Showing papers on "Particle horizon published in 1978"

The Whirl Theory of the Origin of Structure in the Universe

Abstract: There are at least two reasons for examining different theories of galaxy formation: (i) We do not know the initial conditions in the early Universe; (ii) We do not know which forces were most important for the origin and evolution of initial perturbations. The first reason forces us to deal with perturbations of different types, i.e. adiabatic, turbulent and entropy perturbations. The second makes it necessary to examine the influence of non-gravitational forces — for instance, local vortices. The whirl theory of the formation of stroduces — by means of initial conditions — non-potential vortex perturbations.

Long-wavelength perturbations of a Friedmann universe, and anisotropy of the microwave background radiation

Abstract: Observational evidence, which is necessarily confined to a region of the universe limited in space (within the observer's horizon), implies a high degree of homogeneity and isotropy for the large-scale structure of the universe. In principle, substantial deviations of the properties of the real universe from the parameters of an idealized Friedmann cosmological model could have prevailed on scales exceeding that of the horizon. Constraints on the amplitude of perturbations with such long wavelengths are imposed by the virtual isotropy (deltaT/T<10/sup -4/) of the observed background radiation. This information on deltaT/T together with the natural hypothesis that the perturbations are statistically independent implies that on spatial scales exceeding the horizon there exist no significant (with amplitude of order greater than deltaT/T) perturbations in density. For certain types of perturbations in the metric (in the gravitational field), the amplitude could be appreciable without contradicting the empirical limits on deltaT/T.

On the origin of Hawking mini black-holes and the cold early Universe

Abstract: A simple argument is outlined leading to the result that the mass of mini black holes exploding today is 10 to the 15th power g. A mathematical model is discussed which indicates that the equation of state is greatly softened in the high-density regime and a phase transition may exist, such that any length (particularly very small sizes) will grow with time irrespective of its relation to the size of the particle horizon. It is shown that the effect of spin-2 mesons with respect to the equation of state is to soften the pressure and make it negative. An analytical expression is given for the probability that any particular region in a hot early universe will evolve into a black hole.

Gravitational Waves in a Bianchi Type I Universe

Abstract: Tensor perturbation equations in a diagonal Bianchi type-I universe are derived in a preliminary study of the propagation of gravitational waves in anisotropic universes. Exact solutions to these equations are obtained for an axisymmetric Kasner background, in which wave propagation is along the symmetry axis. Near the singularity the universe behaves like a generalized Kasner solution and at large time like it possesses a directed stream of radiation with energy density equal to pressure. It is shown to be equivalent to thee linear limit of the Einstein-Rosen or Gowdy T/sup 3/ solution. The back reaction of gravitational waves on a type-I universe with matter is also studied in the long- and short-wavelength limits. High-frequency waves with sufficient energy could reverse the contracting axis of the universe into expansion, while waves propagating in all directions could bring about isotropization of the background. Long-wavelength perturbations act like an effective anisotropy potential which induces ''small oscillations'' on the background. The universe with such long waves can be shown to be equivalent to the weak-field limit of a ''corner run'' solution in the type-IX and type-VII/sub 0/ universes.

Is the universe expanding

Abstract: It is shown that spherically symmetric static general relativistic cosmological space-times can reproduce the same cosmological observations as the currently favored Friedmann-Robertson-Walker universes, if the usual assumptions are made about the local physical laws determining the behavior of matter, provided that the universe is inhomogeneous and our galaxy is situated close to one of its centers. Only (i) unverifiable a priori assumptions, (ii) detailed physical and astrophysical arguments, or (iii) observation of the time variation of cosmological quantities can lead us to conclude that the universe we live in is not such a static space-time.

Exact cosmological solution with particle creation in JBD theory

Abstract: Exact solutions are sought by taking the generated particles of spin 1/2 (according to the creation rate of Schafer and Dehnen [1]) as matter sources of the Cosmological equations of JBD theory. There exists one exact solution for which the “gravitational constant” decreases linearly with time and the mass of the universe increases proportionally to the square of its age (Dirac's hypotheses). The radius of curvature increases linearly with time while the density decreases inversely with it. It is found that for an age of the universe ≃ 10−22 sec only two particles have populated the universe. This is assumed to be the initial state of the model. The calculated present particle number and their density are in agreement with the observed data. This model implies that all present matter (excluding the two initial particles) has been created by the expansion of the universe.

The steady state universe revisited, with stochastic electrodynamics as a guide

Abstract: The steady state universe is considered in the light of stochastic electrodynamics. It is shown that the cosmic background radiation and the continuous creation of matter are rather well accounted for. Several other topics, such as the anomalous redshifts and the diffuse gamma-ray background, are considered, with interesting results.

On the Creation of Scalar Particles in Some Anisotropic Universe

Abstract: Because of an importance of the particle creation (especially, its possible fulfilment of the black-body law with a definite temperature) in an early universe to various other cosmological problems, we study how the creation of scalar particles occurs in the Bianchi­ type I anisotropic universe adopted in our previous works on the quantized scalar field. It is shown that, as in a special isotropic case dealt with in recent papers, the creation may occur at the sacrifice of the requirement that the quantization procedure should reproduce the usual theory for a free field in the limit when the anisotropic universe changes into the Minkowski space-time. It is further shown that the creation occurs in accordance with the black-body law only in a 2-dimensional hyper-surface relating to the anisotropic cosmic expansion, provided that we fix two arbitrary constants appearing in a general expression for the Feynman propagator in terms of a procedure similar to that in the isotropic case. A speculation on the isotropization of our model-universe is also made from the standpoint of seeking the attainment of the thermal equilibrium in the whole universe.

The isotropy of the universe on scales exceeding the horizon

Abstract: I would like to describe in a few words work which was done by Zeldovich and myself. It gives some restrictions on the amplitude of possible very large-scale density fluctuations mentioned by Peebles. the main question investigated in this work is the following. What can be said, using known observational data and some general hypotheses, about structure of the Universe beyond the region accessible for observation at the present epoch? in fact we consider density fluctuations (as well as rotational perturbations and gravitational waves) with wavelengths larger than the horizon. We use the observational fact that the quadrupole-type anisotropy of the microwave background radiation is absent at the level of δT/T −4 . It is interesting to know if it may happen that, at the present epoch, there exists a significant density of perturbations (say, with the dimensionless amplitude of the order of 10 −1 ) which we do not even suspect because the corresponding wavelength is very long and therefore direct observation of the entire perturbation is not possible. Such a direct observation will be possible only in the remote future when the horizon becomes equal to the corresponding wavelength. To answer the question we make a natural but very important assumption. Namely, we assume that the harmonic perturbations of different wavelengths are not correlated in any particular way. Otherwise, they might fit together in such a way that all perturbations (and, therefore, δT/T) would be especially small within the horizon while significant perturbations could take place just beyond the horizon. A situation of this kind would imply that an observer at the Earth occupies a unique position in the Universe. We assume, on the contrary, that all observers are equivalent. All of them, even causally unconnected observers, could detect similar restrictions on the anisotropy of the microwave background, δT/T −4 . Nevertheless, the question still exists whether small perturbations unnoticeable by every observer within his horizon can represent different parts of a significant long wavelength limit. the main result of this investigation can be formulated in the following way. the observational data on δT/T in combination with the natural hypothesis on the statistical independence of different harmonics leads to the conclusion that in the Universe there are no significant (i.e. with the amplitude exceeding δT/T) density fluctuations on any spatial scale larger than the horizon. (The paper will be published in Astr. Zh. U. S. S. R. j November-December, 1977.