Methodology and instrumentation for testing the weak equivalence principle in stratospheric free fall

Abstract

The use of the GiZero free-fall facility for testing the weak equivalence principle is discussed in this article. GiZero consists of a vacuum capsule, released from a balloon at an altitude of 40 km, which shields an experimental apparatus free falling inside the capsule itself. The expected residual acceleration external to the detector is 10−12 g (with g the Earth’s gravitational acceleration) for the 30 s free fall. A common-mode rejection factor of about 10−4 reduces the residual noise differential output to only 10−16 g. The gravity detector is a differential accelerometer with two test masses with coincident center of masses (i.e., zero baseline) with capacitive pick ups. Preparatory experiments have been conducted in the laboratory with a precursor detector by measuring controlled gravity signals, at low frequency, and by observing the Luni-Solar tides. The estimated accuracy in testing the weak equivalence principle, with a 95% confidence level, is 5×10−15 in a 30 s free fall. When compared to orbital free-fall experiments, the GiZero experiment can be considered as a valid compromise which is able to satisfy the requirement for improving significantly the experimental accuracy in testing the equivalence principle with a substantial lower cost, the ability to recover the detector and to repeat the experiment at relatively short time intervals.

Relevance of the weak equivalence principle and experiments to test it: Lessons from the past and improvements expected in space

“…A longer free fall time would help, since the effect of a violation increases quadratically with time. Drop tests using balloons and sounding rockets have been proposed [41,42]. In [42] the plan was to make drops with reversed axis in order to distinguish the effect of gravity gradient.…”

General Relativity Accuracy Test (GReAT): New configuration for the differential accelerometer

“…Consequently, a possible violation of the UFF will be detected by differential accelerations measurements. A differential accelerometer (Iafolla et al, 1998) is then an ideal probe to test for possible violations of the WEP. The detector must have a very high sensitivity to differential accelerations acting on a pair of proof-masses of different materials.…”

“Galileo Galilei” (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein

“…All other experiment proposals aiming at a considerable improvement over the results achieved by rotating torsion balances are to be performed inside a capsule dropped during a balloon flight [17], in a suborbital flight with a sounding rocket [18] or inside a spacecraft in low Earth orbit [19][20][21].…”