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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 authors consider a cosmology in which a spherically symmetric large scale inhomogeneous enhancement or a void are described by an inhomogenous metric and Einstein's gravitational equations.
Abstract: We consider a cosmology in which a spherically symmetric large scale inhomogeneous enhancement or a void are described by an inhomogeneous metric and Einstein's gravitational equations. For a flat matter dominated universe the inhomogeneous equations lead to luminosity distance and Hubble constant formulae that depend on the location of the observer. For a general inhomogeneous solution, it is possible for the deceleration parameter to differ significantly from the FLRW result. The deceleration parameter q0 can be interpreted as q0 > 0 in a FLRW universe (q0 = 1/2 for a flat matter dominated universe) and q0 < 0 as inferred from the inhomogeneous enhancement that is embedded in a FLRW universe. A spatial volume averaging of local regions in the backward light cone has to be performed for the inhomogeneous solution at late times to decide whether the decelerating parameter q can be negative for a positive energy condition. The CMB temperature fluctuations across the sky can be unevenly distributed in the northern and southern hemispheres in the inhomogeneous matter dominated solution, in agreement with the analysis of the WMAP power spectrum data by several authors. The model can possibly explain the anomalous alignment of the quadrupole and octopole moments observed in the WMAP data.
102 citations
TL;DR: This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry.
Abstract: While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura formalism of numerical relativity in synchronous gauge. This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry. The universe that emerges exhibits an average Friedmann-Lemaitre-Robertson-Walker (FLRW) behavior; however, this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background.
101 citations
TL;DR: In this paper, a cosmological model with a pressureless fluid with a constant bulk viscosity was proposed as an explanation for the present accelerated expansion of the universe, and all the possible scenarios for the universe predicted by the model according to their past, present and future evolution were classified.
Abstract: We test a cosmological model which the only component is a pressureless fluid with a constant bulk viscosity as an explanation for the present accelerated expansion of the universe. We classify all the possible scenarios for the universe predicted by the model according to their past, present and future evolution and we test its viability performing a Bayesian statistical analysis using the SCP ``Union'' data set (307 SNe Ia), imposing the second law of thermodynamics on the dimensionless constant bulk viscous coefficient and comparing the predicted age of the universe by the model with the constraints coming from the oldest globular clusters. The best estimated values found for and the Hubble constant H0 are: = 1.922±0.089 and H0 = 69.62±0.59 (km/s)Mpc−1 with a χ2min = 314 (χ2d.o.f = 1.031). The age of the universe is found to be 14.95±0.42 Gyr. We see that the estimated value of H0 as well as of χ2d.o.f are very similar to those obtained from ΛCDM model using the same SNe Ia data set. The estimated age of the universe is in agreement with the constraints coming from the oldest globular clusters. Moreover, the estimated value of is positive in agreement with the second law of thermodynamics (SLT). On the other hand, we perform different forms of marginalization over the parameter H0 in order to study the sensibility of the results to the way how H0 is marginalized. We found that it is almost negligible the dependence between the best estimated values of the free parameters of this model and the way how H0 is marginalized in the present work. Therefore, this simple model might be a viable candidate to explain the present acceleration in the expansion of the universe.
101 citations
TL;DR: It is demonstrated that the recently discovered large-scale structure of the Universe (voids and filaments) can be explained by cosmic strings and the presence of pointlike structures (''knobs'') of masses >10/sup 7/M/sub cirdot/ in the vicinity of larger galaxies is predicted.
Abstract: We wish to demonstrate that the recently discovered large-scale structure of the Universe (voids and filaments) can be explained by cosmic strings. We also predict the presence of pointlike structures (''knobs'') of masses >10/sup 7/M/sub cirdot/ in the vicinity of larger galaxies. The present analysis is limited to order-of-magnitude estimates. A detailed analysis would necessarily have to go into the full nonlinear theory of the growth of fluctuations in the Universe.
101 citations
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TL;DR: In this article, the authors compare two forms of the Robertson-Walker (RW) metric, written in (the traditional) comoving coordinates, and a set of observer-dependent coordinates, first for the well known de Sitter universe containing only dark energy, and then for a newly derived form of the RW metric, for a universe with dark energy and matter.
Abstract: The cosmological principle, promoting the view that the universe is homogeneous and isotropic, is embodied within the mathematical structure of the Robertson-Walker (RW) metric. The equations derived from an application of this metric to the Einstein Field Equations describe the expansion of the universe in terms of comoving coordinates, from which physical distances may be derived using a time-dependent expansion factor. These coordinates, however, do not explicitly reveal properties of the cosmic spacetime manifested in Birkhoff's theorem and its corollary. In this paper, we compare two forms of the metric--written in (the traditional) comoving coordinates, and a set of observer-dependent coordinates--first for the well-known de Sitter universe containing only dark energy, and then for a newly derived form of the RW metric, for a universe with dark energy and matter. We show that Rindler's event horizon--evident in the co-moving system--coincides with what one might call the "curvature horizon" appearing in the observer-dependent frame. The advantage of this dual prescription of the cosmic spacetime is that with the latest WMAP results, we now have a much better determination of the universe's mass-energy content, which permits us to calculate this curvature with unprecedented accuracy. We use it here to demonstrate that our observations have probed the limit beyond which the cosmic curvature prevents any signal from having ever reached us. In the case of de Sitter, where the mass-energy density is a constant, this limit is fixed for all time. For a universe with a changing density, this horizon expands until de Sitter is reached asymptotically, and then it too ceases to change.
99 citations