Although the change would be mere seconds, Earth’s changing spin threatens to mess with our understanding of time, clocks, and computerized society in unprecedented ways.
That’s why for the first time in history, timemakers may have to consider subtracting a second from our watches in a few years.
According to the study, the planet is rotating somewhat faster than before, and so we may have to subtract one second in a few years. “This is an unprecedented situation and a big deal,” said Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego and lead author of the study.
“It’s not a huge change in the Earth’s rotation that would cause a catastrophe or anything, but it is something noteworthy. “This is another sign that we are in very unusual times.”
Melting ice at both Earth’s poles is counteracting the planet’s explosive motion and this global second is likely to be delayed by about three years, Agnew said.
“We’re headed toward a negative jump,” said Dennis McCarthy, retired U.S. Naval Observatory director at the time, who was not part of the study. “It’s about when.”
It’s a complex situation that involves physics, global power politics, climate change, technology, and two kinds of time.
‘The Earth takes about 24 hours to rotate, but the key word is about.’
For thousands of years, the Earth has generally been slowing down, with the rate varying periodically, said Agnew and Judah Levin, a physicist in the time and frequency division of the National Institute of Standards and Technology.
McCarthy said the slow motion is mostly due to tidal effects, which are caused by the moon’s pull.
It didn’t matter until atomic clocks were adopted as the official time standard 55 years ago. They didn’t slow down.
This established two versions of time – astronomical and atomic – and they did not match. Astronomical time lagged behind atomic time by 2.5 milliseconds every day. This means that the atomic clock will say it is midnight and for Earth it was midnight a fraction of a second later, Agnew said.
Those daily fractions of a second add up to a whole second every few years. Starting in 1972, international timekeepers decided to add a “leap second” in June or December to astronomical time to catch atomic time, called Coordinated Universal Time, or UTC. 11:59 and 59 seconds will be changed to midnight instead. There is another second at 11:59 and 60 seconds. A negative leap second would go from 11:59 and 58 seconds straight to midnight, leaving 11:59:59.
Between 1972 and 2016, 27 separate leap seconds were added as the Earth slowed down. But the rate of slowing was decreasing.
“In 2016 or 2017 or maybe 2018, the rate of recession slowed to the extent that the Earth was actually accelerating,” Levin said.
Why is the Earth’s speed increasing?
Earth is speeding up because its hot liquid core — “a big ball of molten fluid” — acts in unexpected ways, Agnew said, with vortices and flows that vary.
Agnew said the core has been accelerating for about 50 years, but that effect has been offset by the rapid melting of ice at the poles since the 1990s. The melting ice shifts Earth’s mass from the poles toward the bulge’s center, causing rotation to slow down much as a spinning ice skater slows down while extending her arms to her sides, he said.
Agnew calculated that without the effects of ice melting, Earth would need to make that negative jump in 2026 rather than 2029.
Why does this matter for technology?
For decades, astronomers have been keeping together universal and astronomical time with those convenient little leap seconds. But computer systems operators said these additions don’t make up for all the precision technology the world now depends on. Experts said that in 2012, some computer systems handled leap seconds incorrectly, causing problems for Reddit, Linux, Qantas Airlines and others.
“What is the need for this adjustment in time when it causes so many problems?” McCarthy said.
But Russia’s satellite systems rely on astronomical time, so eliminating leap seconds would cause problems for them, Agnew and McCarthy said. Astronomers and others wanted to have a system that would add a leap second when the difference between atomic and astronomical time got close to one second.
In 2022, the world’s timekeepers decided that from the 2030s they would change the standards for inserting or removing leap seconds, making this much less likely.
Levin said tech companies like Google and Amazon unilaterally instituted their own solutions to the leap second issue by gradually adding fractions of a second throughout the day.
“The fights are so serious because the stakes are so small,” Levin said.
Then add the “weird” effect of subtracting rather than adding a leap second, Agnew said. Skipping a second is likely to be more difficult because software programs are designed to add time, not subtract, McCarthy said.
Would a negative leap second really be needed?
McCarthy said the trend requiring negative leap seconds is obvious, but he believes it is related to geologic changes since the end of the last ice age due to the Earth’s rounding.
Three other outside scientists said Agnew’s study was worthwhile, calling his evidence compelling.
But Levin doesn’t think a negative leap second would really be needed. The overall slowing trend from tides has been there for centuries and is continuing, but smaller trends at the Earth’s center come and go, he said.
“This is not a process where the past is a good predictor of the future,” Levin said. “Anyone who makes long-term predictions on the future is in a very shaky position.”
,with AP input,
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Published: 02 April 2024, 10:59 PM IST
