Newtonian Fractional-Dimension Gravity and MOND
  This paper introduces a possible alternative model of gravity based on the
theory of fractional-dimension spaces and its applications to Newtonian
gravity. In particular, Gauss's law for gravity as well as other fundamental
classical laws are extended to a $D$-dimensional metric space, where $D$ can be
a non-integer dimension.
  We show a possible connection between this Newtonian Fractional-Dimension
Gravity (NFDG) and Modified Newtonian Dynamics (MOND), a leading alternative
gravity model which accounts for the observed properties of galaxies and other
astrophysical structures without requiring the dark matter hypothesis. The MOND
acceleration constant $a_{0} \simeq 1.2 \times 10^{ -10}\mbox{m}\thinspace
\mbox{s}^{ -2}$ can be related to a natural scale length $l_{0}$ in NFDG, i.e.,
$a_{0} \approx GM/l_{0}^{2}$, for astrophysical structures of mass $M$, and the
deep-MOND regime is present in regions of space where the dimension is reduced
to $D \approx 2$.
  For several fundamental spherically-symmetric structures, we compare MOND
results, such as the empirical Radial Acceleration Relation (RAR), circular
speed plots, and logarithmic plots of the observed radial acceleration
$g_{obs}$ vs. the baryonic radial acceleration $g_{bar}$, with NFDG results. We
show that our model is capable of reproducing these results using a variable
local dimension $D\left (w\right )$, where $w =r/l_{0}$ is a dimensionless
radial coordinate. At the moment, we are unable to derive explicitly this
dimension function $D\left (w\right )$ from first principles, but it can be
obtained empirically in each case from the general RAR.
  Additional work on the subject, including studies of axially-symmetric
structures, detailed galactic rotation curves fitting, and a possible
relativistic extension, will be needed to establish NFDG as a viable
alternative model of gravity.
