Astrophysics: A Mystery Ticking Slower

After Cambridge University astronomers announced the discovery of pulsars last February, scientists conjured up widely differing theories about the nature of the mysterious radio sources. There was unanimity about only one point: pulsars beeped with clocklike regularity. The pulses from space seemed so precisely timed that some scientists advocated their use as a universal time standard more accurate than even an atomic clock. Others suggested that the signals could provide a reliable timing device for astronauts on distant missions or for experimental checks on the theory of relativity. Now new discoveries...