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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 paper, the authors considered a model of an inhomogeneous universe including a massless scalar field, where the inhomogeneity is assumed to consist of many black holes.
Abstract: We consider a model of an inhomogeneous universe including a massless scalar field, where the inhomogeneity is assumed to consist of many black holes. This model can be constructed by following Lindquist and Wheeler, which has already been investigated without including scalar field to show that an averaged scale factor coincides with that of the Friedmann model. In this work we construct the inhomogeneous universe with an massless scalar field, where we assume that the averaged scale factor and scalar field are given by those of the Friedmann model including a scalar field. All of our calculations are carried out in the framework of Brans-Dicke gravity. In constructing the model of an inhomogeneous universe, we define the mass of a black hole in the Brans-Dicke expanding universe which is equivalent to ADM mass if the mass evolves adiabatically, and obtain an equation relating our mass to the averaged scalar field and scale factor. As the results we find that the mass has an adiabatic time dependence in a sufficiently late stage of the expansion of the universe, and that the time dependence is qualitatively diffenrent according to the sign of the curvature of the universe: the mass increases decelerating in the closed universe case, is constant in the flat case and decreases decelerating in the open case. It is also noted that the mass in the Einstein frame depends on time. Our results that the mass has a time dependence should be retained even in the general scalar-tensor gravitiy with a scalar field potential. Furthermore, we discuss the relation of our results to the uniqueness theorem of black hole spacetime and gravitational memory effect.
Journal ArticleDOI
TL;DR: In this paper, it was shown that there are at least 21 patches out there the same volume as ours, at 95% confidence, even if the precision of our cosmological measurements continues to increase.
Abstract: In the simplest cosmological models consistent with General Relativity, the total volume of the Universe is either finite or infinite, depending on whether or not the spatial curvature is positive. Current data suggest that the curvature is very close to flat, implying that one can place a lower limit on the total volume. In a Universe of finite age, the "particle horizon" defines the patch of the Universe which is observable to us. Based on today's best-fit cosmological parameters it is possible to constrain the number of observable Universe sized patches, N_U. Specifically, using the new WMAP data, we can say that there are at least 21 patches out there the same volume as ours, at 95% confidence. Moreover, even if the precision of our cosmological measurements continues to increase, density perturbations at the particle horizon size limit us to never knowing that there are more than about 10^5 patches out there.
Posted Content
TL;DR: Wang et al. as discussed by the authors explored a cyclic universe by introducing a new chameleon scalar, which is dominant both in the very early universe and in the far future of the universes.
Abstract: Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China(Dated: February 18, 2014)We explore a cyclic universe by introducing a new chameleon scalar field. In the original versionof chameleon scalar field, the mass of the chameleon scalar depends on the environment, specificallyon the ambient matter density. But in this new version, the ambient energy density determines notits mass but its kinetic energy which is achieved by the Lagrange multiplier field. We find the newchameleon scalar is dominant both in the very early universe and in the far future of the universesuch that a cyclic universe is found. In this model of universe, there are infinite cycles of expansionand contraction. Different from the inflationary universe, the corresponding cosmic space-time isgeometrically complete and quantum stable. But similar to the Cyclic Model, the flatness problem,the horizon problem and the large scale structure of the universe can be explained in this cyclicuniverse.
Posted Content
TL;DR: In this paper, the spacetime structure of the spatially uniformly expanding universe is described in terms of a kind of global space and global time instead of the space and time we usually recognize.
Abstract: The spacetime structure of the spatially uniformly expanding universe is described in terms of a kind of global space and global time instead of the space and time we usually recognize. The global space at some instant is a space in which the global time is equal and the global time is equal to the proper time of any point moving together with the expansion of the universe which has elapsed since the big bang. The universe descibed in terms of the global space and time thus defined is open spatially and the Einstein's equations give a solution that the space expands eternally regardless of the mass density of the universe indicating that any expanding universe is open dynamically as well, as it is the case only when the density is less than the critical value in the standard model. In fact the critical density has not any particular meaning in the new frame. Finally the equations for the light path in the new frame are studied and are found similar to those in the standard model.
Journal ArticleDOI
TL;DR: In this paper, a possible scheme of the evolution of the universe was analyzed by studying the bound state energy spectrum in conformal gravity and investigating transitions involving spontaneous changes of the cosmological constant via excitation followed by deexcitation involving particle creation.

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