scispace - formally typeset
Search or ask a question
Topic

Particle horizon

About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.


Papers
More filters
Dissertation
01 Jan 1988
TL;DR: In this article, the authors consider the formation of black holes in the early universe and consider the effect of a large cosmological constant (vacuum energy term) on the behaviour of a spherically symmetric anisotropic universe, characterised by different expansion rates in the radial and transverse directions.
Abstract: The Universe today is observed to be extremely homogeneous and isotropic on large scales. The dipole anisotropy of the microwave background, due to the relative motion of the Earth, is measured to be less than one part in 10 4. The quadropole component, due to intrinsic anisotropies, is even smaller. Thus, any viable mathematical or physical description of the large scale properties of the Universe must encompass the observational evidence and reflect this large degree of uniformity. The most popular, and certainly the most successful, description of the Universe at the present epoch is provided by the Friedmann-Robertson-Walker (FRW) cosmological models. These spherically symmetric models consider the Universe as an isotropic, spatially homogeneous, perfect fluid matter distribution, which is in a state of dynamic evolution. All of the FRW cosmologies exhibit an expansion, i. e. the volume of the spatial sections varies with time, during some stage of their evolution, in agreement with the observed expansion of the Universe. An important consequence of this behaviour is that it leads to a singularity at a finite time in the past when the volume of the spatial sections becomes zero and matter becomes infinitely dense and infinitely hot (the hot Big Bang scenario). The isotropy and homogeneity of the Universe at the present epoch, cannot necessarily be extrapolated back to these earlier times. Certainly, there must exist inhomogeneities on small scales at all epochs in order to produce the observed structure, such as galaxies, clusters and superclusters. This raises the question of the effect of anisotropy on the initial stages of the evolution of the Universe. In this thesis we consider cosmological models which differ significantly from the FRW descriptions. We consider the effect of a large cosmological constant (vacuum energy term) on the behaviour of a spherically symmetric anisotropic universe, characterised by different expansion rates in the radial and transverse directions. The analysis is simplified considerably by imposing the condition that the model admits a self-similar symmetry. The techniques of similarity and dimensional analysis are employed to obtain a class of spatially inhomogeneous solutions to the Einstein field equations with a non-zero cosmological term. These solutions are found to contain some which tend asymptotically to a de-Sitter FRW solution and thereby extend the cosmological "no-hair" theorems, which state that under certain restrictions any model containing a large positive cosmological term will evolve to a de-Sitter cosmology at late times. Such models are attractive since they tend to isotropic spacetimes. Similarity methods are also applied to the study of an anisotropic spacetime with an imperfect fluid as source. The fluid description of the cosmology is chosen to include the dissipative processes of shear and bulk viscosity but to neglect the effects due to the existence of magnetic fields, heat conduction or acceleration along the flow lines. In order to obtain a self-similar description of such a fluid we must impose certain conditions on the form of the viscous coefficients of bulk and shear. This allows a degree of tractability but restricts the physical significance of the models. Solutions are found for which the matter distribution acts as (i) a 'presureless fluid' with an equation of state given by T11=0 and (ii) a 'stiff' fluid with equation of state, T1 1=-T0 0. The conditions under which the Universe may attain either of these extreme properties are discussed in relation to the physical processes occurring in the matter distribution at different epochs. It is found that the presence of viscosity has a marked effect on the dynamics of the Universe, particularly at early times. The self-similar viscous models with a stiff equation of state are then considered with respect to the formation of black holes in the early Universe. The difficulties of obtaining a smooth continuation of the viscous solutions from the Universe particle horizon to a black hole event horizon are discussed in view of the limitations encountered in the non-viscous black hole solutions. Finally, the possibility of future investigations inspired by the considerations of this thesis are discussed. In particular, the determination of a geometric symmetry corresponding to self-symmetry of the second kind and the formation of a self-consistent similarity treatment of imperfect fluid cosmologies are deemed important. Possible lines of research to these ends are considered.

1 citations

Posted Content
TL;DR: In this article, the authors present a Static Universe in a generalized Brans-Dicke gravity theory, where the coupling "constant" varies with time, as well as the scalar field.
Abstract: We present a Static Universe in a generalized Brans-Dicke gravity theory, where the coupling “constant ” varies with time, as well as the scalar field. There is amplificatiom of gravitational waves in such Universe, at least when it is “young”. PACS 98.80-Hw

1 citations

Journal ArticleDOI
TL;DR: In this article, a rigorous solution of the field equations with a finite density of matter in the universe is obtained in the context of classical gravitation theory, where the density of mass is a function of the number of particles in the entire universe.
Abstract: A rigorous solution of the field equations with a finite density of matter in the Universe is obtained in the context of classical gravitation theory.

1 citations

01 Jan 2011
TL;DR: In this article, it was shown that a weaker ZPE in earlier times had the ability to account for some otherwise inexplicable astronomical phenomena, such as the formation of the solar system.
Abstract: Plasma physics has recently opened up new vistas in astronomy based on the interaction of electric and magnetic fields in contrast to gravitational interactions. Yet the magnitude of these electric and magnetic interactions is dependent upon the strength of the Zero Point Energy (ZPE) which controls the properties of the vacuum. The evidence indicates that the ZPE strength has increased with time. This has had the effect of reducing the voltages, current strengths and speed of plasma interactions as time increased. Research indicates that a weaker ZPE in earlier times had the ability to account for some otherwise inexplicable astronomical phenomena. In particular, it gives a new understanding of the role played by electro-magnetic processes earlier in the history of our solar system. Several examples are discussed.

1 citations

Journal ArticleDOI
TL;DR: In this article, the evolution of the gravitational instability on the background of an oscillating, homogeneous, and isotropic universe in the relativistic theory of gravitation considering a massive graviton is described.
Abstract: We have solved the general equations derived in Part I [1] to describe the evolution of the gravitational instability on the background of an oscillating, homogeneous, and isotropic universe in the relativistic theory of gravitation considering a massive graviton. Complete solutions, along with their short-wave and long-wave asymptotics, are given for most distinctive stages of the evolution of the universe, namely, near the turning points corresponding to the maximum and minimum densities, as well as in the radiation-dominated, nonrelativistic, and quintessence stages. In all these cases, except for the turning points, the gauge vectors have been determined for the scalar and vector perturbations, allowing the elimination of wave solutions with a phase velocity that is equal to the speed of light. We conclude that, in principle, the observed structure of the universe could have been formed during a sufficiently large number of its cycles.

1 citations


Network Information
Related Topics (5)
Black hole
40.9K papers, 1.5M citations
88% related
Dark matter
41.5K papers, 1.5M citations
86% related
Gauge theory
38.7K papers, 1.2M citations
85% related
Neutrino
45.9K papers, 1M citations
84% related
Supersymmetry
29.7K papers, 1.1M citations
83% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202320
202247
20216
202010
201910
201814