Rainbow universe

TL;DR

This paper explores rainbow gravity in a cosmological context, deriving modified Friedmann equations that suggest the absence of singularities, and discusses their relation to quantum gravity frameworks like loop quantum cosmology.

Contribution

It introduces an averaged cosmological metric influenced by radiation particles and derives generalized FRW equations, extending previous models and proposing a singularity-free early universe.

Findings

Spacetime curvature has an upper bound, preventing singularities.

Derived modified FRW equations generalize previous solutions.

Discussed analogy with loop quantum cosmology.

Abstract

The formalism of rainbow gravity is studied in a cosmological setting. We consider the very early universe which is radiation dominated. A novel treatment in our paper is to look for an ``averaged'' cosmological metric probed by radiation particles themselves. Taking their cosmological evolution into account, we derive the modified Friedmann-Robertson-Walker(FRW) equations which is a generalization of the solution presented by Magueijo and Smolin. Based on this phenomenological cosmological model we argue that the spacetime curvature has an upper bound such that the cosmological singularity is absent. These modified $FRW$ equations can be treated as effective equations in the semi-classical framework of quantum gravity and its analogy with the one recently proposed in loop quantum cosmology is also discussed.