New Clock Promises to Be World's Most Precise

July 13 -- The most accurate clocks today slip by only one second every 30 million years.

For scientists at the National Institute of Standards and Technology in Boulder, Colo., that's just not accurate enough.

Instead, they've built a clock designed to only slip by a second once every 30 billion years. This clock (which would never fit on the wrist, since it takes up the size of a large lab room) records time by counting the rapid-fire oscillations in a laser. The oscillations, in turn, are kept in pace by a single mercury atom that vibrates at a constant cadence.

The result is a clock that counts time by the femtosecond — a millionth-billionth of a second.

"This has the potential for making frequency and time measurements more precise by orders of magnitude than current clock systems," says Jim Bergquist, a physicist at NIST and co-author of a study about the new optical clock in this week's journal Science.

How to Keep Time

All clocks operate using two main ingredients. The first is something that creates a regular, periodic event, and the second is a device that will count, accumulate and display those events.

In a grandfather clock, for example, a pendulum swings once every second and those swings are recorded by metal gears inside the clock. In quartz watches, time is measured by the oscillations of a quartz crystal and usually recorded using digital counters. Digital clocks use either the oscillations on the power line (60 cycles a second in the United States) or the oscillations of a quartz crystal and also count using digital counters.

The most accurate clocks today measure time by locking the frequency of microwave beams to the frequency of vibrating atoms. Rather than swinging once per second, like the grandfather clock, Cesium 133 atoms oscillate at a rate of 9,192,631,770 times a second.

Since 1967, the cesium atomic clock has defined "one second" as the time it takes a cesium atom to vibrate 9,192,631,770 times.

Before the atomic clock, the second was based on less precise measurements of the motion of the Earth.