Changes in the Earth’s rotation threaten to toy with our sense of time, clocks, and computerized society in unprecedented ways, but only for a moment.
For the first time in history, the world’s timekeepers may have to consider subtracting a second from their clocks in a few years, as the Earth is spinning a little faster than before. Around 2029, clocks may need to jump by one second, known as a “negative leap second,” according to a study published Wednesday in the journal Nature.
“This is an unprecedented situation and a big deal,” said study lead author Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego. “It’s not a huge change in the Earth’s rotation that would cause a catastrophe or anything, but it’s worth noting. This is another sign that we are in very unusual times.”
This image is provided by NOAA/NASA. This May 31, 2018 satellite image, created by the new GOES-17 satellite using the Advanced Baseline Imager (ABI) instrument, shows Earth’s Western Hemisphere on May 20, 2018 at 12:00 PM EDT . . For the first time in history, the world’s timekeepers may have to consider subtracting one second from their clocks in the next few years, as the Earth is spinning a little faster. (NOAA/NASA via AP, File)
Agnew said melting ice at the Earth’s poles is hampering Earth’s explosive speed, likely delaying this global countdown by about three years.
“We’re heading towards a negative leap second,” said Dennis McCarthy, former U.S. Naval Observatory time director who was not involved in the study. “It’s just a matter of when.”
This is a complex situation involving physics, global power politics, climate change, technology, and two types of time.
The earth takes about 24 hours to rotate, so the key word is “about”.
Agnew and Judah Levin, physicists in the Time and Frequency Division at the National Institute of Standards and Technology, say that over thousands of years, the Earth has generally slowed down, with speeds varying from time to time.
McCarthy said the slowdown is primarily due to tidal effects caused by the moon’s gravitational pull.
This wasn’t an issue until atomic clocks were adopted as the official standard time more than 55 years ago. They didn’t slow down.
This established two versions of time (astronomical time and atomic time), which did not coincide. Astronomical time lags atomic time by 2.5 milliseconds each day. That means when the atomic clock strikes midnight, it will be midnight for Earth a fraction of a second later, Agnew said.
The fractional parts of seconds each day add up to a whole number of seconds every few years. Starting in 1972, the International Timekeeping Organization decided to add a “leap second” to astronomical time in June or December to catch up with atomic time, called Coordinated Universal Time (UTC). Instead of 11:59:59 changing to midnight, an additional second occurs at 11:59:60. A negative leap second would skip 11:59:59 and go from 11:59 and 58 seconds to midnight.
Between 1972 and 2016, 27 separate leap seconds were added as the Earth slowed. However, the speed of deceleration was gradually slowing.
“In 2016 or 2017, or maybe 2018, the Earth’s velocity slowed to the point where it was actually accelerating,” Levine said.
Earth’s speed is accelerating because its hot liquid core (a “big ball of molten fluid”) interacts in unpredictable ways with changing eddies and currents, Agnew said. Ta.
Agnew said the core has been causing the acceleration for about 50 years, but the rapid melting of polar ice since 1990 has masked its effects. As the ice melts, the Earth’s mass moves from the poles to its bulging center, slowing its rotation in the same way that a spinning ice skater slows down when he stretches his arms out to the side, he said. .
Without the effects of melting ice, Agnew calculated that Earth would need a negative leap second in 2026 instead of 2029.
For decades, astronomers have recorded universal astronomical time with a convenient little leap second. But computer system operators said such additions will not be easy with all the precision technology the world currently relies on. Experts say some computer systems mishandled leap seconds in 2012, causing problems for Reddit, Linux, Qantas and more.
“What is the need for this adjustment to happen in time when there are so many problems?” McCarthy said.
But Russia’s satellite system relies on astronomical time, so eliminating leap seconds would create problems, Agnew and McCarthy said. Astronomers and others wanted to maintain a system that added a leap second every time the difference between atomic time and astronomical time approached one second.
In 2022, the world’s timekeeping organization decided to change the criteria for inserting or deleting leap seconds starting in the 2030s, making leap seconds much less likely.
According to Levine, tech companies like Google and Amazon have unilaterally come up with their own solutions to the leap second problem by incrementally adding up fractional seconds over the course of an entire day.
“The fight is very serious because the stakes are very small,” Levine said.
Agnew said they will then add a “bizarre” effect that subtracts leap seconds instead of adding them. Skipping seconds is likely to be more difficult because software programs are designed to add time rather than subtract it, McCarthy said.
McCarthy said there is a clear trend toward the need for negative leap seconds, but he believes it has more to do with geological changes since the end of the last Ice Age that have made the Earth more round. .
Three other outside scientists said Agnew’s work made sense and argued his evidence was convincing.
But Levine doesn’t think negative leap seconds are really necessary. He said that while the overall trend of tidal slowing has existed for centuries and continues today, the shorter trend in the Earth’s core has come and gone.
“This is a process in which the past is not a good predictor of the future,” Levine said. “Anyone who makes long-term predictions about the future is in a very precarious position.”
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