The cosmic corkscrew

SOME scientific discoveries defy explanation for years. In the 1880s, for ex-ample, Albert Michelson and Edward Morley tried to work out how the earth moved relative to the universal “ether” that was then supposed to pervade space. This ether, it was believed, was the medium that vibrated when light waves were propagated. Michelson and Morley measured the speed of light at six-monthly intervals (ie, on opposite sides of the earth's orbit around the sun) in the hope that differences caused by the earth moving in opposite directions relative to the ether would indicate something about that peculiar medium. They got the surprise of their lives when they discovered that the speed of light is actually the same whichever direction the earth is travelling in. It took Einstein to work out why: there is no ether; the speed of light is invariable; and, as a result, space and time are variable.