Clocks May Lose a Second by 2029

Clock Face
Clock Face | Image by Olena Ruban/Getty Images

International timekeepers are considering subtracting a second from the atomic clock for the first time in history.

Leap seconds are added to Coordinated Universal Time (UTC) on a fairly regular basis to keep atomic clocks synchronized with astronomical time (UT1). A leap second is added, on average, about every year and a half since the practice started in 1972. The extra second is typically added at the end of December or June on the last second of the UTC day, per the National Institute of Standards and Technology (NIST).

One reason for the discrepancy between the two types of timekeeping methods is that the Earth’s rotation is not constant, sometimes speeding up and sometimes slowing down. This is caused by the eddies and flows of the Earth’s molten core, which acts in unpredictable ways, according to geophysicist Duncan Agnew at the Scripps Institution of Oceanography.

In the past, the Earth’s rotation has trended gradually slower, leading to the need to add a leap second from time to time, according to NIST.

“So far, there have only been positive leap seconds. However, there is a provision for negative leap seconds if it becomes necessary due to changes in Earth’s rotation,” the NIST’s website states.

But the negative leap second may indeed become necessary within the next five years or so because, in more recent times, the Earth’s rotation has begun speeding up.

According to a new analysis authored by Agnew, the need to subtract a leap second is predicted to arise around 2029.

Scientists will likely spend the interim determining how to cope with the havoc that the adjustment may produce in computing.

“We do not know how to cope with one second missing. This is why time meteorologists are worried,” said Felicitas Arias, the former director of the Department of Time at the International Bureau of Weights and Measures in France.

“This is an unprecedented situation and a big deal,” said Agnew, according to Fox 4. “It’s not a huge change in the Earth’s rotation that’s going to lead to some catastrophe or anything, but it is something notable. It’s yet another indication that we’re in a very unusual time.”

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