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Particle horizon

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


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TL;DR: In this article, the energy-momentum conservation of a spherically symmetric perturbation in linear approximation on a FRW cosmological background is investigated in the de Donder gauge.
Abstract: Density perturbations are considered during the radiation-dominated and the dust-dominated periods of the expanding universe. The perturbations are taken to have spherical symmetry and the investigation is carried out in the de Donder gauge. In order to guarantee the energy-momentum conservation of the perturbation in the de Donder gauge a compatibility condition is obtained. Equations for the propagation of a spherically symmetric perturbation in linear approximation on a FRW cosmological background are presented. It turns out that the evolutiontendency of the formation is mainly predicted by the state of the cosmic background. A radiation-dominated universe does not stimulate growth processes; the perturbation will be in a frozen state or it will diffuse. It is found that the dust-dominated universe stimulates the perturbation mass to grow. The rate of this cosmic affected growing process is proportional toR−1 (R being the scale factor of the universe), so that it seems that almost all galaxies were formed at the beginning of the present dust-dominated era.

2 citations

Journal ArticleDOI
TL;DR: In this paper, it is suggested that gravity may not be asymptotically free at short distances because of the interaction of the graviton with matter, and the possibility of abnormally strong gravity at high energies or short distances is discussed in some detail.
Abstract: It is suggested that gravity may not be asymptotically free at short distances because of the interaction of the graviton with matter. If gravity indeed becomes strong at high energies, a revolutionary change of our present theory on the early universe would seem to be necessary. During the first extremely small fraction of a second in the big-bang universe, gravity would have been so strong that it might not have been described by Einstein's theory of general relativity. The possibility of abnormally strong gravity at high energies or short distances is discussed in some detail. A possible explanation is proposed for the nonvanishing mean baryon number density of the universe. It is also pointed out that the universe may well escape from the catastrophic singularity of Penrose and Hawking.

2 citations

Posted Content
TL;DR: In this article, the authors considered the water phase transition between the gas and liquid phases, which takes place at 100 degrees Celsius as the temperature of the gaseous water cools down.
Abstract: Modern mathematical cosmology is based heavily on the Hawking-Penrose singularity theorem [1] which states that once collapse approaches a certain point, evolution to a singularity is unavoidable. Here the singularity denotes something similar to a shrinking point beyond which extending the spacetime is unattainable. The singularity theorem indicates that there was a singularity at the beginning of our universe which is believed to have expanded now. In the standard cosmology, the expansion of the universe from a single point, namely Big Bang is assumed to have occurred at this singularity. We now consider phase transition which is assumed to have happened in the evolution of the universe around 75,000 years after the Big Bang. Before going into details of the phase transition in cosmology, we consider the water phase transition between the gas and liquid phases, which takes place at 100 degrees Celsius as the temperature of the gaseous water cools down. When either above or below the critical temperature the water is either gas or liquid, and at the critical temperature water is in a gas-liquid mixture form. It is known that in the universe there exist two types of particles: massive particles such as electrons and massless ones such as photons, namely quanta of light. In obtaining the Hawking-Penrose singularity theorem, they have exploited the so-called strong energy condition. Assuming that the early universe was filled with a perfect fluid consisting of massive particles and/or massless particles and using the strong energy condition, one could find equations of state for each particle.

2 citations

Journal ArticleDOI
TL;DR: In this paper, the energy density of massless particles generated during the cosmological expansion is calculated in the lowest-order perturbation theory and the general structure of conformai anomalies of the energy-momentum tensor is established.
Abstract: The general structure of conformai anomalies of the energy-momentum tensor is established. The energy density of massless particles generated during the cosmological expansion is calculated in the lowest-order perturbation theory. Estimates are made that indicate that the energy density of generated massless particles in the early universe can significantly exceed the energy density of the generated massive particles.

2 citations

Posted Content
TL;DR: In this paper, the generalized Dyer-Roeder equation for the angular diameter distance of the inhomogeneous universe is derived and solved for different cosmological models, which are crucial ingredients in galaxy number counts and gravitational lenses.
Abstract: We study the large-scale inhomogeneity of the Universe based on the averaging procedure of Buchert and Ehlers. The generalized Dyer-Roeder equation for the angular diameter distance of the inhomogeneous Universe is derived and solved for different cosmological models. We make a comparison of certain cosmic observables, such as the Hubble function, angular diameter distance,cosmological correction factor of homogeneous and inhomogeneous cosmological models, which are crucial ingredients in galaxy number counts and gravitational lenses.

2 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202320
202247
20216
202010
201910
201814