# Gravitational Shielding - Tests of The Equivalence Principle

Tests of The Equivalence Principle

As of 2008, no experiment was successful in detecting positive shielding results. To quantify the amount of shielding, Quirino Majorana suggested an extinction coefficient h that modifies Newton’s gravitational force law as follows:

The best laboratory measurements have established an upper bound limit for shielding of 4.3×10−15 m²/kg. Another recent analysis suggested a lower bound of 0.6×10−15. The best estimate based on the most accurate gravity anomaly data during the 1997 solar eclipse has provided a new constraint on the shielding parameter 6×10−19 m²/kg. However, astronomical observations impose much more stringent limits. Based on lunar observations available in 1908, Poincaré established that h can be no greater than 10−18 m²/kg. Subsequently this bound has been greatly improved. Eckhardt showed that lunar ranging data implies an upper bound of 10−22 m²/kg, and Williams, et al., have improved this to h = (3 ± 5)×10−22 m²/kg. Note that the value is smaller than the uncertainty. The consequence of the negative results of those experiments (which are in good agreement with the predictions of general relativity) is, that every theory which contains shielding effects like Le Sage's theory of gravitation, must reduce those effects to an undetectable level. For a review of the current experimental limits on possible gravitational shielding, see the survey article by Bertolami, et al. Also, for a discussion of recent observations during solar eclipses, see the paper by Unnikrishnan et al.

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