GRAVITOMAGNETISM AND THE SPEED OF GRAVITY

Abstract

Experimental discovery of the gravitomagnetic fields generated by translational and/or rotational currents of matter is one of primary goals of modern gravitational physics. The rotational (intrinsic) gravitomagnetic field of the Earth is currently measured by the Gravity Probe B. The present paper makes use of a parametrized post-Newtonian (PN) expansion of the Einstein equations to demonstrate how the extrinsic gravitomagnetic field generated by the translational current of matter can be measured by observing the relativistic time delay caused by a moving gravitational lens. We prove that measuring the extrinsic gravitomagnetic field is equivalent to testing the relativistic effect of the aberration of gravity caused by the Lorentz transformation of the gravitational field. We show that the recent Jovian deflection experiment is a null-type experiment testing the Lorentz invariance of the gravitational field (aberration of gravity), thus, confirming existence of the extrinsic gravitomagnetic field associated with the orbital motion of Jupiter with accuracy 20%. We comment on physically inadequate interpretations of the Jovian deflection experiment given by a number of researchers who are not experts in modern VLBI techniques and the subtleties of JPL ephemeris. We propose to measure the aberration of gravity effect more accurately by observing the gravitational deflection of light by the Sun and processing VLBI observations in the geocentric frame with respect to which the Sun is moving with velocity ~30 km/s.