Emil Georg Cohn (28 September 1854 – 28 January 1944), was a German physicist. Contents 1 Life 2 Work 3 Sources 4 Publications Life[edit]
Cohn was born in Neustrelitz,
Further information: History of special relativity At the beginning of the 20th century, Cohn was one of the most
respectable experts in the area of theoretical electrodynamics. He was
unsatisfied with the Lorentzian theory of electrodynamics for moving
bodies and proposed an independent theory. His alternative theory,
which was based on a modification of the Maxwell field-equations, was
compatible to all relevant electrodynamic and optical experiments
known at that time (1900–1904), including the Michelson-Morley
experiment (MMX) of 1887. Cohn's electrodynamics of moving bodies was
based on the assumption that light travels within the Earth's
atmosphere with a constant velocity - however, his theory suffered
from internal failures. While the theory predicted the negative result
of MMX within air, a positive result would be expected within vacuum.
Another weak point stems from the fact, that his concept was
formulated without the use of atoms and electrons. So after 1905 his
theory was superseded by Hendrik Lorentz's and Albert Einstein's.[2]
[3] [4][5]
Regarding his own theory (developed in 1900 and 1901), he used the
Everywhere, where the propagation of radiation is not the object of measurement, we define identical moments of time at different points of Earth's surface, by treating the propagation of light as timeless. In optics, however, we define these identical moments of time by assuming, that the propagation takes place in spherical waves for every relatively resting and isotropic medium. This means: the "time" which actually serves us for the representation of terrestrial processes, is the "local time" t ′ displaystyle t' , for which the equations I'b to IVb hold, – not the "general time" t displaystyle t .[8] — Emil Cohn, 1904 He also illustrated the effects of length contraction and time dilation by using moving rods and clocks. x 0
y 0
z 0 displaystyle x_ 0 y_ 0 z_ 0 are those measuring numbers being read at an "initially correct" measuring-rod (initially = when at rest), after it was introduced into the system and was accordingly deformed. [...] t 0 displaystyle t_ 0 are those time intervals indicated by an "initially correctly ticking" clock, after it was inserted into the system and accordingly has changed its rate.[9] — Emil Cohn, 1904 He critically remarked that the distinction between "true time" and "local time" in Lorentz's theory is artificial, because it cannot be verified by experiment. However, Cohn himself believed that the validity of Lorentz's theory is limited to optical phenomena, whereas in his own theory it is possible that mechanical clocks might indicate the "true" time.[10][11] Later in 1911 (after his own theory was disproved), Cohn accepted the relativity principle of "Lorentz and Einstein" and wrote a summary on special relativity, which was applauded by Einstein.[12] Sources[edit] ^ Fritz Emde (1947). "Nachruf auf Emil Cohn". Archiv der Elektrischen
Übertragung. 1 (1–2): 81–83.
^ Darrigol, O., Olivier (1995). "Emil Cohn's electrodynamics of moving
bodies". American Journal of Physics. 63 (10): 908–915.
Bibcode:1995AmJPh..63..908D. doi:10.1119/1.18032.
^ Darrigol, Olivier (2000).
Publications[edit]
Cohn, E. (1900). Das Elektromagnetische Feld - Vorlesungen über die Maxwell'sche Theorie. Leipzig: S. Hirzel. ; Second edition Berlin 1927: Das elektromagnetische Feld - Ein Lehrbuch Cohn, E. (1900). "Über die Gleichungen der Electrodynamik für bewegte Körper". Recueil de travaux offerts par les auteurs à H. A. Lorentz à l’occasion du 25ème anniversaire de son doctorat le 11 décembre 1900, Archives néerlandaises. 5: 516–523. Cohn, E. (1901). "Über die Gleichungen des elektromagnetischen Feldes für bewegte Körper". Göttinger Nachrichten: 74–99. Cohn, E. (1901). "Ueber die Gleichungen des elektromagnetischen Feldes für bewegte Körper". Annalen der Physik. 312 (1): 29–56. Bibcode:1901AnP...312...29C. doi:10.1002/andp.19013120103. Cohn, E. (1904). "Zur Elektrodynamik bewegter Systeme I". Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften. 1904 (40): 1294–1303.
Cohn, E. (1904). "Zur Elektrodynamik bewegter Systeme II". Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften. 1904 (43): 1404–1416.
Cohn, E (1904). "Antikritisches zu Hrn. Wiens "Differentialgleichungen der Elektrodynamic für bewegte Körper"". Annalen der Physik. 14 (6): 208. Bibcode:1904AnP...319..208C. doi:10.1002/andp.19043190619. "Physikalisches über Raum und Zeit", Himmel und Erde XIII, 117–136 (1911); auch als Broschüre veröffentlicht: Physikalisches über Raum und Zeit, Berlin/Leipzig 1920, 4. Auflage (30 S.). "Faraday und Maxwell", Deutsches Museum - Abhandlungen und Berichte 4 (1), Berlin 1932 (29 S.). Authority control WorldCat Identities VIAF: 333294 LCCN: n2011002688 ISNI: 0000 0001 1034 8201 GND: 116629150 SUDOC: 129338702 BNF: cb15611095v (data) SN |