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A change in time-keeping is coming to Boulder's atomic clocks

World body votes to stop using "leap seconds"
Clock close up
Posted at 11:30 AM, Dec 20, 2022

BOULDER, Colo. — Nobody gets in trouble for being a second late to a meeting. But at the National Institute for Standards and Technology in Boulder, seconds matter. Milliseconds matter. Nanoseconds matter.

Boulder is home to a handful of the world’s atomic clocks, which provide the most accurate definition of a second by counting the oscillations of cesium atoms.

NIST research physicist Jeff Sherman is one of the scientists maintaining the clocks.

“In the modern era there are an amazing number of technologies that under the hood depend on a precise and accurate and remotely synchronized time,” Sherman said.

One example is the Global Positioning System (GPS), which use satellites with their own atomic clocks.

It’s a far cry from the way time was kept for thousands of years, when people used the sun as the timekeeper. But a solar second doesn’t quite match up with an atomic second. So for almost 50 years, scientists have periodically added an extra second to the atomic clocks, to keep them in sync. It’s called a “leap second.”

“The prescription since 1972 has been that leap seconds are announced with about 6 to 8 months notice by an official bureau of astronomers,” Sherman said.

Only 37 leap seconds have been added since 1972. But while rare, they can be problematic.

“You can imagine for computer systems that use digital time signals to stamp the order of operations, for example the order in which financial transactions were made, they can get confused by this sudden addition of a second,” Sherman said.

So why have scientists bothered to keep these different time keeping methods matched up? It turns out there are some who believe the world should respect the ancient ways. But modern life has finally won the debate.

Last month at the General Conference on Weights and Measures, members from around the world voted to end the practice of inserting leap seconds. Sherman hopes this will lead to more consistency in time keeping across technologies.

“A number of technology companies that would rather have a continuous time scale have decided to invent alternate implementations of the leap second,” he said.

The change won’t happen until 2035. For now, no leap seconds are scheduled to be added to the world's atomic clocks for the next 6 months.