On the determination of dark energy

Abstract

I consider some of the issues we face in trying to understand dark energy. Huge fluctuations in the unknown dark energy equation of state can be hidden in distance data, so I argue that model-independent tests which signal if the cosmological constant is wrong are valuable. These can be constructed to remove degeneracies with the cosmological parameters. Gravitational effects can play an important role. Even small inhomogeneity clouds our ability to say something definite about dark energy. I discuss how the averaging problem confuses our potential understanding of dark energy by considering the backreaction from density perturbations to second-order in the concordance model: this effect leads to at least a 10% increase in the dynamical value of the deceleration parameter, and could be significantly higher. Large Hubble-scale inhomogeneity has not been investigated in detail, and could conceivably be the cause of apparent cosmic acceleration. I discuss void models which defy the Copernican principle in our Hubble patch, and describe how we can potentially rule out these models.

12 pages, 7 figures

References in corpus (6)

• Average observational quantities in the timescape cosmology
• A (giant) void is not mandatory to explain away dark energy with a Lemaitre - Tolman model
• The influence of structure formation on the cosmic expansion
• Phenomenology of the Invisible Universe
• Non-parametric Dark Energy Degeneracies
• The Accelerated Expansion of the Universe Challenged by an Effect of the Inhomogeneities. A Review

Cited by in corpus (8)

• Does the growth of structure affect our dynamical models of the universe? The averaging, backreaction and fitting problems in cosmology
• Establishing homogeneity of the universe in the shadow of dark energy
• Using H(z) data as a probe of the concordance model
• Null tests of the cosmological constant using supernovae
• Light propagation in statistically homogeneous and isotropic universes with general matter content
• Applicability of the linearly perturbed FRW metric and Newtonian cosmology
• Is backreaction really small within concordance cosmology?
• Observational Constraints on the Averaged Universe