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The '''dynamic theory of gravity''' was an alleged [[unified field theory]] which the distinguished inventor [[Nikola Tesla]] claimed to have constructed late in his life. According to a 1937 press statement by Tesla, he had succeeded in unifying [[gravity]] and [[electromagnetism]].
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Since Tesla never published his own theory, and since no notes describing it in detail seem to be extant, it is impossible to say much about it with certainty. Even the claims allegedly made by Tesla himself before his death, as described below, appear difficult to [[WP:V|verify]]. Tesla's apparently unverifiable claims concerning his own work cannot be said to constitute a contribution to [[theoretical physics]], but they nonetheless remain of absorbing interest to a minority.
==Earlier Work==
In his [[1891]] public lecture on the structure of the [[Luminiferous aether|aether]] and [[electromagnetism]], given at a time when the since discredited notion of the ''luminiferous aether'' was still scientifically respectable, Tesla claimed that there exists ''an infinitesimal world, with molecules and their atoms spinning and moving in orbits, in much the same manner as celestial bodies carrying with them static charges''. Tesla further claimed that ''carriers'' exist transmitting ''"tensions or electrostatic strains"''.
Tesla conducted numerous electromagnetic experiments and patented several devices in the period from [[1892]] to [[1894]], and it is apparently during this time that he may have begun working on his unified field theory. Tesla later claimed to have completed the theory by the late [[1930s]].
==Tesla's description of his theory==
Tesla announced his theory in an unconventional manner. On his 81st birthday ([[July 10]], [[1937]]), he issued a news release asserting that he had "worked out a dynamic theory of gravity" that he soon hoped to give to the world. This statement allegedly read, in part:
: [The Dynamic theory of gravity] ''... explains the causes and motions of heavenly bodies under its influence so satisfactory that it will put to an end idle speculation and false conception, as that of curved space ... '
:''Only the existence of a [[force field|field of force]] can account for the motions of the bodies as observed, and its assumption dispenses with space curvature. All literature on this subject is futile and destined to oblivion. So are all attempts to explain the workings of the universe without recognizing the existence of the ether and the indispensable function it plays in the phenomena ...''
:''There is no energy in matter other than that [[radiant energy|received from the environment]]... It applies rigorously to molecules and atoms as well as the largest heavenly bodies, and to all matter in the universe in any phase of its existence from its very formation to its ultimate disintegration.''
: ''Before the [[electron]] theory was advanced, I had established that [[radiation|radioactive ray]]s consisted of [[Elementary particle|particle]]s of primary matter not further decomposable...''
: ''... The [[kinetic energy|kinetic]] and [[potential energy]] of a body is the result of [[motion (physics)|motion]] and determined by the [[Product (mathematics)|product]] of its [[mass]] and the [[Square (algebra)|square]] of [[velocity]]. Let the mass be reduced, the energy is diminished in the same proportion. If it be reduced to zero the energy is likewise zero for any finite velocity. In other words, it is absolutely impossible to convert mass into energy. It would be different if there were forces in nature capable of imparting to a mass infinite velocity. Then the product of zero mass with the square of infinite velocity would represent infinite energy. But we know that there are no such forces and the idea that mass is convertible into energy is rank nonsense.''<small><sup>[1]</sup></small>
Tesla allegedly said that his theory explained [[gravitation]] as a mixture of [[transverse wave|transverse]] and [[longitudinal wave|longitudinal]] electromagnetic waves.
For comparison, in the language of mainstream physics, [[electromagnetic wave]]s as treated in [[Maxwell's theory of electromagnetism]] are said to be ''spin-one'' and ''purely transverse'', while in [[general relativity]], [[gravitational wave]]s are said to be ''spin-two'' and ''purely transverse''. Thus, in Maxwell's theory there are no longitudinal electromagnetic waves, while in general relativity, despite some useful conceptual similarities, the gravitational field effect (of a mass deforming spacetime) is distinct from electromagnetic radiation. Also, while in Maxwell's theory the effects of the electromagnetic field on charged test particles is treated by the [[Lorentz force law]], in general relativity the effects of the gravitational field on test particles is treated very differently: the kinematical history of a test particle is represented by a [[timelike]] [[geodesic]] in a [[Lorentzian manifold]], while, roughly speaking, the kinematical history of a photon is represented by a [[null geodesic]].
==Tesla's views on special and general relativity==
Tesla was an outspoken critic of [[relativity theory]], vehemently rejecting the notion that energy could be obtained from "conversion" of rest mass long after mainstream physicists had accepted this.
In a popular article published in [[1934]], Tesla (perhaps anticipating modern complaints concerning [[string theory]]) charged physicists with substituting mathematical speculation for experiments, and expressed the fear that the result would be theories bearing no relation to physical reality.<small><sup>[4]</sup></small>
In his 1937 press statement, Tesla criticized the notion of [[curved spacetime]], saying in part:
:''... Supposing that the bodies act upon the surrounding space causing curving of the same, it appears to my simple mind that the curved spaces must react on the bodies, and producing the opposite effects, straightening out the curves. Since action and reaction are coexistent, it follows that the supposed curvature of space is entirely impossible - But even if it existed it would not explain the [[Celestial mechanics|motions of the bodies]], as observed.'' <small><sup>[1]</sup></small>
This statement appears to reflect misconceptions concerning [[Albert Einstein]]'s theory of gravitation:
*General relativity does give a self-consistent description of the motion of celestial bodies.
*In 1937, Einstein, Infeld, and Hoffman argued that description in terms of geodesics of the motion of massive objects immersed in a gravitation field follows from the [[Einstein field equation]] of general relativity. To be fair, these arguments are not easy, and physicists to this day continue to try to improve them. However, they are generally regarded as essentially correct and can be supported.
Tesla's 1937 announcement appears to have made little or no impression upon contemporary physicists, perhaps because his statement appears to have been too vague to guess very much about the nature of his alleged theory, and appears to have been couched in language which was already receding into the distant past.
Extensive experimental testing of general relativity did not begin until about [[1960]]; furthermore, essential theoretical features of general relativity were not well understood until about this time. (See [[Golden age of general relativity]] for more information about events in the period 1960-1975 which firmly established general relativity as our gold standard theory of gravitation.) Therefore, in 1937 general relativity was not quite so solid an experimental footing as it is today. By 1937 most astronomers and physicists had long accepted that general relativity gives an accurate description of solar system dynamics to within the accuracy of observation and experiment. Tesla's murky description of his unified field theory could perhaps have been described as ''fringe science'' in 1937. Today it could only be described as ''[[not even wrong]]''.
== See also ==
*[[Classical theories of gravitation]], for some mainstream competitors of general relativity
*[[List of alternative, speculative and disputed theories#Physics|List of fringe physics theories]]
== References ==
: ''[1]'' : Tesla, Nikola, "''[http://www.tesla.hu/tesla/articles/19370710.doc Tesla press statement]''". July 10, 1937.
: ''[2]'' : Seifer, Marc J., "''Wizard, the Life and Times of Nikola Tesla''". ISBN 1-559723-29-7
: ''[3]'' : O'Neill, John H., "''Prodigal Genius''". ISBN 0-914732-33-1
: ''[4]'' : Tesla, Nikola, "''Radio Power Will Revolutionize the World''". Modern Mechanics and Inventions, July, 1934.
==External links==
* [http://www.crank.net/physics.html Crank Dot Net] lists many cranky websites (and some ''anti-crank sites'' which attempt to counter the excesses of pseudophysics).
* [http://peswiki.com/index.php/PowerPedia:Tesla%27s_Dynamic_Theory_of_Gravity Tesla's Dynamic Theory of Gravity], from [http://peswiki.com PowerPedia], a wiki apparently maintained by one Sterling Allan, which promotes various schemes for generating huge amounts of cheap or free energy, by means unknown to mainstream physics.
* [http://www.rense.com/general10/deathray.htm Tesla's claim] to possess a [[death ray]], reprinted from the [[New York Times]].
[[Category:Nikola Tesla]]
[[Category:Pseudophysics]]
[[Category:Accuracy disputes]]
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