Showing papers on "Particle horizon published in 1977"
TL;DR: In this article, the Friedmann-Robertson-Walker model of the universe is considered, and it is shown that the ultimate phase of perturbation growth is the formation of shock waves.
Abstract: After an introduction on the relativistic vs the Newtonian approach, the Friedmann--Robertson--Walker picture of the Universe is considered: isotropic and homogeneous solution, group-theoretic definition of homogeneity, and Friedmann solution are taken up. The paradox of the infinite gravitational potential in Newtonian theory is disposed of. It has long been believed that gravitational instability is the ultimate cause of matter clustering in the Universe. First, the idealized case of a static universe is treated. Then the Newtonian treatment of small perturbation theory is given for an expanding universe. Recent work concerning the extension of the theory to perturbations of finite amplitude is treated. Simple arguments are given showing that the ultimate phase of perturbation growth is the formation of shock waves. Matter compressed by shock wave forms rather flat clumps. Most of the above is written as examples of formal solutions of hydrodynamic equations with gravitational interaction. Finally, the connection of the theory to observational evidence is established. (RWR)
17 citations
TL;DR: In this article, it was shown that local inhomogeneities with spherical symmetry on a Robertson cosmological universe must be of the ''zero apparent mass'' type, which means that the mean density of each inhomogeneity has to be equal to the cosmology density.
Abstract: We prove that local inhomogeneities: with spherical symmetry: on a Robertson cosmological universe must be of the ''zero apparent mass'' type. It means that the mean density of each inhomogeneity has to be equal to the cosmological density.
6 citations
TL;DR: In this article, it was shown that nonlinear processes involving gravitons in the early universe might have given rise to such a viscosity, which can have important effects in early stages of cosmological models.
3 citations
TL;DR: The manner in which a field of gravitational radiation modifies the cosmological background space-time of the model universe containing it is considered in this article, and a number of examples of the resulting universes are presented in diagrammatic and tabular form.
Abstract: The manner in which a field of gravitational radiation modifies the cosmological background space-time of the model universe containing it is considered. The cosmological equations for the models are solved and a number of examples of the resulting universes are presented in diagrammatic and tabular form.
3 citations
TL;DR: In this paper, the effect of the cosmological constant (Λ) on the expanding tachyon universe has been discussed and the tetrad technique has been used as a mathematical tool for handling the problems of gravitational field equations and perturbation of momentum flux.
Abstract: In the present paper some investigations have been made on the model suggested by Ray for a tachyon dust universe and the results obtained have been compared with the results in the flat Friedmann universe filled with ordinary dust (here called bradyon dust) moving slower than light, by various scientists, on the ground that the role played by time for ordinary matter is played by spatial coordinates for tachyons. The effect of the cosmological constant (Λ) on the expanding tachyon universe also has been discussed here. The tetrad technique has been used as a mathematical tool for handling the problems of gravitational field equations and perturbation of momentum flux.
1 citations
1 citations
TL;DR: In this paper, the effect of fluctuations in the density of matter on the expansion of the universe far from the singularity is analyzed on the basis of a model with a three-dimensional space which is homogeneous and isotropie on the average.
Abstract: The effect of fluctuations in the density of matter on the expansion of the universe far from the singularity is analyzed on the basis of a model with a three-dimensional space which is homogeneous and isotropie on the average. The fluctuations reduce the gravitational effect, retarding the expansion. This effect of the fluctuations increases as the expansion proceeds and can strongly affect the expansion velocity. An equation is derived for the age of the universe on the basis of this model. The age is expressed in terms of observable quantities: the Hubble constant and the acceleration parameter. It is shown that fluctuations lead to an increase in this age. It is concluded that fluctuations must be taken into account in studying the expansion of the observable universe.