Particle creation and Dirac's large numbers hypothesis

Reference is made to cosmologies based on Dirac's large numbers hypothesis (Nature 139:323 (1937) and Proc. Roy. Soc. A333:403 (1973)). Dirac suggested that continuous creation of matter is required. Two modes of particle creation have been proposed and cosmological models corresponding to each mode have been studied. It is here shown that, within the context of the large numbers hypothesis, the number of particles in the Universe varies as expected (N proportional to t2) so that particle creation is unnecessary. Some undesirable features of cosmologies based on the large numbers hypothesis are also discussed. In order to appreciate fully the results presented for cosmologies based on the large numbers hypothesis a review is made of the corresponding relationship in conventional cosmologies in which the gravitational constant G does not vary with time. It is found, amongst other things that there is no nucleosynthesis in cosmologies based on the large numbers hypothesis, making the large and uniform abundance of He inexplicable. Another undesirable finding with the large numbers hypothesis is the extremely steep decline in the number of particles in the Universe with increasing temperature. Yet another undesirable finding concerns the scattering of photons by electrons in the early Universe; there is no way to establish thermodynamic equilibrium between the photons and electrons, and the black body spectrum of the background radiation is without explanation. (U.K.)