After decades of discussion, quibbles and concern over computer system clocks, the world’s official timekeepers voted to replace what many considered a tedious correction: the leap second. It is time, they say, for leap time.
Delegates from 69 countries voted Thursday at a conference in France of the International Bureau of Weights and Measures, which ensures the world follows the same standards for time, weight, distance and more.
The decision to adopt leap time starting next year is aimed at reducing the risk that computers and other technical systems will stumble as their software grapples with minutes lasting 61 seconds — and, worse, 59 seconds — instead of about 60 seconds.
“After 30 years of debate, leap second is giving way to leap time,” said Dr Setnam Shemar, senior scientist in the Department of Time and Frequency at the UK’s National Physical Laboratory (NPL). “This will reduce risks to national systems and infrastructure that rely on precise time while preserving the fundamental connection between our global time system and the rotation of the Earth.”
The Versailles vote means that Coordinated Universal Time (UTC) can deviate by up to an hour from astronomical time before a leap hour is necessary, but this is unlikely to happen for thousands of years.
“We already have daylight saving time where we change by an hour and it doesn’t bother anyone except losing sleep or sleeping an extra hour,” said Shemar, who served on the international committee of timekeeping experts that proposed leap time.
The more familiar leap year was introduced more than 2,000 years ago to ensure that the calendar year did not lag behind the time it takes the Earth to circle the sun. Adding a day at the end of February every four years or so is enough, because the Earth orbits the sun every 365 and a quarter days.
Leap seconds are a much more modern invention. In 1955, Louis Essen and Jack Parry of the NPL built the world’s first practical, high-precision cesium atomic clock. This device revolutionized the measurement of time and, in 1967, the astronomical definition of the second, based on the rotation of the Earth, was abandoned. Since then, the formal definition of a second is 9,192,631,770 vibrations of the cesium atom.
Atomic clocks are exceptionally stable and precise. Their timing has become essential for modern computer systems, communications, satellites, commercial systems and power grids. But the Earth’s rotation is much less reliable. Its rotation is affected by the planet’s molten core, shifting oceans, global jet streams, and other natural forces.
Generally speaking, the Earth’s rotation is slowing down: when an asteroid doomed the dinosaurs, a day lasted about 23 and a half hours. For this reason, authorities have added 27 leap seconds since 1972 to ensure that UTC is aligned with astronomical time.
This strategy lasted for more than 50 years until scientists discovered a new reason to fear technological chaos. Over the past decade, the Earth’s rotation has accelerated, meaning authorities might have had to add the first negative leap second, which is the equivalent of knocking a second off UTC. The 30% probability of a negative leap second in the next decade pushed the Versailles vote forward.
“Leap seconds can be quite tricky to deal with,” Shemar said. Telecommunications, power grids and navigation systems used high-precision timing, he explained, but software updates could apply leap seconds at the wrong time, throwing networks out of sync.
after newsletter promotion
“After the leap second was implemented in 2012, some computer systems couldn’t handle 61 seconds per minute. Servers froze, they seized up. Systems went offline. And those are the kinds of outages that can happen with positive leap seconds,” Shemar said.
Among the downed websites were Reddit and LinkedIn. In addition, Qantas flights have been affected by delays. Negative leap seconds carry even greater risks. “There might be software that hasn’t been tested on negative leap seconds because we’ve never needed to apply one before,” Shemar said.
Testing every computer system that communicates with each other in the world would cost businesses a fortune. It was this concern that swung the vote.
Historically, the United Kingdom has complained about the retention of leap seconds because of the connection to Greenwich Mean Time. Russia also opposed the move, citing concerns about the impact on its Glonass satellite navigation system.
The IERS Earth Orientation Center in Paris tracks changes in Earth’s rotation and other movements that drive UTC. The center also issues notices when leap seconds need to be added.
Dr. Christian Bizouard, director of the center, approved the vote, but said the decision would be conveyed to people in the distant future. “It’s kind of a philosophical discussion, because if leap hour happens, it won’t be for a long, long time,” he said. “What we are doing is postponing the decision.”
Gn headline
