Local and non-local measures of acceleration in cosmology

Abstract

Current cosmological observations, when interpreted within the framework of a homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) model, strongly suggest that the Universe is entering a period of accelerating expansion. This is often taken to mean that the expansion of space itself is accelerating. In a general spacetime, however, this is not necessarily true. We attempt to clarify this point by considering a handful of local and non-local measures of acceleration in a variety of inhomogeneous cosmological models. Each of the chosen measures corresponds to a theoretical or observational procedure that has previously been used to study acceleration in cosmology, and all measures reduce to the same quantity in the limit of exact spatial homogeneity and isotropy. In statistically homogeneous and isotropic spacetimes, we find that the acceleration inferred from observations of the distance-redshift relation is closely related to the acceleration of the spatially averaged universe, but does not necessarily bear any resemblance to the average of the local acceleration of spacetime itself. For inhomogeneous spacetimes that do not display statistical homogeneity and isotropy, however, we find little correlation between acceleration inferred from observations and the acceleration of the averaged spacetime. This shows that observations made in an inhomogeneous universe can imply acceleration without the existence of dark energy.

19 pages, 10 figures. Several references added or amended, some minor clarifications made in the text

References in corpus (24)

• Confronting Lemaitre-Tolman-Bondi models with Observational Cosmology
• Accelerated expansion from structure formation
• A new framework for analyzing the effects of small scale inhomogeneities in cosmology
• CMB anisotropies seen by an off-center observer in a spherically symmetric inhomogeneous universe
• Living in a Void: Testing the Copernican Principle with Distant Supernovae
• Looking the void in the eyes - the kSZ effect in LTB models
• Testing the Void against Cosmological data: fitting CMB, BAO, SN and H0
• Precision cosmology defeats void models for acceleration
• Szekeres Swiss-Cheese model and supernova observations
• Can inhomogeneties accelerate the cosmic volume expansion?
• The Possibility of Cosmic Acceleration via Spatial Averaging in Lemaitre-Tolman-Bondi Models
• Luminosity distance in "Swiss cheese" cosmology with randomized voids: I. Single void size
• The Cosmic Microwave Background in an Inhomogeneous Universe - why void models of dark energy are only weakly constrained by the CMB
• Applicability of the linearly perturbed FRW metric and Newtonian cosmology
• Reconciling the local void with the CMB
• Pressure gradients, shell crossing singularities and acoustic oscillations - application to inhomogeneous cosmological models
• Apparent and average acceleration of the Universe
• Description of our cosmological spacetime as a perturbed conformal Newtonian metric and implications for the backreaction proposal for the accelerating universe
• Cosmological acceleration from structure formation
• LTB universes as alternatives to dark energy: does positive averaged acceleration imply positive cosmic acceleration?
• Averaging Robertson-Walker Cosmologies
• Toward a No-Go Theorem for an Accelerating Universe through a Nonlinear Backreaction
• Structure Formation, Backreaction and Weak Gravitational Fields
• A New Type of Exact Arbitrarily Inhomogeneous Cosmology: Evolution of Deceleration in the Flat Homogeneous-On-Average Case

Cited by in corpus (10)

• Another look at redshift drift and the backreaction conjecture
• Does small scale structure significantly affect cosmological dynamics?
• Backreaction and FRW consistency conditions
• Cosmic backreaction and the mean redshift drift from symbolic regression
• The effect of dark matter discreteness on light propagation
• cp3-bench: A tool for benchmarking symbolic regression algorithms tested with cosmology
• Expansion and Growth of Structure Observables in a Macroscopic Gravity Averaged Universe
• Hubble Diagrams in Statistically Homogeneous, Anisotropic Universes
• Evaluating backreaction with the ellipsoidal collapse model
• Can we remove the systematic error due to isotropic inhomogeneities?