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Topics: Friedmann-Lemaître-Robertson-Walker Spacetimes

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General Properties * Motivation: They approximate our universe extremely well; The spacetime metric is approximated by an FLRW metric to about 1 part in 104 or better on both large and small scales, except in the immediate vicinity of very strong field objects; Derivatives of the metric are not close to those of FLRW models, so there can be significant differences in the geodesics and curvature, but they do not produce significant backreaction effects on cosmological scales. * Idea: A homogeneous and isotropic metric, characterized by one of three types of 3D constant curvature spatial geometries (open k = −1, flat k = 0, or closed k = 1), and a function a(t) representing its fiducial size at time t; > s.a. geometry of FLRW metrics. * Stability: These solutions are gravitationally unstable to inhomogeneous perturbations, and in the class of averaged inhomogeneous models. @ General references: Hall CQG(00) [projective symmetries]; Camci & Barnes CQG(02)gq/01 [Ricci collineations]; Rindl

Topics: Friedmann-Lemaître-Robertson-Walker Spacetimes Friedmann-Lemaître-Robertson-Walker Spacetimes General Properties * Motivation : They approximate our universe extremely well; The spacetime metric is approximated by an FLRW metric to about 1 part in 10 4 or better on both large and small scales, except in the immediate vicinity of very strong field objects; Derivatives of the metric are not close to those of FLRW models, so there can be significant differences in the geodesics and curvature, but they do not produce significant backreaction effects on cosmological scales. * Id

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