Building a better atomic clock

BBC : For eons people measured time by the speed of Earth’s rotation, but that method is not accurate enough for modern timekeeping. In 1967 the second was redefined with respect to the vibrations of cesium atoms. Now researchers have developed an atomic clock that is three times as accurate as the current standard. Instead of using microwaves to get cesium atoms to oscillate, the new optical lattice clock uses a laser to excite strontium atoms. Because laser beams oscillate much faster than microwave radiation, time can be divided into much shorter intervals and thus greater precision can be gained. The new device is so accurate it loses just one second every 300 million years. But, as if that weren’t good enough, another clock is in the works—the ion clock, which, when fully functional, will lose just one second every few billion years.