  Gravitational wave detectors capable of making astronomical observations
could begin to operate within the next year, and over the next 10 years they
will extend their reach out to cosmological distances, culminating in the space
mission LISA. A prime target of these observatories will be binary systems,
especially those whose orbits shrink measurably during an observation period.
These systems are standard candles, and they offer independent ways of
measuring cosmological parameters. LISA in particular could identify the epoch
at which star formation began and, working with telescopes making
electromagnetic observations, measure the Hubble flow at redshifts out to 4 or
more with unprecedented accuracy.
