Most controversies in contemporary cosmology concern modifications
of LCDM designed to resolve tensions like that between distance-ladder
and inverse-distance-ladder values of H0. The proposed modifications are
generally “small” like making the vacuum energy density time-dependent
(e.g. quintessence) or adding extra light degrees of freedom (e.g. neutrinos).
Here we will discuss more radical “Far From LCDM” (FFLCDM) models.
Such models either deny that the observed cosmological acceleration is caused
by dark energy (e.g. backreaction models) or deny that the
data implies acceleration (e.g. Colin et al. arXiv:1808.04597).
Physical models that prevent the expected deceleration
have also been proposed (e.g. Dirac-Milne models arXiv:1804.03067).
We will discuss the strategies that the FFLCDM models have used to
avoid the standard empirical and theoretical constraints.
DPhP