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Friedmann–Lemaître–Robertson–Walker metric

About: Friedmann–Lemaître–Robertson–Walker metric is a research topic. Over the lifetime, 4113 publications have been published within this topic receiving 87752 citations. The topic is also known as: FLRW metric.


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Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of the presence of opaque objects on the optical properties of small-scale cosmological observations by propagating one hundred thousand null geodesics through space-times, with matter arranged in either compact opaque objects or diffuse transparent haloes.
Abstract: On small scales the observable Universe is highly inhomogeneous, with galaxies and clusters forming a complex web of voids and filaments. The optical properties of such configurations can be quite different from the perfectly smooth Friedmann-Lemaitre-Robertson-Walker (FLRW) solutions that are frequently used in cosmology, and must be well understood if we are to make precise inferences about fundamental physics from cosmological observations. We investigate this problem by calculating redshifts and luminosity distances within a class of cosmological models that are constructed explicitly in order to allow for large density contrasts on small scales. Our study of optics is then achieved by propagating one hundred thousand null geodesics through such space-times, with matter arranged in either compact opaque objects or diffuse transparent haloes. We find that in the absence of opaque objects, the mean of our ray tracing results faithfully reproduces the expectations from FLRW cosmology. When opaque objects with sizes similar to those of galactic bulges are introduced, however, we find that the mean of distance measures can be shifted up from FLRW predictions by as much as $10\%$. This bias is due to the viable photon trajectories being restricted by the presence of the opaque objects, which means that they cannot probe the regions of space-time with the highest curvature. It corresponds to a positive bias of order $10\%$ in the estimation of $\Omega_{\Lambda}$ and highlights the important consequences that astronomical selection effects can have on cosmological observables.

25 citations

Journal ArticleDOI
01 Jun 1981-Nature
TL;DR: In this article, it has been shown that primordial isothermal perturbations are incompatible with the standard Friedman-Robertson-Walker (FRW) universe for baryosynthesis.
Abstract: In the gravitational instability theory, the present structure in the Universe is envisaged to have evolved from small initial inhomogeneities which are of two generic types: isothermal and adiabatic. It has been shown that in the grand unified theory (GUT) for baryosynthesis primordial isothermal perturbations are incompatible with the standard Friedman–Robertson–Walker (FRW) universe. Here we discuss four non-standard models in which the two are compatible. Of these models two prove to be viable: (1) a universe which is initially dominated by large-scale inhomogeneous shear and (2) a universe which undergoes a de Sitter phase during the GUT phase transition. We also show how to deduce new constraints on chaotic behaviour near the cosmological singularity.

24 citations

Journal ArticleDOI
TL;DR: Barotropic FRW cosmologies with dissipative features acting on the scale factors and spatial curvature of the universe were presented in this paper, where a coupling parameter denoted by K between the two classes of solutions was introduced.
Abstract: Barotropic FRW cosmologies are presented from the standpoint of nonrelativistic supersymmetry. First, we reduce the barotropic FRW system of differential equations to simple harmonic oscillator differential equations. Employing the factorization procedure, the solutions of the latter equations are divided into the two classes of bosonic (nonsingular) and fermionic (singular) cosmological solutions. We next introduce a coupling parameter denoted by K between the two classes of solutions and obtain barotropic cosmologies with dissipative features acting on the scale factors and spatial curvature of the universe. The K-extended FRW equations in comoving time are presented in explicit form in the low coupling regime. The standard barotropic FRW cosmologies correspond to the dissipationless limit K = 0.

24 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss the relationship of Tod's conjecture to an earlier one of Goode and Wainwright (1985), and reduce the proof of this conjecture to establishing uniqueness of solution to an appropriate initial value problem.
Abstract: According to Penrose's Weyl tensor hypothesis (1979), an appropriate boundary condition to impose at any initial singularity is that the Weyl tensor should vanish there. Cosmological models that admit isotropic singularities provide a mathematical framework for studying this hypothesis. Tod (1957) has conjectured that, within the isotropic singularity framework, the only models that satisfy the Penrose boundary condition are the exact FRW models. The author discusses the relationship of this conjecture to an earlier one of Goode and Wainwright (1985), and reduces the proof of Tod's conjecture to establishing uniqueness of solution to an appropriate initial value problem.

24 citations

Journal ArticleDOI
TL;DR: In this article, the authors present solutions of cosmological perturbations for an ideal-fluid medium with a constant pressure (p) to density (μ) relation in a flat Friedmann-Lemaitre-Robertson-Walker (FLRW) background model.
Abstract: We present solutions of cosmological perturbations for an ideal-fluid medium with a constant pressure (p) to density (μ) relation in a flat Friedmann-Lemaitre-Robertson-Walker (FLRW) background model. Solutions are presented for six different gauge choices which include most of those conventionally used. Both exact and asymptotic solutions are shown in tabular forms. Solutions span a range in w(≡p/μ) from -1 to 1. On subhorizon scales except for the uniform-density gauge, for general w, the density perturbations in all gauge choices behave in the same way; also for a pressureless medium the behavior is in accord with the Newtonian results

24 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023150
2022352
2021196
2020204
2019214
2018191