Talk:Sagnac effect

mode locking
The article says: The beat frequency will be zero if and only if the ring laser setup is non-rotating with respect to inertial space. just before the section named lock-in. (I would have called it mode-locking, but lock-in is probably fine.) But note that in the lock case, the beat is also zero, so the IFF is wrong. Otherwise, it seems to me that the effect of mode locking isn't discussed much in the article, and even less in this talk page. Many imperfections, such as dust on the mirrors, can mix the beams, and increase the lock effect. Gah4 (talk) 21:37, 22 January 2019 (UTC)

= c ===

Just want to say that I'm not totally happy with the definition of why light 'slowed down' in this sentence " The reason for looking at General Relativity is because Einstein's Theory of General Relativity predicted that light would slow down in a gravitational field which is why it could predict the curvature of light around a massive body." Isn't it also so that it is the geometry that makes an earthly observer define light as 'slowed down', meaning that the geodesic adapt to gravity? If so 'c' should be 'c' even in a gravitational potential, or is there something I'm missing here? — Preceding unsigned comment added by 185.113.96.62 (talk) 23:00, 7 February 2019 (UTC)

Also, although I can see the geometrical approach presented in letting light 'meet' relatively 'chase' the rings rotation I still wonder about it. The 'acceleration' presented by its rotation should go both ways as it seems to me? Just as deceleration and a acceleration becomes a equivalence? Maybe one instead should break it down in how many 'reflections/steps' the light signals would have to do to 'bounce' from source to sink and thereby define a path length and time? Or am I bicycling in the great yonder here? — Preceding unsigned comment added by 185.113.96.62 (talk) 23:44, 7 February 2019 (UTC)

How it works is unclear to a non-expert
"However, when the interferometer system is spun, one beam of light has a longer path to travel than the other in order to complete one circuit of the mechanical frame, and so takes longer, resulting in a phase difference between the two beams." How is that? Tuntable (talk) 07:50, 8 April 2019 (UTC)


 * I suspect it isn't so obvious, even to experts. If you take, for example, a rotating tube of water, such that the water inside rotates with the tube, and send sound waves though it, they will move at the speed of sound in the moving fluid. But light doesn't work that way. You can see, though, that when it is rotating, that the distance light travels to the next mirror is longer or shorter, as the mirror will have moved from the time the light leaves one to when it arrives at the next one. Gah4 (talk) 14:54, 8 April 2019 (UTC)

I think that maybe it rotates in the same plane as the light, not like a gyroscope? If so, then that should be said. Tuntable (talk) 07:50, 8 April 2019 (UTC)


 * Yes it senses rotation around an axis perpendicular to the light travel plane. Gah4 (talk) 14:54, 8 April 2019 (UTC)

Merge proposal
I propose redirecting Franz Harress here. He seems to be only remembered for his Sagnac effect experiments, and there is little to be said about him beyond that. Jähmefyysikko (talk) 05:10, 28 October 2023 (UTC)


 * ✅ Done. Jähmefyysikko (talk) 14:07, 21 December 2023 (UTC)


 * What could have been a promising scientific career was cut short by WWI. As it is, all we have of Harress' work is his doctoral thesis on the propagation of light in moving glass (which showed excellent technique, but which was marred by a calculation error). Harress' doctoral adviser, Otto Knopf, published a posthumous presentation of his work (with corrections) in Annalen der Physik. Prokaryotic Caspase Homolog (talk) 11:19, 24 December 2023 (UTC)