Their time has come

THE phrase “clockwork universe” is more than a pithy tribute to the exactitude of physics. For thousands of years, the movement of the heavens (or rather, as was eventually realised, the movement of the Earth within the heavens) served as exactly that—a clock. It still does. Even the hyper-accurate atomic clocks now used to record the passage of Coordinated Universal Time (UTC), the globe's official standard, regularly defer to the addition of so-called leap seconds. These are introduced every so often by the time lords of the International Earth Rotation and Reference Systems Service. Their purpose is to match the relentless stream of regular 86,400-second days that pour out of atomic clocks with the slight irregularities that the Earth experiences in its rotation around its axis.

But possibly no longer. Next week, the International Telecommunication Union (ITU) is meeting in Geneva, and one of the items on its agenda is the abolition of the leap second. If the assembled delegates vote in favour, then the next leap second (which will be added one second before midnight on June 30th, causing clocks set to UTC to display 23:59:59 for two seconds instead of one) will be one of the last—and the answer to the question “what time is it?” will have ceased to have anything to do with the revolutions of the heavens.