Sagnac, Michelson & Co
Relativity to "touch"
RuedigerRodloff
Background image - DLR - Experimental Laser Gyro - ELSY
What awaits you here ... a short summary:
I have been involved with optical gyros, specifically laser gyros, throughout my professional life.
Experimental-Laserkreiselsystem ELSy - DLR Institute of Flight Guidance
"A Laser Gyro with Optimized Resonator Geometry", R. Rodloff, IEEE JOURNAL OF QUANTUM ELECTRONICS, Vol. QE-23, No.4, APR. 1987
"Does the optical supergyro exist?", Z. Flugwiss. space explorer 18 (1994) 2-15, © Springer Verlag 1994
In addition to the purely technical issues - eg operation of He-Ne gas discharges, stabilization of laser resonators, interferometerie and signal reading,etc. I "stumbled" very often over the physical background of the optical gyros , - densagnac effect.In addition to the Michelson experiment, the Sagnac interferometer forms the starting point for one of the greatest upheavals in our ideas of space and time, - der Theory of Relativity.
There is probably no physical theory that is so controversially discussed as the theory of relativity. Although it is now more than 100 years old, the discussion about it is highly topical and is being conducted with great determination (sd Harold Maurerand other)
But in addition to the "fun" in the scientific debate, the motivation for this website also resulted from some basic considerations about the properties of optical gyros, which are often somewhat neglected in the standard literature._cc781905-5cde-3194 -bb3b-136bad5cf58d_ Eg what role does she playsignal- /lightspeedin the Sagnac interferometer, is it a relativistic effect, what role does the position of the pivot point play?
In the following I will try to answer these fundamental questions - beyond the technical realization - and I hope I can prove thatthe Sagnac effect regardless of the type of signal used (electromagnetic wave, sound wave or any other type of signal transmission) is that it is essentially a relativistic effect and that the apparent contradictions between Sagnac and Michelson within the framework of special relativity (SRT).
First, I would like to briefly introduce the two protagonists of this work:
Georges Sagnac and Albert Abrahm Michelson
You probably knowAA Michelsonfrom school lessons - but do you already have something fromGeorges Sagnacheard ?
OfMichelsoncomes from one of the most important for the physics of the 20th century because"unsuccessful"experiments.
The at first glance very similar experiment*) bysagnachat worked, but is still largely unknown!
This (apparent) contradiction will concern us in what follows.
*) The similarity of the two experiments - especially in the mathematical description - leads to the most adventurous errors in the "lateral thinker scene" to this day.
Georges Sagnac
*14.10. 1869 (Perigeux), † February 26. 1928 (Meudon Belleville), (more)
Georges Sagnac works in the field of X-rays and investigates the propagation of light in 1913rotating systems. **) He was a Knight of the Legion of Honour.
Here is the somewhat confusing sketch of the original experiment.
**) For the sake of completeness it should be mentioned that a comparable experiment was carried out by Franz Harress between 1909 and 1911 - i.e. before Sagnac.
However, his measurement results were not correctly interpreted until 1920 by Max von Laue. (more)
Here is the basic sketch of the Sagnac experiment:
in Quiet
moving
principle sketches
sagnacinterferometer
In this arrangement, the light (represented here by a small blue sphere) first passes through a partially transparent mirror and then hits a beam splitter; There it is divided (yellow and green ball) runs through the circular light guide system, is decoupled again after one revolution and finally superimposed on the first partially transparent mirror.
When the system is at rest (sketch on the left), the two light beams follow exactly the same path after one revolution.
We are now interested in the question of whether a rotational movement of the system (sketch on the right) causes a change in the path between the light wave trains rotating in opposite directions.
Sagnac hadactually a distance difference observed. ( A detailed derivation can be found in the section"Sagnac")
Albert Abraham MIchelson
*19.12. 1852 (Strelno, province of Posen), † 9.5. 1931 (Pasadena California) (more)
Albert Abraham Michelsoninterested in the propagation of light inuniform, rectilinear moving systems. Its -unsuccessful! - Experiments can be considered the starting point for Einstein's theory of relativity and thus for a completely new concept of space and time.*) He dealt with this question for 50 years - from 1881 to the end of his life in 1931 .In 1907 he was the first American to receive the Nobel Prize.
Albert Abraham Michelson
in Quiet
principle sketch
Michelsoninterferometer
moving
A light beam runs from a light source (represented by a small chain of three blue balls) to a beam splitter; there it is split. The two partial beams run perpendicular to each other to a mirror, where they are reflected and then superimposed again at the beam splitter.
Depending on the path length in the two sections, the light waves meet at the beam splitter with a certain path difference - in the example top left (at rest) we have assumed that the two sections are of equal length and that the light wave trains are therefore simultaneous arrive at the beam splitter.
In the event that the system is in motion, Michelson had anticipated that there would be a difference between the two Light wave trains results in a path difference. (A detailed derivation can be found in Section"michelson".)
Michelson could, howeverno difference in distanceobserve.
(Because of its fundamental importance, the experiment is repeated to this day with constantly improving relative accuracy up to 10 exp(-17). S.d. : https://de.wikipedia.org/wiki/Michelson-Morley-Experiment .)
Two experiments - what's the problem?
- in both experiments an attempt is made to measure a speed.
- With the Sagnac interferometer, the circumferential tangential velocity of arotating systembe measured.
- with the Michelson interferometer, the speed of auniformly moving systembe measured.
- in the first case there is a measuring effect, in the second not!
Why ?
Answering this question is one of the exciting chapters in the history of physics.
There have been numerous attempts to reconcile the contradictory results of the two experiments.
The zero result of the Michelson experiment could be explained with a bit of intellectual acrobatics, but then failed because of the positive outcome of the Sagnac experiment or got caught up in contradictions with other findings.
On the following pages I would like to introduce you to a few of these attempts at explanation - not only because it is very exciting to discover the "culprit" or the mistake, like in a crime novel, but also to make it clear that from today's point of view there is only one explanatory model that remains completely consistent - the special theory of relativity.
To get straight to the point: The special theory of relativity stands in in massive contradiction to our everyday experience and is overwhelmed our imagination, but she delivers as the only one a consistent description of the experimental results. The idea, just that
Fehmarn - sunset
Footnote:
In the physics textbooks, the Michelson experiment is usually dealt with in great detail, the Sagnac experiment - if at all - only marginally.
I'm surprised because...
1. Michelson himself predicted the existence of an effect in rotating systems as early as 1904 and saw it as closely related to his own experiment(more on this).
2. The two experiments complement each other in an excellent way as a confirmation of the special theory of relativity, as Max von Laue already in 1911, i.e. 2 years before the implementation of the Sagnac experiment (! ),prove could.
3. The Sagnac effect has - in contrast to the Michelson experiment - a large practical (technical) acquired importance. It is the physical basis for those that have been used successfully in recent years"optical gyroscope", which are used as laser gyros in navigation systems, e.g. in passenger aircraft and submarines.
4. The Sagnac Effect is in contrast to other relativistic effects, it can be experienced macroscopically.
More entertaining is the fact that...
5. The opposite results of both experiments (Michelson negative - Sagnac positive) from thecritics of the Special Theory of Relativity (SRT) are often cited as proof of their invalidity.
