Can a dust dominated universe have accelerated expansion?

Alnes, H.; Amarzguioui, Morad; Grøn, Øyvind

doi:10.1088/1475-7516/2007/01/007

Cited by 32 publications

(32 citation statements)

References 32 publications

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“…Admittedly, those terms are effectively 'small-scale-players'. Now, let us consider Raychaudhuri's equation (see (21) below), restricted to irrotational dust 4 ,…”

Section: Regional Volume Acceleration Despite Local Decelerationmentioning

confidence: 99%

“…which, compared with the corresponding local expression, 4 We assume that the influence of a strong vorticity evolution (that is known to happen on small scales in the nonlinear regime of structure formation) is not relevant on scales larger than the scale of, say, superclusters of galaxies. According to the sign of its appearence in Raychaudhuri's equation, vorticity counteracts gravitation and its effect will be relevant, if averages are performed over domains on and below the scales of galaxy clusters.…”

Section: IImentioning

confidence: 99%

“…Defining the two fundamental forms as in Eqs. (3,4), with the 3-metric coefficients g i j and the extrinsic curvature coefficients K i j := −h µ i h ν j u µ;ν (projected into the hypersurfaces orthogonal to u µ with the help of h µν := g µν +u µ u ν ), Einstein's equations (16) together with (17) (contracted with u ν ) then are equivalent to the following system of equations [7], [178], consisting of the energy or Hamiltonian constraint and the momentum or Codazzi constraints,…”

Section: Einstein's Equations Recalledmentioning

confidence: 99%

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Dark Energy from structure: a status report

2007

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The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein's theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effective volume scale factor, with matter and backreaction source terms. The latter can be represented by an effective scalar field ('morphon field') modeling Dark Energy.The present work provides an overview over the Dark Energy debate in connection with the impact of inhomogeneities, and formulates strategies for a comprehensive quantitative evaluation of backreaction effects both in theoretical and observational cosmology. We recall the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of challenges and unresolved issues in connection with their observational interpretation.The present status of this subject is intermediate: we have a good qualitative understanding of backreaction effects pointing to a global instability of the standard model of cosmology; exact solutions and perturbative results modeling this instability lie in the right sector to explain Dark Energy from inhomogeneities. It is fair to say that, even if backreaction effects turn out to be less important than anticipated by some researchers, the concordance high-precision cosmology, the architecture of current N-body simulations, as well as standard perturbative approaches may all fall short in correctly describing the Late Universe. Keywords

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“…Admittedly, those terms are effectively 'small-scale-players'. Now, let us consider Raychaudhuri's equation (see (21) below), restricted to irrotational dust 4 ,…”

Section: Regional Volume Acceleration Despite Local Decelerationmentioning

confidence: 99%

Section: IImentioning

confidence: 99%

Section: Einstein's Equations Recalledmentioning

confidence: 99%

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Dark Energy from structure: a status report

2007

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“…We wish to remark that the only quantity that is specific to our model is l a , which is explicitly computed for the template metric (24) by integrating Eq. (30). l a is also used in the alternative approach by [63], but their second quantity, R, cannot be used safely since it depends on the behaviour of perturbations [64].…”

Section: Computation Of Observablesmentioning

confidence: 99%

Testing backreaction effects with observations

et al. 2009

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Abstract. In order to quantitatively test the ability of averaged inhomogeneous cosmologies to correctly describe observations of the large scale properties of the Universe, we introduce a smoothed template metric corresponding to a constant spatial curvature model at any time, but with an evolving curvature parameter. This metric is used to compute quantities along an approximate effective lightcone of the averaged model of the Universe. As opposed to the standard Friedmann model, we parameterize this template metric by exact scaling properties of an averaged inhomogeneous cosmology, and we also motivate this form of the metric by results on a geometrical smoothing of inhomogeneous cosmological hypersurfaces. The purpose of the paper is not to demonstrate that the backreaction effect is actually responsible for the Dark Energy phenomenon by explicitly calculating the effect from a local model of the geometry and the distribution of matter, but rather to propose a way to deal with observations in the backreaction context, and to understand what kind of generic properties have to hold in order for a backreaction model to explain the observed features of the Universe on large scales. We test our hypothesis for the template metric against supernova data and the position of the CMB peaks, and infer the goodness-of-fit and parameter uncertainties. We find that averaged inhomogeneous models can reproduce the observations without requiring an additional Dark Energy component (though a volume acceleration is still needed), and that current data do not disfavour our main assumption on the effective lightcone structure. We also show that the experimental uncertainties on the angular diameter distance and the Hubble parameter from Baryon Acoustic Oscillations measurements -forseen in future surveys like the proposed EUCLID satellite project -are sufficiently small to distinguish between a FLRW template geometry and the template geometry with consistently evolving curvature.

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“…[57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72] for some claims and counter-claims. We should however note the possibility that backreaction/averaging effects could be significant, even if they do not lead to acceleration.…”

Section: Dark Energy As a Non-linear Effect From Structurementioning

confidence: 99%

Dark Energy and Dark Gravity

Maartens¹

2007

J. Phys.: Conf. Ser.

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Observations provide increasingly strong evidence that the universe is accelerating. This revolutionary advance in cosmological observations confronts theoretical cosmology with a tremendous challenge, which it has so far failed to meet. Explanations of cosmic acceleration within the framework of general relativity are plagued by difficulties. General relativistic models are nearly all based on a dark energy field with fine-tuned, unnatural properties. There is a great variety of models, but all share one feature in common-an inability to account for the gravitational properties of the vacuum energy. Speculative ideas from string theory may hold some promise, but it is fair to say that no convincing model has yet been proposed. An alternative to dark energy is that gravity itself may behave differently from general relativity on the largest scales, in such a way as to produce acceleration. The alternative approach of modified gravity (or dark gravity) provides a new angle on the problem, but also faces serious difficulties, including in all known cases severe fine-tuning and the problem of explaining why the vacuum energy does not gravitate. The lack of an adequate theoretical framework for the late-time acceleration of the universe represents a deep crisis for theory-but also an exciting challenge for theorists. It seems likely that an entirely new paradigm is required to resolve this crisis.

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Can a dust dominated universe have accelerated expansion?

Cited by 32 publications

References 32 publications

Dark Energy from structure: a status report

Dark Energy from structure: a status report

Testing backreaction effects with observations

Dark Energy and Dark Gravity

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