ATTENTION !!! CHANGEMENT DE SALLE !!! Relativistic theory of a falling cube ravimeter

Orateur : Neil ASHBY (National Institute of Standards and Technology (NIST), Boulder, Colorado, USA)

We give a relativistic treatment of interference between light reflected from a falling cube retroreflector in the vertical arm of an interferometer, and light in a reference beam in the horizontal arm. Coordinates that are nearly Minkowskian, attached to the falling cube, are used to describe the penetration of the light into the cube. Relativistic effects such as the dependence of the coordinate speed of light on gravitational potential, propagation of light along null geodesics, relativity of simultaneity, and Lorentz contraction of the moving cube, are accounted for. The calculation is carried to first order in the gravity gradient. Analysis of data from a falling cube gravimeter shows that the propagation time of light within the cube itself causes a significant reduction in the value of the acceleration of gravity obtained from measurements, compared to assuming reflection occurs at the front face. An expression for this correction is derived and compared with data from several thousand drops. Depending on the instrument, the correction can be several $\mu$Gal, comparable to commonly applied corrections such as those due to polar motion and earth tides. The controversial ’speed of light’ correction is discussed.

Télécharger dans mon agenda