IF EINSTEIN was right, space is constantly squeezed and stretched by traveling waves of warped space, gravity waves emanating like pond ripples through the universe from violent phenomena such as exploding stars, collisions between black holes or between dense, massive, burned-out neutron stars and other cosmic cataclysms. Sprawling $350 million gravity wave catchers Laser Interferometric Gravity-Wave Observatory (LIGO) identical L-shaped structures, one in Louisiana between Baton Rouge and New Orleans, the other near Hanford WA, have 2-mile-long arms stretching at right angles across flat, desolate ground longer than 40 football fields. Patterns of waves caught would reveal more about black holes and the origin of the universe. Even as theoretical entities gravity waves inspired years of study. What would they look like if we could detect them? It's 2 years of fine-tuning before gravity waves register in either detector, not an experiment but a new kind of telescope opening a previously opaque window into the cosmos, imaging a whole different universe. Radio antennas, X- and gamma-ray satellites and infrared detectors reveal phenomena invisible to ordinary telescopes. Gravity waves are among the universe's most subtle phenomena. Even the biggest waves reaching Earth expand and contract space less than the diameter of an atomic nucleus. LIGO's designers think they can measure it.
Deep-space ballet
Black holes collide with surprising frequency. Crowded star clusters are meeting places for stars and black holes, bringing pairs close enough to capture each other in orbit and slowly spiral together. Black holes meet every million years in the Milky Way. LIGO catching waves from a region encompassing several million galaxies would detect black hole collisions every year. In 1917 Einstein published his general theory of relativity. At first physicists tried to detect Einstein's waves in metal bars interspersed with special crystals generating electricity when squeezed. Bar detectors never achieved needed sensitivity. Late 1970s, LIGO's first visions: Mirrors suspended near the ends of the arms move closer together and farther apart when gravity waves pass through. Lasers beamed up and down the arms measure even the slightest deviation in distance. The problem is even a monster gravity wave would move the mirrors less than the diameter of an atomic nucleus, trillionths of a trillionth of an inch. The mirrors must be as perfectly still as physics laws allow. Even a few air molecules could nudge the mirrors enough to ruin the experiment. The vacuum system alone cost $85 million.
Delicate devices
Designers also protect LIGO from random seismic activity, passing trucks, landing airplanes and other disturbances. Only a gravity wave should move these mirrors. Black holes are by definition invisible, their gravity so powerful even light can't escape. Gravity waves know no such bounds. They're free to escape with a message about the structure of the black hole, real signatures of black holes, mapping the space-time curvature around a black hole. Black holes are made not of matter but of pure space-time curvature, like a dent or bump in the fabric of space. Although telescopes seeing millions of light-years into space see millions of years back in time the early universe is shrouded from view of any instrument sensitive to light.