but it was actually the shortest year in decades.

In fact, it was 1.3 milliseconds shorter.

The planet is now spinning faster than it has any time in the last half-century,

with 2020 containing 28 of the fastest days on record since 1960.

And 2021 is expected to be even faster...

which has ignited a fiery debate about what we should do to keep the world on track.

It may sound weird, but shifts in a planet's spin are actually normal.

Things like the pull of the moon,

jet stream winds,

and plate tectonics all have an effect.

Just like an ice skater draws in their arms to spin faster,

anything that moves mass closer to Earth's axis speeds up the planet's spin,

making the days a few milliseconds shorter.

It doesn't seem like much, but these subtle changes in Earth's spin

can cause major headaches for anyone trying to keep their clocks in sync.

But first, here's a little context on how our timekeeping has evolved.

Before we had cell phones, computers, or GPS to tell time, we had the Sun.

Ancient civilizations measured time using Earth's rotation relative to the sun

with devices like sundials.

We know this today as solar time.

Around 150 AD, Ptolemy divided Earth's 360 degrees of latitude and longitude

into 60 equal parts, into the “first minute”, and then again, into a “second minute”, the basis for a second.

The development of quartz clocks in the 1930's made timekeeping even more precise,

and for the first time allowed us to measure variations in Earth's rotation.

Then atomic clocks revolutionized timekeeping.

In 1955, the National Physics Laboratory in England built the first accurate cesium clock,

and twelve years later, the General Conference on Weights and Measures redefined the second,

based on this crazy number of oscillations of a cesium atom.

This ultra-precise definition of a second is the foundation of International Atomic Time,

the average of hundreds of atomic clocks worldwide, making it our most accurate time keeper.

Atomic time can measure the spin of the planet down to the millisecond.

But the increase in accuracy comes with a downside.

Since atomic time ticks away at an incredibly constant rate,

it doesn't slow-down or speed-up with the spin of the Earth.

So, over the years atomic time has slowly drifted out of sync with the fluctuations of the planet.

Whenever the difference between solar time and atomic time

threatens to exceed 0.9 seconds,

a leap second gets added to Coordinated Universal Time to make up for the difference.

UTC is kept using atomic clocks, but with all those leap seconds added in.

To date, we've added 27 leap seconds since 1972.

The extra second gets squeezed in at midnight UTC.

Which is where the heated debate comes in.

Those who want to abolish the leap second say that in addition to being cumbersome,

it would take 5,000 years to notice even a one hour difference

between Earth's rotation and the atomic clock.

And when one was added in 2012,

the reservation system used by Qantas airlines collapsed,

and several websites including Reddit, Mozilla, and Gawker,

crashed when their systems failed to handle the extra second.

However, those in favor of the leap second argue that the technical issues are overblown.

Just a few years later in 2015, another second was added—

and there were only a few minor hiccups.

The standoff is real and countries have already taken sides,

with the U.K. and Russia in favor of keeping leap seconds,

and countries like the U.S. and China advocating their drop.

At the 2015 World Radiocommunication Conference held by the U.N.,

countries couldn't come to an agreement,

so they decided to put off their decision till their next conference in 2023.

But no matter how long they debate, the Earth will continue to spin.

And it's up to the International Earth Rotation and Reference Systems Service, or IERS,

to determine if a year needs a leap second or not.

Last year Earth's rotation was fast,

and didn't need a leap second—at least, in the traditional sense.

Because it was spinning so fast,

the average day was estimated to be .05 milliseconds shorter than a typical 24-hour period.

Because of this, the group considered something they never had before: adding a negative leap second.

Instead of gaining a second, we would lose one.

And this year, scientists expect it to be even speedier!

While the group ultimately decided not to add this negative leap second last year,

it's possible that they might have to when they meet again this June.

All I know is when they finally make a decision,

we'll all be saying, it's about time.

We talked about removing a second from our clocks, but what about time itself?

Can it ever run backward?

Check out this video from Julian that explains how time might not reverse like physicists thought.

Have some cool science you'd like to see us cover?

Let us know in the comments below and as always, thanks for watching Seeker.