Why 2021 Was the Quickest Year Ever on Record

If 2021 seemed to go past in a blur, atomic clocks agree—the year was faster than usual.

New Year's Eve is often a time for people to reflect on the past 12 months, and while some may say the year felt as if it flew by, for others perhaps it seemed that time crawled along at a snail's pace.

But according to experts at time zone company TimeAndDate, 2021 really was, objectively, a shorter year than usual. That said, no humans could possibly have noticed.

Graham Jones, a science communicator at the company, told Newsweek that the past year has been approximately 65 milliseconds shorter than average—"the new shortest year on record."

It's all because of Earth's rotational speed. A small shift in how fast the planet spins might cause a day to be a tiny fraction of a second longer or shorter than its 86,400-second average.

"If you look at the length of a day, throughout the year, you can kind of see peaks and troughs," Graham said. "And one of the key things that affects that is the moon's orbit and the moon's distance from the Earth."

This is a relatively short-term effect, said Graham, but other factors like the sloshing of our planet's oceans and the movement of its interior are also thought to have an effect in the longer term—it's just not perfectly understood how. As such, it's difficult to make predictions about the Earth's rotational speed more than about six months in advance.

In general, it's thought that the Earth has been slowing down over long periods of time, causing years to get gradually longer, Graham added. This can be inferred from things like geological records or astronomical observations of solar eclipses.

"What was interesting last year is that we saw that the Earth kind of put on a burst of speed during the year," Graham said. "The acceleration of the speed has slowed down, but the Earth has still carried over its speed from last year, so this year is coming in quicker. The current thinking is that next year will be slightly shorter still, but it's difficult to say for sure."

Decisions on Leap Seconds

Official figures on the length of a day are published by the International Earth Rotation Office (IERS)—the same group that makes decisions on leap seconds if the Earth's rotational speed gets too far ahead of, or behind, schedule.

Since the 1960s, scientists have measured the length of a day using atomic clocks—astonishingly accurate clocks that don't lose or gain time more than about 0.0000001 seconds per year compared with an imaginary perfect clock.

Thanks to atomic clocks, scientists know exactly when the length of a day deviates from average.

"When atomic time was internationally adopted in 1967, the atomic clocks were 100 times more stable than a solar year," Kurt Gibble, an atomic clock expert and professor of physics at the Pennsylvania State University, told Newsweek. "In the past 30 years, atomic clocks have further improved by a factor of a million!

"Today's atomic clocks can precisely test our understanding of fundamental physics, ensure secure financial transactions, and easily provide the required timing, accurate to a billionth of a second, for mapping systems using the Global Positioning System GPS to guide our cars to virtually any address on Earth."

Looking back at speedy 2021, Newsweek has compiled a list of the best scientific discoveries and breakthroughs of the year.

Hourglass on beach
A file photo shows an hourglass on a beach. 2021 is thought to have been the quickest year as measured by atomic clocks. travellinglight/Getty