  A brief survey is presented of new science that will emerge during the
decades ahead from direct detection of gravitational radiation. Interferometers
on earth and in space will probe the universe in an entirely new way by
directly sensing motions of distant matter over a range of more than a million
in frequency. The most powerful sources of gravitational (or indeed any form
of) energy in the universe are inspiralling and merging binary black holes;
with LISA data, they will become the most distant, most completely and
precisely modeled, and most accurately measured systems in astronomy outside
the solar system. Other sources range from already known and named nearby
Galactic binary stars, to compact objects being swallowed by massive black
holes, to possible effects of new physics: phase transitions and superstrings
from the early universe, or holographic noise from quantum fluctuations of
local spacetime.
