Large-scale peculiar motions and cosmic acceleration

TL;DR

This paper explores how large-scale peculiar velocities can cause observers to perceive accelerated expansion in a universe that is actually decelerating, challenging standard cosmological interpretations.

Contribution

It demonstrates that linear perturbations in dust-dominated cosmology can lead to apparent acceleration due to peculiar motions, offering a new perspective on cosmic acceleration.

Findings

Observers with peculiar velocities can perceive accelerated expansion.

Large-scale drift motions affect local measurements of the universe's expansion.

Results are consistent with inhomogeneous cosmology studies.

Abstract

Recent surveys seem to support bulk peculiar velocities well in excess of those anticipated by the standard cosmological model. In view of these results, we consider here some of the theoretical implications of large-scale drift motions. We find that observers with small, but finite, peculiar velocities have generally different expansion rates than the smooth Hubble flow. In particular, it is possible for observers with larger than the average volume expansion at their location, to experience apparently accelerated expansion when the universe is actually decelerating. Analogous results have been reported in studies of inhomogeneous (nonlinear) cosmologies and within the context of the Lemaitre-Tolman-Bondi models. Here, they are obtained within the linear regime of a perturbed, dust-dominated Friedmann-Robertson-Walker cosmology.