Sagnac effect, ring lasers and terrestrial tests of gravity

Light can be used as a probe to explore the structure of space-time: this is usual in astrophysical and cosmological tests; however, it has been recently suggested that this can be done also in terrestrial laboratories. Namely, the Gyroscopes In General Relativity (GINGER) project aims at measuring post-Newtonian effects, such as the gravito-magnetic ones, in an Earth-based laboratory, by means of a ring laser array. Here, we first review the theoretical foundations of the Sagnac effect, on which ring lasers are based, and then, we study the Sagnac effect in a terrestrial laboratory, emphasizing the origin of the gravitational contributions that GINGER aims at measuring. Moreover, we show that accurate measurements allow one to set constraints on theories of gravity different from general relativity. Eventually, we describe the experimental setup of GINGER.