The world’s timekeeping body had a gentle phase-out plan for the leap second “but now there is a spanner – or spinner – in the works”, said the Financial Times.
The Earth has been rotating unusually rapidly for the past decade, meaning there’s a chance that, before the phase-out in 2035, we’d actually need a negative leap second – deleting a second, rather than adding one. This has never been attempted before and could “create mayhem in the digital time-stamped continuum”. So, the governing body of the International Bureau of Weights and Measures is this week urgently considering condemning the leap second “to an earlier grave”.
What are leap seconds? “For millennia, a day has been defined as one full rotation of the Earth,” said physics and astronomy professor Vahe Peroomian on The Conversation. Ancient Egyptians were the first known civilisation to divide day and night into 12 parts each, establishing the 24-hour day. Astronomers then built the system of minutes and seconds that, centuries later, devices such as pendulum clocks and quartz watches were able to measure.
But because the speed of the Earth’s rotation can fluctuate, defining a second as a fraction of a solar day is imprecise. In 1967, the General Conference on Weights and Measures adopted a new definition of a second based on the steady oscillations of the cesium-133 atom. To keep this new Coordinated Universal Time (UTC) in sync with Earth’s rotation, timekeepers then invented the leap second in 1972. Once the lag between astronomical time and UTC reaches a certain point, a leap second is inserted to realign them. This has happened 27 times since 1972, with the most recent leap second inserted in 2016.
Why are they being phased out? Leap seconds have become “increasingly difficult to deal with in the computer age”, said ABC News. They can disrupt computer operating systems, which assume a day is always 86,400 seconds long, resulting in glitches and outages. But the prospect of the first negative leap second poses an even greater risk. “Many computer programmes assume all leap seconds are positive,” Setnam Shemar, the UK’s principal timekeeping scientist, told the FT. Removing a second could “result in a major technology failure in telecommunications or electricity grid networks or satellite navigation systems”.
If they do decide to ditch the leap second, the world’s timekeepers will vote on introducing a “leap hour” instead. This could take “a millennium or more” to accumulate and, by then, life may be so different, there may be no need to adjust the lag at all.
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