Time and tide wait for no man, the saying goes. But at midnight on Tuesday clocks will pause momentarily as the entire planet gains an extra second.
If you happen to be awake, and gazing at the dial on an atomic clock, it will read 23:59:60 before ticking forward to 00.00.00.
The addition of a “leap second” is designed to allow the Earth’s rotation, which is gradually slowing, to catch up with atomic clocks, keeping official time neatly in sync with night and day. But stock market trading floors, tech companies and those in charge of the internet are braced for potentially calamitous glitches linked to the 61-second minute.
“There are consequences of tinkering with time,” said Peter Whibberley, a senior scientist at the National Physical Laboratory (NPL), which is now responsible for defining Greenwich Mean Time. “Because leap seconds are only introduced sporadically it is difficult to implement them in computers and mistakes can cause systems to fail temporarily.”
Last time a leap second was added, on a weekend in 2012, Mozilla, Reddit and LinkedIn all crashed. In Australia, more than 400 flights were grounded as the Qantas check-in system went down.
This is the first time since markets went electronic that the 61-second minute will occur during trading hours.
Dr Leon Lobo, business development manager at the NPL, has been involved in preparations for this evening: “If everyone adds the second in the same way at the same time it shouldn’t cause problems. But if some apply it in a different way or at a slightly different time, you start to have discrepancies. That’s when things trip up.”
The need for leap seconds has arisen because official timekeeping has become so precise. Atomic clocks are roughly a million times more accurate at keeping time than the rotation of the Earth, which fluctuates from day to day and in the long term is slowing down, due to a phenomenon known as “moon drag”.
Leap seconds have been added to the world’s computers around once a year since 1972 – this is the 27th – but this occasion could also be the last. The world’s timekeepers are divided over the issue, with some nations arguing that the addition of rogue seconds has become a liability in a world with an increasing number of financial and communications systems reliant on ever greater precision in timing.
The US and France are pushing to abolish leap seconds, with Britain, Russia and China arguing that the technical challenges are manageable.
“We have always taken the Earth’s rotation as the ultimate reference for timekeeping, and astronomers and navigators still use it,” said Whibberley. “We shouldn’t break the link without carefully weighing the consequences.”
A final decision is due in November at a meeting of the International Telcommunications Union, the relevant UN body.
