Gravity Wave Detectors

First off, we are pretty close to certain that gravity waves exist.
Indirect evidence has been supplied by the Binary Pulsar (PSR1913+16). The emphasis for the next generation of devices is to detect gravitational waves directly and to use gravitational waves as probes of the physics of strong gravitational fields.

The next generation of gravitational wave expermients, Earth-bound interferometric experiments, are coming online or soon to be online (LIGO, TAMA, GEO, VIRGO, and AIGO). The experiments use Michelson interferometers to search for gravity waves.

The gravity wave as it passes by the detector, alternately stretches and squeezes each arm. The squeeze and stretch is exceedingly small, a tiny fraction of the wavelength of the laser light, but nonetheless is measurable if the arms (path lengths) are large enough.

The U.S. experiment is the Laser Interferometer Gravitational Wave Observatory (LIGO),

Above is shown the U.S. LIGO site at Hanford, WA. The University of Oregon group composed of physicists Dr. Brau, Dr. Frey, and Dr. Strom are part of the LIGO collaboration working on the Hanford part of project.

The arms of the interferometers are on the order of 4 kilometers in length with the beams reflected in the cavities around 50 times to increase the effective size. This effective size detemines the GW frequencies to which LIGO is sensitive.

How do these levels compare to some theoretical predictions?
LIGO is most sensitive to high frequency GW. LIGO is thus most sensitive to sources which have small sizes and LIGO is most likely to detect things on the scale of neutron stars and black holes. LIGO will not be able to detect the GW emission from (non-merging) binary systems like PSR1913+16, because such binary systems are just too darn big. This is unfortunate because we are almost lead-pipe certain that PSR1913+16 produces GW radiation. The space-based GW Observatory, LISA, will be sensitive to such sources of GW emission.