The Sagnac effect in superfluids

We comment on the interpretation of absolute rotation measurements with superfluids, which involve the Sagnac effect. This effect, first observed in rotating optical interferometers, has now been seen in a host of different physical systems, ranging from atomic clocks to electrons, neutrons, atomic beams, ... We show that the time-honored explanation of this effect based on general relativity provides a common explanation for all these systems, including superfluids, in contradistinction with the views expressed in a recent review article.