Towards the geometry of the Universe from data

Abstract

We present a new algorithm that can reconstruct the full distributions of metric components within the class of spherically symmetric dust universes that may include a cosmological constant. The algorithm is capable of confronting this class of solutions with arbitrary data and opens a new observational window to determine the value of the cosmological constant. In this work we use luminosity and age data to constrain the geometry of the universe up to a redshift of z = 1.75. We show that, although current data are perfectly compatible with homogeneous models of the universe, simple radially inhomogeneous void models that are sometimes used as alternative explanations for the apparent acceleration of the late time universe cannot yet be ruled out.In doing so we reconstruct the density of cold dark matter out to z = 1.75 and derive constraints on the metric components when the universe was 10.5 Gyr old within a comoving volume of approximately 1 Gpc 3 .

Inhomogeneous cosmology and backreaction: Current status and future prospects

“…The works are still being developed with the aim of putting tighter constraints on the spacetime geometry. 82,83 A less ambitious alternative of the program (but nonetheless also very important) is rather than constraining the metric of our Universe from the data, to use the data to directly test fundamental assumptions of the standard cosmological model, which is based on the spatially homogeneous and isotropic FLRW geometry. One way is to study the distribution of galaxies.…”

Geodesic-light-cone coordinates and the Bianchi I spacetime

“…Such a method was used in refs. [7,8] to directly reconstruct spacetime's metric from observations. More specifically, the GLC coordinates were first exploited to perform lightcone averages in a perturbed Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime, in order to determine the effect of inhomogeneities on the distance-redshift relation [9][10][11], and therefore on the interpretation of the Hubble diagram [12][13][14]; GLC coordinates were also recently applied to gravitational lensing in general [15,16], to galaxy number counts [17], and to the propagation of ultrarelativistic particles [18].…”

Numerically reconstructing the geometry of the Universe from data

“…The observational cosmology programme [1] aims to reconstruct the background geometry (equivalently the cosmological metric) directly from observations. Here we give a brief overview of a newly proposed algorithm [2] that solves this problem for the class of spherically symmetric dust universes that may include a cosmological constant (henceforth ΛLTB models, see [3] for example). The algorithm employs a non-parametric approach in which Gaussian process priors are used to fix the free functions of the model.…”