von Franco Selleri
The Sagnac Effect, Once More
Dipartimento di Fisica, Università di Bari INFN, Sezione di Bari [Italien]
A simple and rigorous proof of the Sagnac effect for the most general value of the synchronization parameter e1 is given. If in the final result one adopts the relativistic e1
one can see that the relativistic theory is incompatible with the experimental evidence. Only the theory with e1 = 0 predicts correctly the Sagnac effect. Of course the obtained results depend on the assumptions made, which look rather safe however.
In the 1913 Sagnac experiment  a platform rotated uniformly at a rate of 1-2 rot/sec. In an interferometer mounted on the platform, two interfering light beams, reflected by mirrors, propagated in opposite directions along a closed horizontal circuit. The rotating system included also the luminous source and a photographic plate recording the interference fringes. Sagnac observed a shift of the interference fringes every time rotation was modified. This shift depends on the relative time delay delta t , object of our calculations, with which the two light beams (better: localized light pulses) reach the detector.
Authoritative attempts at explaining the Sagnac observations in terms of the relativistic theories were made by Langevin , Post  and Landau and Lifschitz , but they all found it impossible to carry through a purely deductive argument and added arbitrary additional assumptions with a big loss of generality. Almost a century after the 1913 discovery of the Sagnac effect no justification of it exists based on special and/or general relativity. Hasselbach and Nicklaus (1993) list about 20 different “explanations” of the effect and comment:
- 17. September 2012