Hoyle-Narlikar theory of gravity

The Hoyle–Narlikar theory of gravity is a Machian and conformal theory of gravity proposed by Fred Hoyle and Jayant Narlikar that originally fits into the quasi steady state model of the universe. The gravitational constant G is arbitrary and is determined by the mean density of matter in the universe. The theory was inspired by the Wheeler–Feynman absorber theory for electrodynamics. When Feynman, as a graduate student, lectured on the Wheeler–Feynman absorber theory in the weekly physics seminar at Princeton, Einstein was in the audience and stated at question time that he was trying to achieve the same thing for gravity.

Stephen Hawking showed in 1965 that the theory is incompatible with an expanding universe, because the Wheeler-Feynman advanced solution would diverge. However at that time the accelerating expansion of the universe was not known, which resolves the divergence issue because of the cosmic event horizon. The discovery of the accelerated expansion is fairly recent and it earned the Nobel prize in 2011.

The Hoyle-Narlikar theory reduces to Einstein's general relativity in the limit of a smooth fluid model of particle distribution and a transformation of coordinates into the rest frame of the fluid to simplify the field equations. The two theories make the same predictions and the Hoyle-Narlikar theory has been shown to be correct according to various cosmological tests.

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