  Stars account for only about 0.5% of the content of the Universe; the bulk of
the Universe is optically dark. The dark side of the Universe is comprised of:
at least 0.1% light neutrinos; 3.5% +/- 1% baryons; 29% +/- 4% cold dark
matter; and 66% +/- 6% dark energy. Now that we have characterized the dark
side of the Universe, the challenge is to understand it. The critical questions
are: (1) What form do the dark baryons take? (2) What is (are) the
constituent(s) of the cold dark matter? (3) What is the nature of the
mysterious dark energy that is causing the Universe to speed up.
