The term gravitational shielding refers to a

hypothetical A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...

process of shielding an object from the influence of a

gravitational field In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenome ...

. Such processes, if they existed, would have the effect of reducing the

weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a Euclidean vector, vector quantity, the gravitational force acting on the object. Others define weigh ...

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 A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...

. The height of the cone's apex above the disk would vary directly with the height of the shielding disk above the earth. Experimental evidence to date indicates that no such effect exists. Gravitational shielding is considered to be a violation of the

equivalence principle In the theory of general relativity, the equivalence principle is the equivalence of gravitational and inertial mass, and Albert Einstein's observation that the gravitational "force" as experienced locally while standing on a massive body (suc ...

and therefore inconsistent with both Newtonian theory and

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...

. The concept of gravity shielding is a common concept in

science fiction Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel unive ...

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 Herbert George Wells"Wells, H. G."
Revised 18 May 2015. ''

The First Men in the Moon''. Wells was promptly criticized for using it by

Jules Verne Jules Gabriel Verne (;''Longman Pronunciation Dictionary''. ; 8 February 1828 – 24 March 1905) was a French novelist, poet, and playwright. His collaboration with the publisher Pierre-Jules Hetzel led to the creation of the ''Voyages extraor ...

Tests of the equivalence principle

, no experiment was successful in detecting positive shielding results. To quantify the amount of shielding, at the beginning of 20th century

Quirino Majorana Quirino Majorana (28 October 1871 – 31 July 1957) was an Italian experimental physicist who investigated a wide range of phenomena during his long career as professor of physics at the Universities of Rome, Turin (1916–1921), and Bologna (192 ...

suggested an extinction coefficient h that modifies Newton's gravitational force law as follows: :

F = \frac e^

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 Poincaré is a French surname. Notable people with the surname include: * Henri Poincaré (1854–1912), French physicist, mathematician and philosopher of science * Henriette Poincaré (1858-1943), wife of Prime Minister Raymond Poincaré * Luci ...

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 Le Sage's theory of gravitation is a kinetic theory of gravity originally proposed by Nicolas Fatio de Duillier in 1690 and later by Georges-Louis Le Sage in 1748. The theory proposed a mechanical explanation for Newton's gravitational force in te ...

, 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.

Majorana's experiments and Russell's criticism

Some shielding experiments were conducted in the early 20th century by

. Majorana claimed to have measured positive shielding effects.

Henry Norris Russell Henry Norris Russell ForMemRS HFRSE FRAS (October 25, 1877 – February 18, 1957) was an American astronomer who, along with Ejnar Hertzsprung, developed the Hertzsprung–Russell diagram (1910). In 1923, working with Frederick Saunders, he deve ...

's analysis of the tidal forces showed that Majorana's positive results had nothing to do with gravitational shielding. To bring Majorana's experiments in accordance with the equivalence principle of General Relativity he proposed a model, in which the mass of a body is diminished by ''the proximity'' of another body, but he denied any connection between gravitational shielding and his proposal of mass variation. For another explanation of Majorana's experiments, see Coïsson et al. But Majorana's results couldn't be confirmed up to this day (see the section above) and Russell's mass variation theory, although meant as a modification of general relativity, is inconsistent with standard physics as well.

Minority views

The consensus view of the scientific community is that gravitational shielding does not exist, but there have been occasional investigations into this topic, such as the 1999 NASA-funded paper which reported negative results.

Eugene Podkletnov Eugene Podkletnov (russian: Евгений Подклетнов, Yevgeny Podkletnov) is a Rossiyane, Russian Ceramic engineering, ceramics engineer known for his claims made in the 1990s of designing and demonstrating gravity shielding devices cons ...

claimed in two papers, one of which he later withdrew, that objects held above a magnetically-levitated, superconducting, rotating disc underwent a reduction of between 0.5 and 2% in weight. Theoreticians have attempted to reconcile Podkletnov's claims with

quantum gravity Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics; it deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the vi ...

theory. However, neither Podkletnov's claims, nor the similar claims of others, of "gravity reduction", "gravity shielding", or the like, have yet been successfully replicated, verified by independent review, or subjected to public demonstration.

Electrets

In his 1976 paper, Electromagnetism and Gravitation, physicist Edward Teller discussed experimentation with electrets, or materials with a permanent

electric dipole moment The electric dipole moment is a measure of the separation of positive and negative electrical charges within a system, that is, a measure of the system's overall polarity. The SI unit for electric dipole moment is the coulomb-meter (C⋅m). The ...

, near its transition point to discover the transition between dipole states. On July 9, 1997, William Rhodes, an inventor, made a posting on Usenet concerning a discovery of an antigravity effect related to electrets. Also, Dr. Martin Tajmar, a physicist and professor for Space Systems at the Dresden University of Technology has written a paper on propellantless propulsion and makes numerous references to electrets. A patent for a gravitational attenuating material that utilizes an organic based material was made by inventor Ronald J. Kita.Gravitational attenuating material Google Patents https://patents.google.com/patent/US8901943B1/en

References

External links