Coordinate Confusion in Conformal Cosmology

TL;DR

This paper argues that conformal coordinate transformations do not remove superluminal recession velocities in FLRW cosmologies, reaffirming that the expansion of space remains a valid concept in general relativity.

Contribution

It demonstrates that conformal transformations cannot eliminate superluminal expansion velocities in open or flat matter-only FLRW cosmologies, supporting the validity of space expansion.

Findings

Conformal transformations do not remove superluminal recession velocities.

All open or flat matter-only FLRW cosmologies exhibit superluminal expansion.

The concept of space expansion remains valid in general relativity.

Abstract

A straight-forward interpretation of standard Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmologies is that objects move apart due to the expansion of space, and that sufficiently distant galaxies must be receding at velocities exceeding the speed of light. Recently, however, it has been suggested that a simple transformation into conformal coordinates can remove superluminal recession velocities, and hence the concept of the expansion of space should be abandoned. This work demonstrates that such conformal transformations do not eliminate superluminal recession velocities for open or flat matter-only FRLW cosmologies, and all possess superluminal expansion. Hence, the attack on the concept of the expansion of space based on this is poorly founded. This work concludes by emphasizing that the expansion of space is perfectly valid in the general relativistic framework, however, asking the question of whether space really expands is a futile exercise.