The Dark Side of the Universe
Neta Bahcall (Princeton University)
What is the Universe made of? Recent observations suggest surprising new
results: not only most of the matter in the Universe is dark and
unconventional but, more surprisingly, the major component of the Universe
may be in the form of 'dark energy' -- a form of energy that opposes the
pull of gravity and causes the expansion of the universe to accelerate. By
combining recent observations of clusters of galaxies, distant supernovae,
and the cosmic microwave background, we find evidence for a Universe that
has only 5% 'normal' matter, 20% dark matter, and 75% 'dark energy'. The
observations suggest a Universe that is lightweight, with only 25% of the
critical mass-density needed to halt the Universal expansion, and a
geometry that is flat with no space curvature. The observations of the dark
side of the Universe and their implications will be discussed.
