  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 $G$. With the new dynamics, the various detailed
manifestations of the anomalies in galaxies are predicted with no need for dark
matter. The cosmological anomalies could, but need not have to do with small
accelerations. For example, the need for dark matter in accounting for the
expansion history of the Universe is eliminated if the relevant gravitational
constant is $\approx 2\pi G$. Such a `renormalization' of $G$ could be a
dimensionless parameter of a MOND theory. The constant $a_0$ turns out to carry
cosmological connotations, in that $2\pi a_0\approx cH_0\approx
c^2(\Lambda/3)^{1/2}$, where $H_0$ is the present expansion rate of the
Universe, and $\Lambda$ the measured `cosmological constant'. There are MOND
theories in which this `coincidence' is natural. I draw on enlightening
historical and conceptual analogies from quantum theory to limelight aspects of
MOND. I also explain how MOND may have strong connections with effects of the
quantum vacuum on local dynamics.
