G. Catastini

On the universality of free fall, the equivalence principle, and the gravitational redshift

Through the contributions of Galileo, Newton, and Einstein, we recall the universality of free fall (UFF), the weak equivalence principle (WEP), and the strong equivalence principle (SEP), in order to stress that general relativity requires all test masses to be equally accelerated in a gravitational field; that is, it requires UFF and WEP to hold. The possibility of testing this crucial fact with null, highly sensitive experiments makes these the most powerful tests of the theory. Following Schiff, we derive the gravitational redshift from the WEP and special relativity and show that, as long as clocks are affected by a gravitating body like normal matter, measurement of the redshift is a test of UFF/WEP but cannot compete with direct null tests. A new measurement of the gravitational redshift based on free-falling cold atoms and an absolute gravimeter is not competitive either. Finally, we compare UFF/WEP experiments using macroscopic masses as test bodies in one case and cold atoms in the other. We con...

Test of the equivalence principle in a non-drag-free spacecraft

Abstract In a near Earth orbit the driving force of a possible violation of the equivalence principle is a factor 500 larger than it is on the ground. A passive attenuator allows one to reduce the high acceleration noise of the space structure, hence to perform the experiment in a non-dedicated, non-drag-free spacecraft. By means of piezoelectric rotating sensors, with frictionless diamagnetic bearings, it is possible to test the equivalence principle at room temperature to 3×10 −15 , about three orders of magnitude better than achieved so far.

Noise attenuators for gravity experiments in space

Abstract Space is highly advantageous for small force experiments. However, they are seriously limited by spacecraft vibrational noise. We present a passive attenuator which allows one to realize a noise-free laboratory inside any flying structure. The attenuator works between a fraction of 1 Hz and 1000 Hz. In the two-stage version the residual disturbance can be 10 -10 cm s -2 with very short integration times. A third stage makes it even lower.

`Galileo Galilei' on the ground (GGG)

GGG is a supercritical rotor to test, on the ground, the equivalence principle to one part in and to prepare for the space experiment.