Global time will stop for one second tonight as timing laboratories around the world take steps to ensure the atomic time and the natural time of the Earth stay in sync.
The so-called leap second will be inserted just before midnight tonight, making the final minute of June one second longer.
These adjustments to the Coordinated Universal Time, which take place every few years, make up for the irregularities in the Earth’s rotation. Without them, the Earth’s natural time would keep slipping behind the precise time measured by atomic clocks.
“It’s a very slow divergence that might reach around a minute in a century,” explained Peter Whibberley, senior research scientist at the UK’s National Physical Laboratory’s (NPL) time and frequency group, which is responsible for the insertion of the leap second in the UK.
“It would probably take a thousand years to reach an hour, but it is a steadily increasing divergence. No one quite knows the exact rate because the Earth’s rotation is so unpredictable.”
Insertion of the leap second, however, is a headache for the international time-keeping community, as it could wreak havoc with computer systems and the Internet around the world.
“Sometimes, devices like Internet time servers, running the NTP network time protocol that synchronises time over the Internet, may not handle the leap second correctly,” said Whibberley. “That results in different systems operating with slightly different times and that could have big implications in today’s interconnected world.”
The previous leap second, inserted in 2012, disrupted a number of high-profile websites including Mozilla, Reddit, Gawker, LinkedIn, FourSquare and Yelp.
In Australia, more than 400 Quantas flights were delayed as staff were forced to switch to manual check-ins.
Countries in the east are generally more prone to experience leap second-related issues, as the insertion in these regions happens in the middle of the day.
The problems that leap seconds could cause in today’s interconnected world has led some experts to conclude that the time-keeping community should find a smoother approach to dealing with the discrepancies between the natural and atomic time.
“Some countries, the USA in particular, have been pushing for years to end leap seconds,” said Whibberley. “One of the reasons is that the leap seconds are unpredictable. They are only known around six months ahead at best, so you can’t programme them into a system and that has a possibility of people getting it wrong.”
In November this year, the global time-keeping community will meet at the World Radiocommunications Conference organised by the International Telecommunication Union to decide about the future of the leap second.
As Whibberley admits, the time-keepers are not in agreement over what alternative solution should be implemented.
“In the future, the atomic time may just carry on without leap seconds and slowly diverge from the Earth’s rotation time,” the researcher said. “Some companies, such as Google have come up with ways to smooth out the leap second. Instead of counting the extra second, they actually just stretch out the preceding seconds a few hours beforehand, so that after the end of that period you are aligned with the new time.”
Even if the time-keepers decide to kill the leap second in November, today's leap second will unlikely be the last one ever inserted.
“There will probably be a period of about five years for systems and software to modify,” said Whibberley, who is an advocate of maintaining the leap second in order to keep the link between Earth’s rotation and the atomic time.
The time-keepers insert the leap second through software related to the primary caesium fountain at NPL, without interfering with the physical processes inside the clock.
Leap seconds were first introduced in 1972, by which time atomic clocks and astronomical clocks were already out of sync by 10 seconds. However, in the pre-Internet age, the intervention didn’t present many challenges.
Today, a plethora of time-sensitive systems, including computer programmes and financial markets, rely on the precise ticking of atomic clocks that measure the energy transitions of atoms.
Atomic time celebrated its 60th birthday in June. Read our feature about the atomic revolution in time-keeping and watch our video from the NPL, the birthplace of atomic time-keeping.