Wednesday, February 11, 2009

Keeping Time

Matthew Chalmers in New Scientist on the history of timekeeping and its new accuracy champion - optical atomic clocks. Optical clocks have replaced cesium atomic clocks as the world's best timekeeper. Precise timekeeping is important for a variety of technologies including GPS and will be more important in the future with increasingly complex and automated machines.

Then there is the always startling reality (and title of the piece) that atomic clocks are more accurate than time itself. Einstein demonstrated that time and space are one (spacetime) and that time is not fixed. As speed increases, time slows. Time moves slower (if very slightly) on an airplane, as famously confirmed by Joe Hafele and Richard Keating in 1971 (here is a TIME article previewing the experiment). As gravity increases, time slows. As New Scientist notes, your head ages nanoseconds more than your feet over a year. The incredible precision of atomic clocks will eventually expose time's fickleness, quoting Chalmers: "Soon, if you were to have one of the future ultra-precise atomic-synchronised clocks in your home, the time it told would be different according to how far up the wall it was fixed."

We have discussed Einstein and time before.

(image credit: diagram of advances in timekeeping from New Scientist)