CELESTIAL OPTICAL INTERFEROMETRY: A NEW TOOL FOR ULTRAHIGH PRECISION STUDIES IN GRAVITY

Abstract

The tremendous progress in the science and technology of timing devices and laser sources has reached a stage where their stability and coherence are sufficient for implementing unbalanced interferometers over a length scale exceeding the Earth–Moon distance. This opens up the possibility of optical homodyne interferometry over such distances, either to the Moon or to artificial satellites that are at large distances from the Earth. The precision of the measurement of changes in the orbital distance would increase by a factor of 104 or more, enabling new ultrahigh precision tests of the equivalence principle, study of gravitomagnetism, and of subtle gravitational phenomena, including the constancy of the gravitational constant and possible gravitational expansion of space. It would enable geodesy and tide studies with unprecedented precision. Such interferometers would also be useful for the detection and study of low frequency gravitational waves.