150 years since James Clerk Maxwell showed that electric and magnetic fields create waves of light, and 100 years after Einstein created his theory of gravity (general relativity) gravitational waves have been discovered. The announcement came at the American Association for the Advancement of Science, in Washington DC on Thursday 11th February. This is the climax of an experiment that began in 2002, which was then rebuilt to a new sensitivity in September last year. Almost immediately last autumn, rumours began that the detector was responding to gravitational waves. Now, at last, we have the confirmation of this major missing piece of Einstein’s general relativity theory.
For almost a century, physicists have debated whether the gravitational field creates waves analogous to what happens for electromagnetic fields? If so, what are they like; do they travel at the same speed as light or, as the sceptic Arthur Eddington famously opined: “at the speed of thought.” In the opinion of many scientists, the discovery of gravitational waves would be the final piece in the jigsaw of general relativity theory and a certainty for a Nobel Prize.
In Einstein’s universe, space and time are intimately entwined into an elastic medium—“space-time”—According to general relativity, space-time becomes warped when massive bodies, such as planets and stars, are present. If the mass that is the source of a gravitational field suddenly shifts, as in a supernova explosion, or when two black holes swirl and merge, gravitational waves should spread throughout the medium.
This sort of behaviour is familiar in electromagnetism, thanks to Maxwell. An oscillating charge in a radio antenna, for example, emits waves…