Will Earth no longer define time? Leap second could be abolished.
The rotation of the Earth has defined time for as long as time has been kept, but keeping up with all of Earth's little quirks by adding and subtracting an occasional leap second is getting tiring. Timekeepers could vote Thursday to rely solely on atomic clocks.
After millenniums as humanity's timekeeper, Earth may be about to get a pink slip.Skip to next paragraph
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Delegates to the International Telecommunication Union's Radiocommunication Assembly are slated to vote as early as Thursday on a proposal to scrap the leap second – an occasional tweak to atomic clocks designed to sync them with time defined by Earth's rotation.
A "yes" vote, which many expect, would leave atomic clocks as the sole international standard for determining the length of a second, and by extension, a day. For the first time in human history, the length of a day would be uncoupled from Earth's day-night cycle.
The leap second has been used since 1972 to adjust for a long-term slowdown in Earth's rotation. The slowdown is inevitable, but the pace is irregular.
Advocates for the change argue that leap seconds require fiddling with atomic clocks at these irregular intervals, raising the prospect that human error could crash large-scale computer networks, cell-phone systems, and other vital pieces of today's high-tech infrastructure. They rely on highly precise timing to operate.
Critics counter that the leap-second system has worked well since 1972, when the parallel timekeeping process was adopted internationally. Moreover, they say, killing off the leap second merely kicks the need to adjust the clocks down the road, when the gap between the two approaches would be even wider.
Whatever the merits of the case, researchers trace the two-track timing system to its underlying problem: Until the advent of atomic clocks, "the length of a second was not well defined," says John Lowe, group leader for the time and frequency services division of the National Institute of Standards and Technology in Boulder, Colo.
At least in the US, all time was local until the late 1800s. People checked their watches against the time on Town Hall's clock, itself calibrated against local solar time with some tweaking to account for Earth's slightly elliptical orbit around the sun.
With transcontinental railroads came the concept of standard time and time zones. Yet that required a standard unit of time that would allow far-flung stations and conductors to synchronize clocks. That assignment was given to the second, which was defined as 1/86,400 of an average solar day.