Showing papers on "Friedmann–Lemaître–Robertson–Walker metric published in 1987"
54 citations
TL;DR: In this article, the condition of isotropy of pressure in the case of Bianchi I space-time filled with a perfect fluid was shown to reduce via a suitable scale transformation to a linear second-order differential equation, which admits as particular solutions those of Friedmann, Robertson, and Walker.
Abstract: We show that the condition of isotropy of pressure in the case of Bianchi I space-time filled with a perfect fluid reduces via a suitable scale transformation to a linear second-order differential equation, which admits as particular solutions those of Friedmann, Robertson, and Walker. These particular solutions are then used for generating many new local rotational symmetry Bianchi I solutions. Some of their physical properties are then studied.
27 citations
TL;DR: In this article, the self-creation theory of gravitation is solved for a vacuum with the aid of a space-time metric of Friedmann, and some physical properties of the solution are discussed.
Abstract: The field equations of the self-creation theory of gravitation proposed by Barber are solved for a vacuum with the aid of a space-time metric of Friedmann. Some physical properties of the solution are discussed.
25 citations
15 citations
12 citations
TL;DR: In this article, a new solution of Einstein's field equations is found, which describes a dust-filled Kantowski-Sachs universe with a positive cosmological constant, where the mass density of the dust is positive.
8 citations
TL;DR: The uniqueness of the Friedmann-Robertson-Walker (FRW) cosmological models was established in this paper. But the uniqueness of FRW cosmologies was not discussed in this paper.
Abstract: By accepting the validity of certain conjectures in classical general relativity and kinetic theory, it is argued that, in a sense, the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) cosmological models are unique. This is accomplished in two steps. First, there is reason to believe that kinetic theory requires perfect fluids to be shear-free. Second, it seems that general relativity constrains expanding shear-free fluids to be irrotational. The uniqueness of the FRW models then follows, since it has already been established that they are the only space-times which represent an expanding shear-free irrotational perfect fluid that are physically reasonable on a global scale.
6 citations
TL;DR: In this article, exact solutions for radiation-filled cosmological differential equations of Brans-Dicke theory with the assumption that the radius of curvatureQ of the universe varies directly as thenth power of time were obtained.
Abstract: Considering a Robertson-Walker line element, exact solutions are obtained for radiation-filled cosmological differential equations of Brans-Dicke theory with the assumption that the radius of curvatureQ of the universe varies directly as thenth power of time. The solution is found to be valid for closed space only and the coupling constantw of the scalar tensor theory is necessarily negative. The radius of curvature of increases linearly with respect to the age of the universe, while the gravitational constantk varies directly as the square of the radius of the universe. The solution obtained is in contradiction to Dirac's hypothesis, in which the gravitational constant should decrease with time in an expanding universe.
4 citations
TL;DR: In this paper, the analytic form of the geodesics in the Robertson-Walker metric is found for all possible Friedmann models (closed, flat and open) and the solutions of the Einstein equations for the above models and for the equations of state corresponding to dust and radiation.
Abstract: The analytic form of the geodesics in the Robertson-Walker metric is found. All kinds of geodesics (timelike, null and spacelike) are examined, and for all possible Friedmann models (closed, flat and open). Use is made of the solutions of the Einstein equations for the above models and for the equations of state corresponding to dust and radiation. The cosmological constant is taken equal to zero.
4 citations
Journal Article•
2 citations
TL;DR: In this article, a generalization of the characterization of inflation is given, and various ways in which a positive cosmological term in the Einstein equations may induce inflation are discussed for spatially homogeneous, anisotropic models.
Abstract: A generalization of the characterization of inflation is given. On its basis, the various ways in which a positive cosmological term in the Einstein equations may induce inflation is discussed for spatially homogeneous, anisotropic models.
TL;DR: In this paper, the exterior field of the Robertson-Walker metric in the Lyttleton-Bondi universe with cosmological constant was considered and it was shown that the exterior solution of this universe is simply the empty space-time of general relativity.
Abstract: The exterior field of the Robertson-Walker metric in the Lyttleton-Bondi universe with cosmological constant is considered. It is shown that in the presence of cosmological constant, the exterior solution of this Universe is simply the empty space-time of general relativity.
01 Apr 1987
TL;DR: By numerically integrating the field equations in a radiation and matter dominated models, the instability of a static, infinitely long and straight vacuum string solution under inhomogeneous axisymmetric time-dependent perturbations is investigated and oscillatory solutions are discovered.
Abstract: We investigate the stability of a static, infinitely long and straight vacuum string solution under inhomogeneous axisymmetric time-dependent perturbations. We find it to be perturbatively stable. We further extend our work by finding a string solutions in an expanding Universe. The back reaction of the string on the gravitational field has been ignored. The background is assumed to be a Friedman-Robertson-Walker (FRW) cosmology. By numerically integrating the field equations in a radiation and matter dominated models, we discover oscillatory solutions. The possible damping of these oscillations is discussed. For late times the solution becomes identical to the static one studied in the first part of the paper. 19 refs., 8 figs.
01 Jan 1987
TL;DR: In this paper, it was shown that the universe need not be of the Friedman-Robertson-Walker (FRW) type in order to satisfy the observational constraints and that the anthropic principle is not sufficient.
Abstract: The standard picture of the Universe is of a system highly Isotropic and spatially homogeneous on scales larger than the observed clustering scale of local luminous matter. Evidence for this is derived from the isotropy of the microwave background radiation and the abundance of helium. In this picture the Universe is represented by a Friedman-Robertson-Walker (FRW) model with small perturbations. However, while exact homogeneity and isotropy imply a FRW model, observations of approximate homogeneity and isotropy in a finite region do not, as we shall see, imply approximate FRW behaviour for all time even locally. We therefore find that the universe need not be of FRW type in order to satisfy the observational constraints. This has important consequences for proposed explanations of approximate homogeneity and isotropy. Such explanations have been focussed on (i) the choice of initial conditions; (ii) dynamical dissipation of anisotropy and imhomogeneity and (iii) the anthropic principle. Under (i) I shall discuss the role of gravitational entropy and I shall mention Mach’s Principle. (Quantum initial conditions are considered by Hartle in this volume.) I shall also comment on the anthropic explanation. Investigations of the behaviour of certain cosmological models of non-FRW type suggest that these approaches are unlikely to be successful.
TL;DR: In this paper, it was shown that the k = 0 FRW metric admits a dust solution in the Brans-Dicke (BD) theory, also admits and imperfect fluid distribution along with an electromagnetic field.
Abstract: It is shown that thek=0 FRW metric which admits a dust solution in the Brans-Dicke (BD) theory, also admits and imperfect fluid distribution along with an electromagnetic field. The solutions are functions of time and radial coordinates and they satisfy all necessary energy and thermodynamic conditions.