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Astronomical observations reveal a major deficiency in our understanding ofphysics $-$ the detectable mass is insufficient to explain the observed motionsin a huge variety of systems given our current understanding of gravity,Einstein's General theory of Relativity (GR). This missing gravity problem mayindicate a breakdown of GR at low accelerations, as postulated by Milgromiandynamics (MOND). We review the MOND theory and its consequences, including in acosmological context where we advocate a hybrid approach involving lightsterile neutrinos to address MOND's cluster-scale issues. We then test thenovel predictions of MOND using evidence from galaxies, galaxy groups, galaxyclusters, and the large-scale structure of the Universe. We also considerwhether the standard cosmological paradigm ($\Lambda$CDM) can explain theobservations and review several previously published highly significantfalsifications of it. Our overall assessment considers both the extent to whichthe data agree with each theory and how much flexibility each has whenaccommodating the data, with the gold standard being a clear $a~priori$prediction not informed by the data in question. Our conclusion is that MOND isfavoured 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 localsupervoid and the Hubble tension, which is alleviated in MOND through enhancedcosmic variance. We also consider several future tests, mostly on scales muchsmaller than galaxies.

From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity