Near Versailles this week, the keepers of global time gather to decide whether humanity will stop bending the clock to match the Earth's imperfect spin. Since 1972, scientists have inserted 27 leap seconds into Coordinated Universal Time to reconcile the precision of atomic clocks with the wobbling rotation of our planet — a quiet, recurring intervention that has grown increasingly costly in an age of networked systems. The vote by the International Bureau of Weights and Measures reflects a deeper tension as old as civilization: the desire to stay tethered to the natural world, weighed against
BIPM to vote on ending leap seconds, proposing 'leap hour' alternative
Time would have to jump forward by one second—something never tested before.
Mark
So the BIPM is voting on whether to stop adding leap seconds. Why does that matter to anyone outside of timekeeping specialists?
Mimi
Because leap seconds break things. When one is added, computer systems that assume time only moves forward in 60-second increments suddenly encounter a 61st second. It's caused outages at major internet companies.
Luke
But how often does that actually happen? Twenty-seven times in fifty years—that's roughly every two years. Is that really enough disruption to warrant changing a system that's worked since 1972?
Mimi
The disruption is real, but you're right that it's infrequent. The bigger problem is the unpredictability. Leap seconds are announced only six months ahead, and now there's a risk of a negative leap second—something that's never happened and software has never been tested for.
Mark
A negative leap second? What does that mean?
Mimi
Instead of adding a second, time would jump forward by one. It's the opposite of what we've done for fifty years. No one knows how systems will respond.
Luke
So this is partly about a theoretical risk that hasn't materialized yet, combined with the real but infrequent disruptions we've seen.
Mimi
Yes. And the solution they're proposing is to let UTC drift from Earth's actual rotation until the difference reaches a full hour, then make one massive adjustment.
Mark
In how long?
Mimi
More than a thousand years. Earth is losing less than one second per year.
Luke
So we're solving a problem that happens every couple of years by creating a problem that won't happen for a millennium. That's a trade-off worth examining.
Mark
What happens if the vote doesn't pass?
Mimi
The current system continues, with all its disruptions and the looming risk of something untested happening.
Il Polso
- Earth's rotation has begun accelerating, raising the specter of a negative leap second — a scenario no software on the planet has ever been designed to handle.
- Each of the 27 leap seconds added since 1972 has been a quiet crisis: Cloudflare went dark, Reddit collapsed, and engineers spent hours hunting bugs born from a single rogue second.
- The BIPM, which had already set a 2035 deadline to retire leap seconds, is now under pressure to move faster before an unprecedented negative correction triggers cascading failures across global infrastructure.
- The proposed resolution is a kind of civilizational patience — let UTC drift freely from solar time, accumulate the difference over centuries, and settle the debt with a single 'leap hour' adjustment more than a thousand years from now.
- The vote near Versailles will determine whether the world trades the small, disruptive corrections of the present for one enormous, distant reckoning — a bargain struck today for a problem no one alive will witness.
Near Versailles this week, the keepers of global time gather to decide whether humanity will stop bending the clock to match the Earth's imperfect spin. Since 1972, scientists have inserted 27 leap seconds into Coordinated Universal Time to reconcile the precision of atomic clocks with the wobbling rotation of our planet — a quiet, recurring intervention that has grown increasingly costly in an age of networked systems. The vote by the International Bureau of Weights and Measures reflects a deeper tension as old as civilization: the desire to stay tethered to the natural world, weighed against the demands of the artificial one we have built atop it.
In a conference room near Versailles, an obscure but consequential vote is unfolding. The International Bureau of Weights and Measures — the body entrusted with global timekeeping — is deciding whether to end a practice that has quietly shaped our measurement of seconds for more than fifty years.
The issue begins with a fundamental mismatch. Atomic clocks tick with absolute regularity, but Earth does not rotate at a constant speed. The planet's spin is gradually slowing under the Moon's gravitational influence, and to keep official time aligned with the actual position of the sun, scientists have periodically inserted single seconds into Coordinated Universal Time. This has happened 27 times since 1972, most recently in 2016.
For the digital world, each of those seconds has been a small catastrophe waiting to happen. Computer systems are built on the silent assumption that a minute always contains exactly 60 seconds. A leap second breaks that assumption, and the consequences have been tangible: Cloudflare suffered outages, Reddit went down, and platforms spent hours diagnosing failures born from a single extra tick of the clock. Leap seconds are announced only six months in advance, leaving little time for engineers to prepare.
What has sharpened the urgency is something entirely new. Earth's rotation has been accelerating since around 2020, and scientists now face the possibility of a negative leap second — time jumping forward rather than back. No system has ever been tested for this. The prospect prompted the BIPM to accelerate its timeline, having already voted in 2022 to phase out leap seconds by 2035.
The solution on the table is to stop compensating for Earth's drift at all. UTC would be allowed to wander gradually away from solar time, accumulating the gap second by second. Only when the difference reaches a full hour would a single correction be made — and given the pace of Earth's slowdown, that moment is more than a thousand years away. The vote near Versailles is, in essence, a decision to trade small recurring disruptions today for one distant, enormous reckoning that no one now living will ever see.
This week, in a conference room near Versailles, an obscure but consequential vote will take place. The International Bureau of Weights and Measures—the global body that keeps time itself—will decide whether to end a practice that has shaped how we measure seconds for more than half a century. The question sounds technical. The answer will ripple through every system that depends on precision: satellites, financial networks, the infrastructure of the internet itself.
Since 1972, leap seconds have been inserted into Coordinated Universal Time, the atomic standard that governs global timekeeping. The reason is elegantly simple: Earth does not rotate at a constant speed. The planet's spin is gradually slowing, influenced by the Moon's gravitational pull and other forces. Atomic clocks, by contrast, tick with metronomic precision. To keep UTC aligned with the actual rotation of the Earth—to ensure that noon stays roughly when the sun is highest—scientists have periodically added single seconds to the clock. Over fifty years, this has happened 27 times, most recently at the end of 2016.
But those 27 leap seconds have become a persistent headache for the digital world. Computer systems are built on an assumption so fundamental that it is almost never stated: time moves forward, and a minute always contains exactly 60 seconds. When a leap second arrives, that assumption breaks. Software does not know what to do with a 61st second. The consequences have been real. Cloudflare, one of the world's largest internet infrastructure companies, experienced outages. Reddit went down. Other platforms suffered glitches that took hours to diagnose and repair. The problem is compounded by the fact that leap seconds are announced only six months in advance, giving software developers limited time to prepare.
What makes the current moment urgent is something that has never happened before. Earth's rotation has been accelerating since around 2020, and scientists now face the possibility of a negative leap second—a moment when time would have to jump forward by a full second rather than backward. No software has ever been tested for this scenario. The prospect of this unprecedented event prompted the BIPM to accelerate its timeline. In 2022, the body had decided to phase out leap seconds by 2035. Now, with the vote this week, that deadline may move closer.
The proposed solution is elegant in its own way: stop fighting Earth's rotation. Instead, allow UTC to gradually drift away from solar time, accumulating the difference second by second, year by year. When the gap reaches one hour, a single "leap hour" adjustment would be made. Because Earth is losing less than one second per year, this correction would not be necessary for more than a thousand years. By then, the systems we build today will be archaeological artifacts. The vote near Versailles will decide whether to accept this bargain: one massive adjustment in the distant future, in exchange for stability and predictability now.
Citazioni salienti
Leap seconds create difficulties for computer systems because software assumes time only moves forward and a minute always has 60 seconds.— Technical challenges cited by BIPM
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