Laser-chilled mirrors may "see" gravity waves

Gravity, it can be argued, is the force that binds the universe together. It's also a key piece of the theory of general relativity. But, despite its being such a fundamental force, there's no way of measuring it beyond variations on plain old falling down. The Laser Interferometer Gravitational-Wave Observatory (LIGO), being built by the California Institute of Technology (Pasadena, CA) and the Massachusetts Institute of Technology (Cambridge, MA), aims to address that lack by detecting distortions in the shape of space caused by waves of gravity. Similar projects, such as the VIRGO interferometer being built in Italy by French and Italian researchers, have the same goal. To achieve the necessary sensitivity, LIGO and VIRGO must be able to measure very tiny movements—so tiny that even a small temperature change in a mirror could make enough noise to drown out the signal being sought.

Physicists at the École Normale Supérieure and Université Pierre et Marie Curie (both Paris, France) have been working on a technique for reducing the thermal noise in mirrors for gravitational interferometers. They use a laser to measure perturbations in the mirror and apply another beam to damp out the motion through radiation pressure.