I enjoyed Philip Bucksbaum's enthusiastic reference to the precision measurements attained by LIGO, the Laser Interferometer Gravitational-Wave Observatory (Physics Today, June 2006, page 57). Bucksbaum and your readers may be pleased to know that these achievements were actually understated.
LIGO instruments detect changes less than a thousandth of a proton diameter over a distance of 4 km. A proposed LIGO upgrade is expected to improve displacement sensitivity by a further order of magnitude.
The Laser Interferometer Space Antenna, a planned space-based detector, will not have such fine displacement resolution, but it will span 5 million km, so its strain sensitivity will be comparable to LIGO's. LISA's greater length means space and terrestrial experiments will sample complementary, nonoverlapping frequency ranges, and thus target different realms of astrophysics.
