Einstein’s theory of gravity is much larger than Newton’s. it does away with the idea that the effects of gravity are instantaneously communicated from one side of the Universe to the other and incorporates the restriction that information cannot be sent at speeds faster than that of light. This allows gravity to spread its influence by means of waves traveling at the speed of light. These gravitational waves were predicted to exist by Einstein and there is little doubt that they do exist. Although they are too weak to detect directly on earth today, their indirect effects have been observed in a binary star system containing a pulsar. The pulsar is like a lighthouse beam spinning at high speed. Every time it comes around to face us we see a flash. Its rotation can be very accurately monitored by timing observations of its period pulses. Twenty years of observations have shown that the pulsing of the binary pulsar is slowing at exactly the rate predicted if the system is losing energy by radiating gravitational waves at the rate predicted by Einstein’s theory (Figure 6.3)

In the next few years, ambitious new experiments will attempt to detect these waves directly. They are like tidal forces in their effects. When a gravitational wave passes through the page that you are reading it will slightly stretch the book sideways and squeeze it longways without changing its volume. The effects is tiny but with elaborate apparatus, similar to the interferometer used by Michelson en.wikipedia.org/wiki/Michelson_interferomete r to test the existence of the ether, we may be able to detect gravitational waves from violent events far away in our own galaxy and beyond. The prime candidates for detection are waves from very dense stars or black holes that are in the final throes of circling each other in orbits that are getting closer and closer to each other. In the end they will spiral together and merge in a cataclysmic event that produces huge amounts of outgoing light and gravitational waves. In the far future the binary pulsar will collapse into this state and provide a spectacular explosion of gravitational waves. Pages 173-175