Cosmological models and their observational validation

Davidson, W. ; Narlikar, J. V. (1966) Cosmological models and their observational validation Reports on Progress in Physics, 29 (2). pp. 539-622. ISSN 0034-4885

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The observational data of cosmology are presented in considerable detail and their interpretation in terms of various cosmological models is described. The data survey the nature and cosmic distribution of luminous matter (galaxies), radio sources, quasars, intergalactic matter, the radio and optical background radiation, x rays, γ rays and cosmic rays. The theoretical basis of cosmological models is described in its general aspects and in particular cases. Topics discussed include the homogeneous anisotropic models, isotropic models, Mach's principle, relativistic cosmology, Newtonian cosmology and the various versions of the steady-state theory and creation of matter. Theoretical observable relations are derived or described for the isotropic models of relativistic cosmology and the steady-state theory. The theoretical relations between observables are compared with the data from various observational tests. These include the red-shift-apparent-magnitude relation, counts of radio sources, the radiation background at radio and optical frequencies and the x-ray and γ-ray background. The possibility of intergalactic cosmic rays is discussed and an account is given of recent observational tests for intergalactic hydrogen. The relevance to particular cosmologies of neutrino degeneracy, the absorber theory of radiation, the age distribution of galaxies and the origin of the chemical elements is analysed in some detail. The most important conclusion is that several tests, among them the measurements of red shift and apparent magnitude, the counts of radio sources, the radio background at high frequency and the present He/H abundance ratio, all support a universe that was denser in the past. Furthermore, recent tests suggest that the density of hydrogen in intergalactic space is below the mean density of luminous matter (galaxies) by several orders of magnitude. Thus the evidence is now extremely strong against the steady-state cosmology in its original simple form, while relativistic cosmology to the above extent finds support. On the other hand, there is the difficulty that the evolutionary ages of some star clusters are estimated to exceed the predicted ages of galaxies in both cosmologies, while the absorber theory of radiation gives consistent retarded solutions in the steady-state theory but not in relativistic cosmology. Although contrary arguments exist, there is strong theoretical evidence that a singularity in the relativistic cosmology is inevitable, and no way has yet been found in conventional physics either to prevent it or to describe it. However, the discovery of new force fields in physics at high density, on the lines of the negative energy C field of the steady-state theory, may show how a contracting universe may be reversed into expansion without singularity. This might imply a finitely oscillating universe, for which there are special difficulties. The theoretical and observational study of the recently discovered quasars may throw light on this issue. But from the point of view of present-day physics the evidence points to a fundamental singularity of the observable Universe that occurred about ten thousand million years ago. There is also considerable evidence that this was followed by a hyperbolic expansion.

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