Relativistic numerical cosmology with silent universes

Bolejko, Krzysztof

doi:10.1088/1361-6382/aa9d32

Cited by 38 publications

(47 citation statements)

References 98 publications

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“…Conjecture 2 (the cosmological gravitational entropy conjecture) together with Proposition 1 seem to be in contradiction with Conjecture 1 (the cosmological no-hair conjecture), which postulates that a universe with a positive cosmological constant will end up as a homogeneous and isotropic de Sitter model. In this Section we will test these conjectures using the Simsilun simulation [35].…”

Section: Resultsmentioning

confidence: 99%

“…The Simsilun simulation is based on the code simsilun 1 . The description of the code, equations, and its applications are described in the 'Methods Paper' [35]. The Methods Paper describes how one can use the Millennium simulation [36,37,38] to set up the initial conditions for the code simsilun.…”

Section: The Simsilun Simulationmentioning

confidence: 99%

“…In addition, the virialisation mechanism no 1 is implemented, whose technical details are is described in Sec. 3 in the Methods Paper [35]. The Millennium Simulation is based on the ΛCDM model with Ω M = 0.25, Ω Λ = 0.75, and H 0 = 73.0 km s −1 Mpc −1 .…”

Section: The Simsilun Simulationmentioning

confidence: 99%

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Gravitational entropy and the cosmological no-hair conjecture

Bolejko

2018

Phys. Rev. D

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The gravitational entropy and no-hair conjectures seems to predict contradictory future states of our Universe. The growth of the gravitational entropy is associated with the growth of inhomogeneity, while the no-hair conjecture argues that a universe dominated by dark energy should asymptotically approach a homogeneous and isotropic de Sitter state. The aim of this paper is to study these two conjectures. The investigation is based on the Simsilun simulation, which simulates the universe using the approximation of the Silent Universe. The Silent Universe is a solution to the Einstein equations that assumes irrotational, non-viscous, and insulated dust, with vanishing magnetic part of the Weyl curvature. The initial conditions for the Simsilun simulation are sourced from the Millennium simulation, which results with a realistically appearing but relativistic at origin simulation of a universe. The Simsilun simulation is evolved from the early universe (t = 25 Myr) till far future (t = 1000 Gyr). The results of this investigation show that both conjectures are correct. On global scales, a universe with a positive cosmological constant and non-positive spatial curvature does indeed approach the de Sitter state. At the same time it keeps generating the gravitational entropy. *

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Section: Resultsmentioning

confidence: 99%

Section: The Simsilun Simulationmentioning

confidence: 99%

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Gravitational entropy and the cosmological no-hair conjecture

Bolejko

2018

Phys. Rev. D

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“…In order to improve distance estimates from measured redshifts, approaches have been developed to refine the assumption of a spatially homogeneous matter density distribution, among others, see Dyer & Roeder (1972), Dyer & Roeder (1973), Bonvin et al (2006), Bolejko et al (2011), or Bolejko (2018. Most importantly, for the degeneracies arising in the gravitational lensing formalism, Bolejko (2011) showed that the distance-redshift relation as defined by Equation (6) holds for spatially homogeneous universes and is a good approximation with negligible corrections for universes in which density perturbations along a line of sight average out.…”

Section: Distances and H0 In The Cosmic Backgroundmentioning

confidence: 99%

Generalised model-independent characterisation of strong gravitational lenses – VI. The origin of the formalism intrinsic degeneracies and their influence on H0

Wagner

2019

Monthly Notices of the Royal Astronomical Society

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We give a physical interpretation of the formalism intrinsic degeneracies of the gravitational lensing formalism that we derived on a mathematical basis in part IV of this series. We find that all degeneracies occur due to the partition of the mass density along the line of sight. Usually, it is partitioned into a background (cosmic) density and a foreground deflecting object. The latter can be further partitioned into a main deflecting object and perturbers. Weak deflecting objects along the line of sight are also added, either to the deflecting object or as a correction of the angular diameter distances, perturbing the cosmological background density. A priori, this is an arbitrary choice of reference frame and partition. They can be redefined without changing the lensing observables which are sensitive to the integrated deflecting mass density along the entire line of sight. Reformulating the time delay equation such that this interpretation of the degeneracies becomes easily visible, we note that the source can be eliminated from this formulation, which simplifies reconstructions of the deflecting mass distribution or the inference of the Hubble constant, H 0 . Subsequently, we list necessary conditions to break the formalism intrinsic degeneracies and discuss ways to break them by model choices or including non-lensing observables like velocity dispersions along the line of sight with their advantages and disadvantages. We conclude with a systematic summary of all formalism intrinsic degeneracies and possibilities to break them.

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“…A comparison of such backreaction effects with observations has been undertaken in [9]. Furthermore numerical solutions of Einstein's equations for a Silent Universe show "that the spatial curvature emerges due to nonlinear evolution of cosmic structures" [10].…”

Section: Introductionmentioning

confidence: 99%

Analytical solutions for two inhomogeneous cosmological models with energy flow and dynamical curvature

Stichel

2018

Phys. Rev. D

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Recently we have introduced a nonrelativistic cosmological model (NRCM) exhibiting a dynamical spatial curvature. For this model the present day cosmic acceleration is not attributed to a negative pressure (dark energy) but it is driven by a nontrivial energy flow leading to a negative spatial curvature. In this paper we generalize the NRCM in two different ways to the relativistic regime and present analytical solutions of the corresponding Einstein equations. These relativistic models are characterized by two inequivalent extensions of the FLWR metric with a time-dependent curvature function K(t) and an expansion scalar a(t). The fluid flow is supposed to be geodesic. The model V1 is shear-free with isotropic pressure and therefore conformal flat. It shows some common properties with the spherically symmetric Stephani models but it exhibits also some specific differences. In contrast to V1 the second model V2 shows a nontrivial shear and an anisotropic pressure. For both models the inhomogeneous solutions of the corresponding Einstein equations will agree in leading order at small distances with the NRCM if a(t) and K(t) are each identical with those determined in the NCRM. This will be achieved by the demand of vanishing isotropic pressure and its first derivative w.r.t. r 2 at the coordinate origin r = 0. Then the metric is completely fixed by three constants. The arising energy momentum tensor contains a nontrivial energy flow vector. Our models violate locally the weak energy condition. As this may be caused by some averaging we speculate about to view each of our models as a local average of some other more fundamental model. Global volume averaging leads to explicit expressions for the effective scale factor and the expansion rate H(z). Backreaction effects cancel each other for the model V2 but they are nonzero and proportional to the square of the magnitude of the energy flow for the model V1. The large scale (relativistic) corrections to the NCRM results are small for the model V2 for a small-sized energy flow. We have reproduced a corresponding adjustment of the three free constants from [1] to cosmic chronometer data leading to the prediction of an almost constant, negative value for the dimensionless curvature function k(z) ∼ −1 for redshifts z < 2.

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Relativistic numerical cosmology with silent universes

Cited by 38 publications

References 98 publications

Gravitational entropy and the cosmological no-hair conjecture

Gravitational entropy and the cosmological no-hair conjecture

Generalised model-independent characterisation of strong gravitational lenses – VI. The origin of the formalism intrinsic degeneracies and their influence on H0

Analytical solutions for two inhomogeneous cosmological models with energy flow and dynamical curvature

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