Two exotic elements have been introduced into the standard
cosmological model: non-baryonic dark matter and dark energy. The success
in converting a hypothesis into a solid theory depends strongly on whether
we are able to solve the problems in explaining observations with these
dark elements and whether the solutions of these problems are unique within
the standard paradigm without recourse to alternative scenarios. We have
not achieved that success yet because of numerous inconsistencies, mainly
on galactic scales, the non-detection so far of candidate particles for
dark matter, and the existence of many alternative hypotheses that might
substitute the standard picture to explain the cosmological observations. A
review of some ideas and facts is given here.
(arXiv:1808.09823)