Reinventing Gravity - John W.Moffat

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In 1916, Einstein published his new theory of gravity called general  relativity. In 1919, the theory was validated by the observation of the bending of light during a solar eclipse, as the sun’s gravitational pull warped spacetime. Since then, there has been much speculation as to whether Einstein’s theory of gravity is perfect and unchangeable, much like Michelangelo’s David. Why would we want to modify Einstein’s outstanding intellectual achievement?

Until recently, most physicists have considered Einstein’s general relativ-ity theory to be in perfect agreement with observational data. However, this is not necessarily true. Neither have the attempts succeeded to unify Ein-stein’s gravitational theory with quantum mechanics, despite much effort:  Many physicists consider the search for a successful quantum gravity theory the holy grail of modern physics. Moreover, there are some fundamentally unsatisfactory features of Einstein’s theory, such as those related to the be-ginning of the universe and the collapse of stars under their own gravita-tional forces.

Finally, since the early 1980s, a growing amount of observational data has been accumulating that shows that Newtonian and Einstein gravity cannot describe the motion of the outermost stars and gas in galaxies correctly if only their visible mass is accounted for in the gravitational field equations.*

There are much stronger gravitational forces being observed—causing the peripheral orbiting stars and gas to move faster—than are predicted by New-ton’s and Einstein’s theories. There is now overwhelming evidence for stronger gravity in galaxies. To put this in perspective, consider that Einstein’s correction to Mercury’s orbit, which constituted a major test for general rela-tivity theory in 1915, was tiny, representing only 43 arc seconds per century. In contrast, the discrepancy between the rotational speeds of stars in the outermost parts of giant spiral galaxies and the predictions of the prevailing theories of gravity is enormous: The stars are moving at about  twice the speed that they should be, according to Newtonian and Einstein gravity.  Einstein’s gravity theory reduces to Newton’s theory for weak gravitational fields and slowly moving bodies.