Is the Universe Simpler than LCDM?
  In the standard cosmological model, the Universe consists mainly of two
invisible substances: vacuum energy with constant mass-density
rho_v=\Lambda/(8pi G) (where Lambda is a `cosmological constant' originally
proposed by Einstein and G is Newton's gravitational constant) and cold dark
matter (CDM) with mass density that is currently rho_{DM,0}\sim 0.3 rho_v. This
`LCDM' model has the virtue of simplicity, enabling straightforward calculation
of the formation and evolution of cosmic structure against the backdrop of
cosmic expansion. Here we review apparent discrepancies with observations on
small galactic scales, which LCDM must attribute to complexity in the baryon
physics of galaxy formation. Yet galaxies exhibit structural scaling relations
that evoke simplicity, presenting a clear challenge for formation models. In
particular, tracers of gravitational potentials dominated by dark matter show a
correlation between orbital size, R, and velocity, V, that can be expressed
most simply as a characteristic acceleration, a_{DM}\sim 1 km^2 s^{-2} pc^{-1}
\approx 3 x 10^{-9} cm s^{-2} \approx 0.2c\sqrt{G rho_v}, perhaps motivating
efforts to find a link between localized and global manifestations of the
Universe's dark components.
