Sagnac effect and pure geometry
arXiv:gr-qc/0401005
Abstract
We show that the Sagnac effect is not necessarily due to the presence of a rotating observer, but rather to the closed path of light in space and an even inertial relative motion between the observer and the physical device forcing light to move along a closed path.
17 pages, 8 figures, added a detailed example in sect. IV, extended and upgraded reference list