Scale Invariance at low accelerations (aka MOND) and the dynamical anomalies in the Universe

Understand

Galactic systems, and the Universe at large, exhibit large dynamical anomalies: The observed matter in them falls very short of providing enough gravity to account for their dynamics.

• The mainstream response to this conundrum is to invoke large quantities of `dark matter' -- which purportedly supplies the needed extra gravity -- and also of `dark energy', to account for further anomalies in cosmology, such as the observed, accelerated expansion.
• The MOND paradigm offers a different solution: a breakdown of standard dynamics (gravity and/or inertia) in the limit of low accelerations -- below some acceleration $a_0$.
• In this limit, dynamics become space-time scale invariant, and is controlled by a gravitational constant $\mathcal{A}_0\equiv Ga_0$, which replaces Newton's $G$.