A Look at the Abandoned Contributions to Cosmology of Dirac, Sciama and Dicke

The separate contributions to cosmology of the above researchers are revisited and a cosmology encompassing their basic ideas is proposed. We study Dirac’s article on the large number hypothesis (Proc.Roy.Soc. Lon. A 165,199; 1938), Sciama’s proposal of realizing Mach’s principle (MNRAS 113, 34; 1953), and Robert Dicke’s considerations on an ‘electromagnetic’ theory of gravitation with a variable speed of light (Rev.Mod.Phys 129, 363; 1957). Dicke’s tentative theory can be formulated in a way which is compatible with Sciama’s hypothesis on the gravitational constant G. Additionally, such a cosmological model is shown to satisfy Dirac’s second hypothesis on the total number of particles in the universe being proportional to the square of the epoch. In the same context, Dirac’s first hypothesis on an epoch-dependent G -contrary to his predictiondoes not produce a visible time dependence of G which indeed is not observed. While Dicke’s proposal widely describes the classical tests of GR, the cosmological redshift arises from a shortening of measuring rods rather than an expansion of space. The flatness and horizon problems do not arise in the common form.