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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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Journal ArticleDOI
TL;DR: In this article, the authors investigated higher dimensional cosmological models in the semiclassical approximation with Hartle-Hawking Boundary conditions, assuming a gravitational action which is described by the scalar curvature with a cosmology constant.
Abstract: We investigate higher dimensional cosmological models in the semiclassical approximation with Hartle-Hawking Boundary conditions, assuming a gravitational action which is described by the scalar curvature with a cosmological constant. In the framework the probability for quantum creation of an inflationary universe with a pair of black holes in a multidimensional universe is evaluated. The probability for creation of a universe with a spatial section with $S^{1}XS^{D -2}$ topology is then compared with that of a higher dimensional de Sitter universe with $S^{D -1}$ spatial topology. It is found that a higher dimensional universe with a product space with primordial black holes pair is less probable to nucleate when the extra dimensions scale factors do not vary in an inflating universe.

5 citations

Journal ArticleDOI
TL;DR: In this paper, a simple perturbation description unique for all signs of curvature, and based on the gauge-invariant formalisms, is proposed to demonstrate that density perturbations propagate in the flat radiation-dominated universe in exactly the same way as electromagnetic or gravitational waves propagated in the epoch of the matter domination.
Abstract: A simple perturbation description unique for all signs of curvature, and based on the gauge-invariant formalisms is proposed to demonstrate that: (1) The density perturbations propagate in the flat radiation-dominated universe in exactly the same way as electromagnetic or gravitational waves propagate in the epoch of the matter domination. (2) In the open universe, sounds are dispersed by curvature. The space curvature defines the minimal frequency $\omega_{\rm c}$ below which the propagation of perturbations is forbidden. Gaussian acoustic fields are considered and the curvature imprint in the perturbations spectrum is discussed.

5 citations

Journal ArticleDOI
02 Nov 2016
TL;DR: In this paper, the authors considered regional space expansion along with regional space contraction, one dynamic process being the complement of the other, and exploited the dual dynamic nature of the medium to construct a nonexpanding cellular model of the universe.
Abstract: The conventional view is that the cosmic spectral-redshift, an effect observed in all directions of the heavens, is primarily a measure of space-medium expansion. Significantly, the more distant the galaxy the greater is the redshift — and the greater is the intervening space expansion. The redshift evidence is unequivocal; its implication, its interpretation, however, is not. The important question is this: Does all the evidence for “space” expansion necessarily imply that the whole visible universe must also be expanding? Given a universe whose volume consists mostly of expanding space, does it follow that the entire universe must expand? On this momentous issue rests the future course of cosmology. Yet, it seems, the question has never been seriously addressed. Meanwhile, there is a growing awareness that the assertion of whole-universe expansion is a non-sequitur fallacy. Universe expansion is the unscientific extrapolation of space expansion. It is an unwarranted extrapolation of general relativity. Instead of universal expansion, this paper considers regional space expansion along with regional space contraction — one dynamic process being the complement of the other. This dual dynamic nature of the medium is given full recognition and exploited in the construction of a nonexpanding cellular model of the Universe. The emphasis is on the cell structure and the two “space” postulates involved in sustaining the structure, for it is in the structure of the cosmic cells that the nature of the relationship between Lambda and gravity is revealed.

5 citations

Posted Content
TL;DR: In this paper, the massless scalar field vacuum is considered to accelerate the expansion of the universe and it is found that the vacuum tends to decelerate an expansion of universe if the conformal acceleration of universe is equal to zero.
Abstract: Back-reaction of the massless scalar field vacuum to the Universe expansion is considered. Automatic renormalization procedure based on the equations of motion instead of the Friedman equation is used to avoid the cosmological constant problem. It is found, that the vacuum tends to decelerate an expansion of Universe if the conformal acceleration of Universe is equal to zero. In contract, the vacuum acts as the true cosmological constant in Universe expanding with the present day acceleration. Estimation for third derivative of the Universe scale factor with respect to conformal time is presented.

5 citations

Journal ArticleDOI
Paul S. Henry1
29 Feb 1980-Science
TL;DR: An intuitive model for the expansion of the universe is developed in which special relativity is used to describe events seen by a hypothetical observer in a Lorentz frame of reference, which approximates an open universe with increasing accuracy as time evolves.
Abstract: An intuitive model for the expansion of the universe is developed in which special relativity is used to describe events seen by a hypothetical observer in a Lorentz frame of reference. The cosmic microwave background photons he sees are the red-shifted remnants of hot photons emitted from the matter flying rapidly away from him. This special relativistic model, also called the Milne model, represents the extreme case of a Friedmann (general relativistic) universe in the limit of vanishingly small density of matter. The special relativistic model approximates an open universe (one that expands forever) with increasing accuracy as time evolves.

5 citations


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