  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.
