Have you ever felt like there isn’t enough time in the day? As it turns out, you may be onto something. The Earth is rotating faster than it has in the last half-century, causing our days to be slightly shorter than we are accustomed to.
And, despite the fact that it is an infinitesimally small difference, it has become a major source of consternation for physicists, computer programmers, and even stockbrokers.
We all know it takes around 24 hours for Earth to complete one whole rotation on its axis, however, a UK National Physical Laboratory scientist in a conversation with Discover Magazine warns that Earth is now spinning faster than it did half a century ago.
A day is defined as 86,400 seconds, or 24 hours – the time it takes the Earth to complete one rotation. The Earth, on the other hand, does not rotate perfectly uniformly. Typically, the Earth’s rotation slows, increasing the length of the day by about 1.8 milliseconds per century on average. This means that a day only lasted 21 hours 600 million years ago.
The variation in day length is caused by a number of factors, including the Moon’s and Sun’s tidal effects, core-mantle coupling within the Earth, and the overall distribution of mass on the planet. Seismic activity, glaciation, weather, oceans, and the Earth’s magnetic field can all have an impact on the length of the day.
A startling discovery was made by scientists in 2020. They discovered that, rather than slowing down, the Earth has begun to spin faster. It is now spinning faster than it has in the previous 50 years. In fact, the three shortest 28-day periods on record all occurred in 2020.
Why Earth rotates?
Around 4.5 billion years ago, a dense cloud of interstellar dust and gas collapsed in on itself and began to spin. Because of angular momentum — essentially, “the tendency of the rotating body to continue rotating until something actively tries to stop it,” explains Peter Whibberley, a senior research scientist at the UK’s National Physical Laboratory — there are remnants of this original movement in our planet’s current rotation.
Our planet has been spinning for billions of years due to angular momentum, and we experience night and day. However, it has not always spun at the same rate.
Earth made about 420 rotations in the time it took to orbit the Sun hundreds of millions of years ago; we can see evidence of how each year was jam-packed with extra days by examining growth lines on fossil corals. Although days have gradually grown longer over time (due, in part, to how the moon pulls at Earth’s oceans, which slows us down a bit), during humanity’s watch, we’ve remained consistent at about 24 hours for a full rotation — which translates to about 365 rotations per trip ’round the Sun.
However, as scientists have gotten better at observing Earth’s rotation and keeping track of time, they’ve discovered that there are only minor fluctuations in how long it takes to complete a full rotation.
A new way to track time
Scientists developed atomic clocks in the 1950s that kept time by observing how electrons in cesium atoms fell from a high-energy, excited state back to their normal ones. Because the periods of atomic clocks are generated by this unchanging atomic behavior, they are not affected by external changes such as temperature shifts in the same way that traditional clocks are.
Over time, however, scientists discovered a flaw: the unmistakably accurate atomic clocks were deviating slightly from the time that the rest of the world observed.
“As time goes on, there is a gradual divergence between the time of atomic clocks and the time measured by astronomy, that is, by the position of Earth or the moon and stars,” says Judah Levine, a physicist in the time and frequency division of the National Institute of Standards and Technology. Basically, a year as recorded by atomic clocks was a bit faster than that same year calculated from Earth’s movement.
“In order to keep that divergence from getting too big, in 1972, the decision was made to periodically add leap seconds to atomic clocks,” Levine says.
Leap seconds function similarly to the leap days that we add to the end of February every four years to compensate for the fact that Earth orbits the Sun in 365.25 days. However, unlike leap years, which occur on a regular basis every four years, leap seconds are unpredictable.
The International Earth Rotation and Reference Systems Service monitors the speed of the planet’s rotation by sending laser beams to satellites to measure their movement, among other methods.
When the time plotted by Earth’s movement approaches one second out of sync with the time measured by atomic clocks, scientists all over the world coordinate to stop atomic clocks for one second, at 11:59:59 pm on June 30 or December 31, to allow astronomical clocks to catch up. There you have it — a leap second.
Since the first leap second was added in 1972, scientists have added leap seconds every few years. They’re added irregularly because Earth’s rotation is erratic, with intermittent periods of speeding up and slowing down that interrupt the planet’s millions-of-years-long gradual slowdown.
“The rotation rate of Earth is a complicated business. It has to do with exchange of angular momentum between Earth and the atmosphere and the effects of the ocean and the effect of the moon,” Levine says. “You’re not able to predict what’s going to happen very far in the future.”
But in the past decade or so, Earth’s rotational slowdown has … well, slowed down. There hasn’t been a leap second added since 2016, and our planet is currently spinning faster than it has in half a century. Scientists aren’t sure why.
“This lack of the need for leap seconds was not predicted,” Levine says. “The assumption was, in fact, that Earth would continue to slow down and leap seconds would continue to be needed. And so this effect, this result, is very surprising.”
The trouble with leap seconds
Depending on how much Earth’s rotations speed up and how long that trend continues, scientists might have to take action. “There is this concern at the moment that if Earth’s rotation rate increases further that we might need to have what’s called a negative leap second,” Whibberley says. “In other words, instead of inserting an extra second to allow Earth to catch up, we have to take out a second from the atomic timescale to bring it back into state with Earth.”
But a negative leap second would present scientists with a whole new set of challenges. “There’s never been a negative leap second before and the concern is that software that would have to handle that has never been tested operationally before,” Whibberley adds.
Whether a regular leap second or a negative leap second is called for, in fact, these tiny changes can be a massive headache for industries ranging from telecommunications to navigation systems. That’s because leap seconds meddle with time in a way that computers aren’t prepared to handle.
“The primary backbone of the internet is that time is continuous,” Levine says. When there’s not a steady, continuous feed of information, things fall apart. Repeating a second or skipping over it trips up the whole system and can cause gaps in what’s supposed to be a steady stream of data. Leap seconds also present a challenge for the financial industry, where each transaction must have its own unique time stamp — a potential problem when that 23:59:59 second repeats itself.
Some companies have sought out their own solutions to leap seconds, like the Google smear. Instead of stopping the clock to let Earth catch up with atomic time, Google makes each second a tiny bit longer on a leap second day. “That’s a way of doing it,” Levine says, “but that doesn’t agree with the international standard for how time is defined.”
Time as a tool
In the grand scheme of things, though, we’re talking about very tiny amounts of time — just one second every couple of years. You’ve lived through plenty of leap seconds and probably weren’t even aware of them. And if we view time as a tool to measure things we see in the world around us, like the transition from one day to the next, then there’s an argument to be made for following the time set by the movement of Earth rather than the electrons in an atomic clock — no matter how precise they might be.
Levine says he thinks that leap seconds might not be worth the trouble they cause: “My private opinion is that the cure is worse than the disease.” If we stopped adjusting our clocks to account for leap seconds, it could take a century to get even a minute off from the “true” time recorded by atomic clocks.
Still, he concedes that while it’s true that time is just a construct, a decidedly human attempt to make sense of our experiences in a big, weird universe, “it’s also true that you have the idea that at 12 o’clock noon, the Sun is overhead. And so you, although you don’t think about it often, do have a link to astronomical time.” Leap seconds are just a tiny, nearly invisible way of keeping that link alive.
Should we worried?
As yet, scientists are not entirely sure what is causing this increase in Earth’s rotation rate, but some have suggested it could be due to the melting of glaciers during the 20th Century, or the accumulation of large quantities of water in northern hemisphere reservoirs. However, experts predict that this speeding up is a temporary effect and the Earth will start slowing down again in the future.
But, for now, should we be worried? Although it will have no effect on our daily lives, there could be serious implications for technology such as GPS satellites, smartphones, computers and communication networks, all of which rely on extremely accurate timing systems. But such problems are ultimately surmountable, perhaps simply by subtracting a leap second rather than adding one.
So no, we shouldn’t be worried – unless the shortening of the day is attributable to human activity.