Supernovae, Dark Energy, and the Accelerating Universe -- What Next?


Saul Perlmutter
Supernova Cosmology Project
Lawrence Berkeley National Laboratory


The supernova research groups were surprised to discover that
the expansion of the universe is not decelerating (as expected due
to gravity), but accelerating.  Apparently, some new, unidentified
"dark energy" that pervades all space is accelerating the expansion.
This is the first decade in which we can begin to address such
fundamental physics questions with a variety of measurement
techniques.  We have been using Type Ia supernovae to track the
past expansion of the universe and extrapolate its fate; We have
now embarked on new studies using this approach to constrain
possible theories of this dark energy, by improving both the
statistical and systematic uncertainties of the supernova
measurements.  In particular, I will discuss the proposed new
satellite, the Supernova / Acceleration Probe (SNAP), a 2-meter
class telescope with a wide-field imager and optical-to-near-IR
spectrograph system.