From galactic bars to the Hubble tension $-$ weighing up the
  astrophysical evidence for Milgromian gravity
  Astronomical observations reveal a major deficiency in our understanding of
physics $-$ the detectable mass is insufficient to explain the observed motions
in a huge variety of systems given our current understanding of gravity,
Einstein's General theory of Relativity (GR). This missing gravity problem may
indicate a breakdown of GR at low accelerations, as postulated by Milgromian
dynamics (MOND). We review the MOND theory and its consequences, including in a
cosmological context where we advocate a hybrid approach involving light
sterile neutrinos to address MOND's cluster-scale issues. We then test the
novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy
clusters, and the large scale structure of the Universe. We also consider
whether the standard cosmological paradigm ($\Lambda$CDM) can explain the
observations, and review several previously published highly significant
falsifications of it. Our overall assessment considers both the extent to which
the data agree with each theory and how much flexibility each has when
accommodating the data, with the gold standard being a clear a priori
prediction not informed by the data in question. We also consider some future
tests, including on scales much smaller than galaxies. Our conclusion is that
MOND is favoured by a wealth of data across a huge range of astrophysical
scales, ranging from the kpc scales of galactic bars to the Gpc scale of the
local supervoid and the Hubble tension, which is alleviated in MOND through
enhanced cosmic variance.
