Ripples in space-time could provide clues to missing components of the universe

Virgo and Ligo are two Michelson type laser interferometers with two arms of 3 and 4 km, respectively, at right angles. A semi-transparent mirror divides the incident laser beam into two equal components sent into the two interferometer arms. In each arm a Fabry-Perot resonant cavity formed by two mirrors extends the optical length to about 100 kilometers due to the multiple reflections of the light and therefore amplifies the small variation of distance caused by any gravitational passage. The