 ) the " principle of relativity by Lorentz and Einstein" and drew up a representation of the SRT, which was endorsed by Einstein.