The atomic clock (Image:

Official timekeepers added an extra second to 2008, so that our super-precise atomic clocks match, more or less, Greenwich Mean Time. In this special podcast from "The World," Clark Boyd interviews David Rooney, Curator of Timekeeping at the Royal Observatory in Greenwich, England.

Since the early 1970s, the atomic clock enthusiasts and the GMT timekeepers have struck a deal by adding "leap seconds" when needed. Rooney says the last time a leap second was added was in 2005, and this happens every two or three years because: "It's a neat trick to keep our clocks in sync with the sun, to keep the fearsomely accurate atomic clocks that we base our lives on ... that we base a lot of our technologies on, in sync with the much less accurate time-keeping, and that's ... the rotation of the earth ... Greenwich Mean Time being the basis of that.

"We still want the time on the clocks to match the time by the sun, because that's what we're hard-wired to, as animals, so we have ... the leap second to tie the two together, so they're never more than a fraction of a second apart."

Some argue that it's time to ditch GMT entirely, and let the atomic clocks rule our lives. But you can see the problem -- temporal drift. In time (and we're talking 600 or 700 years, give or take) atomic time and GMT would get so far apart that when the Brits take their afternoon tea, the clock would be reading three a.m.


PRI's "The World" is a one-hour, weekday radio news magazine offering a mix of news, features, interviews, and music from around the globe. "The World" is a co-production of the BBC World Service, PRI and WGBH Boston.

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