Ripples in Spacetime; April 2002; Scientific American Magazine; by W. Wayt Gibbs; 10 Page(s)
HANFORD, WASH., AND LIVINGSTON, LA.-A chill January wind sends a shiver through Frederick J. Raab as he stands, binoculars to his eyes, on a mound near the center of the LIGO Hanford Observatory. He runs his gaze northward down a ruler-straight concrete tunnel to a building four kilometers to the north: there is one end of the observatory. Pivoting 90 degrees, Raab pans westward across the sagebrush-stubbled desert until he spots an identical tube and another building, also four kilometers distant. "When we talk about locking the laser beam" that shines inside those tubes, Raab says, "we mean holding the light waves steady to better than the width of an atom-over that distance."
Raab oversaw the construction of this giant try square, one of a pair that are the largest, most expensive and-if they fulfill the ambition of their designers-most sensitive detectors yet to join the 40-year hunt for gravitational waves. Part ruler, part clock, these two instruments are spacetime meters that will attempt to record how the continuum is rattled by the most violent cataclysms in the universe: detonating stars, colliding black holes, perhaps phenomena not yet imagined. As these ripples expand outward at the speed of light, they alternately stretch and squeeze space, causing the distance between free-floating objects to expand and contract. But by the time the vibrations reach the earth, theorists estimate, they are so unsubstantial that they alter distances by less than one part in a trillion billion.