Comment on "Turnaround in Cyclic Cosmology"

TL;DR

This paper critiques a cyclic universe model by Baum and Frampton, arguing that their proposed deflation mechanism is invalid because the Hubble length becomes infinite at the turnaround, challenging the model's entropy resolution.

Contribution

It provides a critical analysis showing the invalidity of the deflation mechanism in the cyclic universe model due to the Hubble length behavior.

Findings

Hubble length becomes infinite at the turnaround

Deflation mechanism is not valid in this model

Challenges the entropy resolution in cyclic cosmology

Abstract

We comment on a recent paper by L. Baum and P. H. Frampton [Phys. Rev. Lett. 98, 071301 (2007)] where it was argued that the entropy problem can be resolved in a peculiar cyclic universe model through a deflation mechanism (i.e., the universe is fragmented into many disconnected causal patches at the turnaround). We point out that in this cyclic model the Hubble length will become infinity at the turnaround, thus the deflation scenario is not valid.