Comment on "Shear-free barotropic perfect fluids cannot rotate and expand simultaneously" by R. Goswami and G.F.R. Ellis

TL;DR

This paper critiques a recent study on shear-free barotropic perfect fluids, highlighting an error and emphasizing that the question of their rotation and expansion remains unresolved.

Contribution

It identifies an error in Goswami and Ellis's work and clarifies that the problem of simultaneous rotation and expansion in these fluids is still open.

Findings

Identified an error in the previous paper by Goswami and Ellis.

Confirmed that the question of rotation and expansion in shear-free barotropic fluids remains unresolved.

Highlights the need for further research on this topic.

Abstract

We point out an error in a recent paper by Goswami and Ellis. As a consequence the question of whether shear-free barotropic perfect fluids (with $p+\mu\neq 0$) can or cannot rotate and expand simultaneously, is still wide open