What if one day lasted 25 hours? It sounds impossible today, but our descendants, about 1,000 years from now, could experience exactly that if a “leap hour” is ever introduced.
Scientists, diplomats, and timekeepers across the globe agreed to this idea at a conference in Paris Thursday.
At this year’s General Conference on Weights and Measures (CGPM), officials voted, by a sweeping majority, to end the practice of adding leap seconds. These conferences are hosted every four years by the International Bureau of Weights and Measures (BIPM) and discuss measurement issues with member states worldwide.
Leap second: why was it adopted
The system of inserting leap seconds was adopted as early as 1972 at the behest of scientists who noted that Earth’s rotation was slowing down. It was introduced to keep the world’s standard time reference synchronized with Earth’s rotation.
Coordinated Universal Time (UTC) is the world’s standard timescale, first established in 1960 to keep clocks in different countries and time zones aligned.
It is calculated as a weighted average of atomic clocks worldwide and is communicated by BIPM, the official source for UTC.
This standard time is critical, guiding how computers, phones, boats, planes, satellites, and everything else tell time. The Global Positioning System (GPS) also gets its time references from UTC.
Using this approach, scientists have managed to keep UTC aligned with UT1, time based on Earth’s rotation, within one second for nearly five decades, preventing world clocks from running amok.
Every few years, a leap second was added to the world clock to prevent the two from drifting too far apart. Since 1972, a total of 27 leap seconds have been added.
Earth spin pushing world backwards
In the mid-2010s, scientists noticed that Earth’s spin began speeding up. Perhaps as early as 2029, instead of adding a leap second, they may have to omit a second.
This has rattled the scientific community for years now.
Engineers said in a statement that a negative leap second would be like a “mini Y2K” event. It would suddenly push the world back by one second, causing chaos in our digital infrastructure.
To avoid negative leap seconds, scientists agreed to expand the leap-second window to a leap hour.
“Avoiding negative leap seconds is a very big driver to open the window” between UTC and UT1, said Nick Stamatakos, head of the Earth Orientation Department at the U.S. Naval Observatory, which manages the country’s GPS grid.
Instead of using leap seconds, everyone has agreed to tolerate more drift between UTC and UT1 than in the past. When things get really bad, they’ll add a leap hour instead, the scientists said.
Replacing leap seconds with a leap hour would extend the allowed difference between UT1 and UTC to 3,600 seconds, but scientists said that reality is still more than 1,000 years away.
Most of us won’t witness the change, as it would take nearly 25 generations of human life for the switch to continuous time. Until then, omitting leap seconds will make our digital infrastructure easier to manage and less prone to bugs or service outages arising from a leap second discontinuity.
The decision came after nearly three decades of debate.
“After 30 years of debates, we are ready,” said Noël Dimarcq, a senior scientist at the French National Center for Scientific Research (CNRS) and president of BIPM’s Consultative Committee for Time and Frequency, just before the vote.
They said this change will take effect next year, on World Metrology Day, which falls on May 20 every year, according to an article in Scientific American.