Scalar- and matter-dominated cosmologies in Schwinger's scalar-tensor theory of gravity

A scalar-tensor theory of gravity, suggested by Schwinger, is reviewed. This theory is like the Brans-Dicke one in that the gravitational constant is time-dependent, and in fact coincides with it whenever the scalar field is weak. It is argued that the apparent discrepancy between the observed mass density of galaxies and the density required by standard cosmologies with $q_0\sim 1$ may be resolved by supposing that we are still in an era in which the scalar field is the dominant source of gravity. Solutions in such an era are discussed, and it is seen that they can be characterized by an increasing gravitational constant. Finally, the more conventional matter-dominated regime is treated.