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The term gravitational shielding refers to a hypothetical process of shielding an object from the influence of a gravitational field. Such processes, if they existed, would have the effect of reducing the weight of an object. The shape of the shielded region would be similar to a shadow from the gravitational shield. For example, the shape of the shielded region above a disk would be conical. The height of the cone's apex above the disk would vary directly with the height of the shielding disk above the earth.〔Unnikrishan, C. S. (1996). Does a superconductor shield gravity? ''Physica C'', 266, 133-137.〕 Experimental evidence to date indicates that no such effect exists. Gravitational shielding is considered to be a violation of the equivalence principle and therefore inconsistent with both Newtonian theory and general relativity.〔Bertolami, O. & Paramos, J. & Turyshev, S. G. (2006), (General Theory of Relativity: Will it survive the next decade? ), in H. Dittus, C. Laemmerzahl, S. Turyshev, Lasers, Clocks, and Drag-Free: Technologies for Future Exploration in Space and Tests of Gravity: 27-67〕 The concept of gravity shielding is a common concept in science fiction literature, especially for space travel. One of the first and best known examples is the fictional gravity shielding substance "Cavorite" that appears in H. G. Wells' classic 1901 novel ''The First Men in the Moon''. Wells was promptly criticized for using it by none other than Jules Verne.〔 "I sent my travelers to the moon with gunpowder, something one sees every day. Where is Monsieur Wells' 'Cavorite'? Let him show it to me!"〕 == Tests of the equivalence principle== , no experiment was successful in detecting positive shielding results. To quantify the amount of shielding, Quirino Majorana〔Majorana, Q., (1920). “On gravitation. Theoretical and experimental researches”, ''Phil. Mag.'' (6 ) 39, 488-504.〕 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.〔Unnikrishnan and Gillies (2000), Phys Rev D, 61〕 Another recent analysis suggested a lower bound of 0.6×10−15.〔Caputo M., On new limits of the coefficient of gravitation shielding,J. Astrophysics and Astronomy,vol. 27, 439-441 (2006).〕 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.〔Yang X.-S., Wang Q.-S., Gravity Anomaly During the Mohe Total Solar Eclipse and New Constraint on Gravitational Shielding Parameter,Astrophysics and Space Science, Vol.282, 245-253 (2002).〕 However, astronomical observations impose much more stringent limits. Based on lunar observations available in 1908, Poincaré〔Poincaré, H. (1908). "La dynamique de l'électron", ''Revue générale des sciences pures et appliquées 19'', pp. 386-402, reprinted in Science and Method. Flammarion, Paris. An English translation was published as Foundation of Science, Science Press, New York, 1929.〕 established that h can be no greater than 10−18 m²/kg. Subsequently this bound has been greatly improved. Eckhardt〔D. H. Eckhardt, Phy Rev D, 42, 1990, 2144〕 showed that lunar ranging data implies an upper bound of 10−22 m²/kg, and Williams, et al.,〔Williams, et al., “Testing the Equivalence Principle on the Ground and in Space”, (2006), to be published by Springer Verlag, Lecture Notes in Physics, gr-qc/0507083〕 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.〔Unnikrishnan, Mohapatra, Gillies (2002), “Anomalous gravity data during the 1997 total solar eclipse do not support the hypothesis of gravitational shielding”, Physical Review D, vol 63, available online at http://www.astro.oma.be/ICET/bim/bim138/vanruymbeke2.htm〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravitational shielding」の詳細全文を読む スポンサード リンク
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