Georges Sagnac (14 October 1869 – 26 February 1928) was a French
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe.
Physicists generally are interested in the root or ultimate cau ...
who lent his name to the
Sagnac effect
The Sagnac effect, also called Sagnac interference, named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferomet ...
, a phenomenon which is at the basis of
interferometers and
ring laser gyroscopes developed since the 1970s.
Life and work
Sagnac was born at
Périgueux
Périgueux (, ; oc, Peireguers or ) is a commune in the Dordogne department, in the administrative region of Nouvelle-Aquitaine, southwestern France.
Périgueux is the prefecture of Dordogne, and the capital city of Périgord. It is al ...
and entered the
École Normale Supérieure
École may refer to:
* an elementary school in the French educational stages normally followed by secondary education establishments (collège and lycée)
* École (river), a tributary of the Seine flowing in région Île-de-France
* École, S ...
in 1889. While a lab assistant at the
Sorbonne
Sorbonne may refer to:
* Sorbonne (building), historic building in Paris, which housed the University of Paris and is now shared among multiple universities.
*the University of Paris (c. 1150 – 1970)
*one of its components or linked institution, ...
, he was one of the first in France to study
X-rays
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nbs ...
, following
Wilhelm Conrad Röntgen
Wilhelm may refer to:
People and fictional characters
* William Charles John Pitcher, costume designer known professionally as "Wilhelm"
* Wilhelm (name), a list of people and fictional characters with the given name or surname
Other uses
* Mount ...
. He belonged to a group of friends and scientists that notably included
Pierre
Pierre is a masculine given name. It is a French form of the name Peter. Pierre originally meant "rock" or "stone" in French (derived from the Greek word πέτρος (''petros'') meaning "stone, rock", via Latin "petra"). It is a translation ...
and
Marie
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* Marie (murder victim), girl who was killed in Florida after being pushed in front of a moving vehicle in 1973
* Marie (died 1759), an enslaved Cree person in Tr ...
Curie,
Paul Langevin
Paul Langevin (; ; 23 January 1872 – 19 December 1946) was a French physicist who developed Langevin dynamics and the Langevin equation. He was one of the founders of the ''Comité de vigilance des intellectuels antifascistes'', an an ...
,
Jean Perrin, and the mathematician
Émile Borel
Félix Édouard Justin Émile Borel (; 7 January 1871 – 3 February 1956) was a French mathematician and politician. As a mathematician, he was known for his founding work in the areas of measure theory and probability.
Biography
Borel was ...
. Marie Curie says that she and her husband had traded ideas with Sagnac around the time of the discovery of radioactivity. Sagnac died at
Meudon-Bellevue.
Sagnac effect
In 1913, Georges Sagnac showed that if a beam of light is split and sent in two opposite directions around a closed path on a revolving platform with mirrors on its perimeter, and then the beams are recombined, they will exhibit interference effects. From this result Sagnac concluded that light propagates at a speed independent of the speed of the source. The motion of the earth through space had no apparent effect on the speed of the light beam, no matter how the platform was turned. The effect had been observed earlier (by Harress in 1911), but Sagnac was the first to correctly identify the cause.
This
Sagnac effect
The Sagnac effect, also called Sagnac interference, named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferomet ...
(in vacuum) had been theoretically predicted by
Max von Laue in 1911. He showed that such an effect is consistent with stationary ether theories (such as the
Lorentz ether theory
What is now often called Lorentz ether theory (LET) has its roots in Hendrik Lorentz's "theory of electrons", which was the final point in the development of the classical aether theories at the end of the 19th and at the beginning of the 20th cen ...
) as well as with Einstein's
theory of relativity
The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in ...
. It is generally taken to be inconsistent with a complete ether drag; and also inconsistent with emission theories of light, according to which the speed of light depends on the speed of the source.
Sagnac was a staunch opponent of the theory of relativity, despite the Sagnac effect being consistent with it.
[Zappe, Hans. (2010). ''Fundamentals of Micro-Optics''. Cambridge University Press. p. 143. ]
See also
*
Sagnac effect
The Sagnac effect, also called Sagnac interference, named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferomet ...
*
History of special relativity#Experiments by Fizeau and Sagnac
References
Further reading
*
*
*
*
Paul Langevin
Paul Langevin (; ; 23 January 1872 – 19 December 1946) was a French physicist who developed Langevin dynamics and the Langevin equation. He was one of the founders of the ''Comité de vigilance des intellectuels antifascistes'', an an ...
, ''Sur la théorie de la relativité et l'expérience de Georges Sagnac'' (1921)
* Paul Langevin, ''Sur l'expérience de Georges Sagnac'' (1937)
*
{{DEFAULTSORT:Sagnac, George
1869 births
1926 deaths
French physicists
Optical physicists
People from Périgueux
Relativity critics
University of Paris alumni