A coincidence measurement then provides evidence of gravitational radiation. In order to determine the source of the signal, a third detector, far from either of the first two, would be necessary. Timing differences in the arrival of the signal to the three detectors would allow triangulation of the angular position in the sky of the signal. The first stage of LIGO, a two detector set-up in the U.S., has been approved by Congress in 1992. LIGO researchers have started designing a prototype detector, and are hoping to enrol another nation, probably in Europe, to fund and be host to the third detector.
All metric models can support gravity waves.
C em in general. However, there is good evidence that C gw is in fact at least almost C em . C em , very close indeed to C em . However, a class of models not yet ruled out experimentally does make other predictions. A definitive test would be produced by LIGO in coincidence with optical measurements of some catastrophic event which generates enough gravitational radiation to be detected.