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Just as the classical theory of electricity and magnetism predicts that accelerating charges will give off electromagnetic radiation, general relativity predicts that certain types of systems should give off gravitational radiation. Gravitational radiation is more complicated than electromagnetic radiation. When a gravity wave passes by the geometry of space-time briefly distorts. The types of systems that might produce gravitational radiation are orbiting systems with objects close together or collapsing objects.

Some groups have attempted to detect gravitational radiation directly from astronomical sources, hoping to detect small changes in very large detectors. None of these has been successful yet. More recently, an ambitious program involving laser interferometers to detect small changes is being developed..

The best evidence for gravitational radiation at the time of writing has been indirect. Astronomers have been studying a binary pulsar system (to be discussed in Chapter 12), in which the system appears to be losing orbital energy at exactly the rate that would be predicted for gravitational radiation.