Why Detect Them?
The gravitational waves that are detectible by LIGO will be caused by some of the most energetic events in the Universe—colliding black holes, exploding stars, and even the birth of the Universe itself. Detecting and analyzing the information carried by gravitational waves will allow us to observe the Universe in a way never before possible. It will open up a new window of study on the Universe, give us a deeper understanding of these cataclysmic events, and usher in cutting-edge research in physics, astronomy, and astrophysics.
Historically, scientists have relied primarily on observations with electromagnetic radiation (visible light, x-rays, radio waves, microwaves, etc.) to learn about and understand objects and phenomena in the Universe. (In recent years, even subatomic particles called neutrinos have begun to be used to study aspects of the heavens.) Each of these sources of information provides scientists with a different and complementary view of the Universe, with exciting new discoveries occurring as each new 'window' has been discovered, introduced, and utilized.
Gravitational waves are not electromagnetic radiation. They are a completely different phenomenon, carrying information about cosmic objects and events that is not carried by electromagnetic radiation. Colliding black holes, for example, emit little or no electromagnetic radiation, but the gravitational waves they emit will cause them to "shine brightly" like beacons on an utterly dark cosmic sea. More importantly, since gravitational waves interact very weakly with matter (unlike electromagnetic radiation), they travel through the Universe virtually unimpeded giving us a clear view of the gravitational-wave Universe. They carry information about their origins that is free of the kinds of distortion or alteration suffered by electromagnetic radiation as it traverses intergalactic space. With this completely new way of examining astrophysical objects and phenomena, gravitational waves will truly open a new window on the Universe, providing astronomers and other scientists with their first glimpses of previously unseen and unseeable wonders, and greatly adding to our understanding of the nature of space and time itself.