  The concept of exotic charged dust is introduced here to represent dark
matter. The term "exotic" means that the dust is not composed of normal matter,
and the charge--for lack of a better term--is not an electric charge. It is
also shown that the often-used approximate expression for dark matter density
corresponds to an exact solution of the coupled Einstein-Maxwell equations for
charged dust. The Einstein field equations tells us is that for a flat universe
the cosmological constant acts as a gravitating negative energy distribution
that is gravitationally repulsive; following Schwinger, it is shown that the
vacuum must have a negative energy spectrum if QFT is to be gauge invariant.
