Adam Frank for McGraw-Hill

What do you think of when you hear the word `Telescope'? For most people the term conjures up images of a long tube with glass lenses mounted on both ends. Maybe there is a pirate and talking parrot floating around too. For others, a telescope is a metal spider work structure surrounding a giant mirror, housed in a dome, perched on some high, wind-swept mountaintop. This is the astronomical image, the telescope as a lonely sentinel scanning the night sky for dim traces of distant cosmic events. There is nothing wrong with this picture and for hundreds of years it is exactly what astronomical telescopes were all about. They were light buckets collecting photons in the service of knowledge. Now, however, things are changing. The definition of telescope is beginning to move into some entirely new territory and our understanding of the Universe may go along for the ride.

In the beginning a telescope was really only about one kind of light, the visible kind with our eyes were already built for. Then people realized that visible light was just one form of electro-magnetic radiation. The violets, greens, and reds of the rainbow are a tiny slice of all the different kinds of possible electro-magnetic waves. This was amazing news for astronomers because it meant that the Universe we see with our eyes and through our optical telescopes was just one chapter in a much richer story. Astronomers realized that there were other wavelength "windows" through which to view the sky. Unfortunately, they had to wait until radio telescopes were built before they had a chance to actually "see" the cosmos through one of those windows. The first radio telescopes provided an astonishing insight. The heavens look different through different wavelength windows - the radio "sky" and the optical "sky" are not the same. There are objects pumping out psychotic amounts of power in radio wave light that are just pipsqueeks in optical light.

In time astronomers built increasingly complex and sophisticated instruments that let them open up other wavelength windows. There are now telescopes for almost all the new skies one can imagine: Infrared; Ultra-violet; X-ray; Gamma rays. Each new view of the heavens has blown the doors off any complacency we might have been lulled into. Since the protective blanket of the Earth's atmosphere does such a great job of shielding us from many forms of electro-magnetic radiation, some of these new telescopes have been lofted into space to become orbiting observatories. But even the most advanced orbiting X-ray satellites still has one critical feature in common with the first crude telescopes built in the 1600s. They all use electro-magnetic waves. They are all light detectors. After 400 years one can ask if that is the limit of a telescope's definition? Couldn't the Universe be sending us some other kind of signal?

On the planes of Eastern Washington and the delta farmland of Louisiana a new kind of telescope is being built. It's called LIGO, which stands for the Laser Interferometric Gravity Observatory. LIGO won't catch light waves. Instead it's designed to feel waves in the structure of Space-Time itself. These are called "gravity waves", ripples in the fabric of reality, distortions in the structure of space itself. Gravity waves are a direct prediction of Albert Einstein's greatest work, the General Theory of Relativity. What makes gravity waves so exciting and such a wonderful tool, if they could be detected, is that they are expected to emerge from Universe's most exotic and violent phenomena.

Gravity waves are produced when very massive objects do very extreme things. Astronomers expect copious gravity waves to emerge from the collisions of neutron stars or even black holes. To catch the gravity waves from these events astronomers have to push technologies to new limits. LIGO does not look anything like a conventional telescope. It consists of finely tuned lasers traveling across many miles in underground tubes. The lasers are designed to sense the stretching of Space-Time by passing gravity waves. By passing the lasers back and forth through evacuated tubes astronomers hope to detect minute distortions in the fabric of Space-Time accurately enough to determine the nature and origin of the gravity waves that produced them. If LIGO can detect the gravity signature of events such as colliding black holes it will reveal an entirely new facet of the Universe's many storied face.

LIGO is just one of a handful of new telescopes that do not use light. There are neutrino telescopes and cosmic ray telescopes that are either in operation or being built. By the time your grandchildren are born the word telescope may bring many different images to mind. Even more amazing, the word Universe may have gone through a similar transformation!

Black Hole Collision Website
http://jean-luc.aei-potsdam.mpg.de/(en)/Press/BH1999/