  Beginning with a geometric motivation for dark matter going back to the
axioms of general relativity, we show how scalar field dark matter, which
naturally forms dark matter density waves due to its wave nature, may cause the
observed barred spiral pattern density waves in many disk galaxies and triaxial
shapes with plausible brightness profiles in many elliptical galaxies. If
correct, this would provide a unified explanation for spirals and bars in
spiral galaxies and for the brightness profiles of elliptical galaxies. We
compare the results of preliminary computer simulations with photos of actual
galaxies.
