Suppressing radial non-observability in a concentric two-sphere equivalence-principle experiment by gravity-gradient cancellation

摘要

A design for an equivalence-principle experiment in a drag-free satellite using two free-falling concentric spheres is discussed. In addition to the problem of measuring the positions fo the spheres, this approach suffers from the difficulty that a small radius error can not be distinguished from a violation fo the equivalence principle (EP) and the response to an EP violation only grows as t not t~2. Both of these problems can be solved by adding heavy masses on each side of the cavity to cancel the earth's gravity gradient and the differential centrifugal force. The resulting system could detect a violation of the equivalence principle between 10~-20 and 10~-24 g. Although the experiment is located in a satellite orbiting the earth, it is equivalent to a very tall (0.1 to 10 Au) drop tower with drop times between 10~5 and 10~6 seconds and an effective value of g equal to about 3.4 meters/sec~2 which is 3/7 of the value of g at the orbital altitude.