Conformally Friedmann-Lemaitre-Robertson-Walker cosmologies

TL;DR

This paper explores conformally transformed cosmological models that deviate from standard models without conflicting with cosmic microwave background observations, using cosmographic analysis and observational data to constrain these alternatives.

Contribution

It introduces and analyzes conformally Friedmann-Lemaitre-Robertson-Walker models, providing observational constraints and highlighting their potential as viable alternatives to standard cosmology.

Findings

Conformal models can significantly deviate from standard cosmology without disrupting CMB.

Observational data constrains the conformal mode but still allows a wide range of possibilities.

These models offer a plausible alternative framework for understanding cosmic phenomena.

Abstract

In a universe where, according to the standard cosmological models, some 97% of the total mass-energy is still "missing in action" it behooves us to spend at least a little effort critically assessing and exploring radical alternatives. Among possible, (dare we say plausible), nonstandard but superficially viable models, those spacetimes conformal to the standard Friedmann-Lemaitre-Robertson-Walker class of cosmological models play a very special role --- these models have the unique and important property of permitting large non-perturbative geometric deviations from Friedmann-Lemaitre-Robertson-Walker cosmology without unacceptably distorting the cosmic microwave background. Performing a "cosmographic" analysis, (that is, temporarily setting aside the Einstein equations, since the question of whether or not the Einstein equations are valid on galactic and cosmological scales is essentially the same question as whether or not dark matter/dark energy actually exist), and using both supernova data and information about galactic structure, one can nevertheless place some quite significant observational constraints on any possible conformal mode --- however there is still an extremely rich range of phenomenological possibilities for both cosmologists and astrophysicists to explore.