General Relativity

Gravitational Wave Research

Gravitational waves are one of the features of General Relativity. The brightest gravitational wave sources are objects with strong gravitational fields, so the study of the gravitational waves is a study of General Relativity. To date, no experiment has detected a gravitational wave, but many experiments are now making the attempt.

Cryogenic Resonant Bar Detectors. The first device developed to study gravitational waves was the resonant bar detector. First developed in the 1960s, the devise is simple a solid metallic cylinder with electronic devices attached at the end to measure the acoustic waves in the bar. Current versions cool the bar to several degrees Kelvin. These devices attempt to observe gravitational waves at just below 1kHz. (continue)

Michelson Laser Interferometers.The Michelson laser interferometer is a second device that is used as a gravitational wave detector. The most effort and money in graviatational wave research have gone into these detectors. With sizes of several kilometers, these are highly sophistocated versions of the device developed by Michelson to test for the existence of the electromagnetic aether. (continue)

Ground-based Michelson Interferometers. A number of Michaelson interferometers are now in operation, and several more are under development. Among the experiments now taking data are LIGO in the U.S., GEO in Germany, Virgo in Italy, and TAMA in Japan. These devices are sensitive to gravitational wave above 10 Hz. (continue)

Results from Ground-based Interferometers. Results have been released from the first two data runs of LIGO. The upper limits places on the gravitational radiation from sources remain far above what is necessary to constrain the theories of gravitational wave sources. (continue)

LISA, a Space-Based Interferometer. The most expensive experiment under development is the LISA project, which intends to use three spacecraft in orbit around the sun as test masses of a triangular interferometer. This joint project between ESA and NASA is expected to have the interometer in space by around 2012. This device is expected to observe gravitational waves with frequencies between 0.0001Hz and 0.1Hz. (continue)