The leap second’s time will be up in 2035—and tech companies are thrilled
This is the last countdown for leap second ,. It’s a janky method of aligning atomic clock with natural variation in the Earth’s rotation. But we’ll get there. At a meeting last week in Versailles, the International Bureau of Weights and Measures (BIPM) voted nearly unanimously to abandon the controversial convention in 2035 for at least 100 years. The world’s metrologists, people who study measurement, are hoping for a better solution to sync human timekeeping with the natural world. Here are the reasons it matters.
Unfortunately, the universe is messy for us humans. While approximate values are useful for daily life, they don’t suffice for advanced technology or scientific measurements. Take years: Each one is 365 days long, right? Well, not quite. It actually takes the Earth something like 365. 25 days to rotate around the sun. That’s why approximately every fourth year (except for years evenly divisible by 100 but not by 400) is 366 days long. Our calendar is roughly aligned to the Earth’s actual rotation by adding a leap day.
Things get more frustrating the more precise you try to measure them. A day is 86,400 seconds long–give or take a few milliseconds. The Earth’s rotation is actually slowing . This is due to many complicated factors such as the ocean tides, shifts in the Earth’s mass distribution, and more. All of this means that days are becoming ever more long, just a few milliseconds at time. If we continued to assume that all days are exactly 86,400 seconds long, our clocks would drift out of alignment with the sun. If you wait long enough, it will start rising at midnight.
In 1972, BIMP (it comes from the French name, Bureau International des Poids et Mesures) agreed to a simple fix: leap seconds. Leap seconds, like leap days, would be inserted into a year to align Universal Coordinated Time(UTC) and Earth-tracking Universal Time [UTI]. Leap seconds don’t come along very often or predictably. Instead of creating a pattern for adding them, BIMP would add up all the extra milliseconds. If necessary, it would tell everyone to add one millisecond to UTC. Between 1972 and now, 27 leap seconds have been inserted into UTC.
While probably not the best idea even back in the 70s, the leap second has become a progressively worse idea as computers made precision timekeeping more widespread. The creation of the leap second was not possible without precise clocks. These clocks were only available to military installations and research laboratories at the time. Now, every smartphone can get the exact UTC time accurate to 100 billionth of a second from the GPS and other navigation satellites in orbit.
The problem is that all interconnected computers on the internet use UTC to work, not just to let you know it’s lunch time. Files are saved to a database and time stamped with UTC. Online games rely on UTC to determine who shot first. If you tweet, UTC is included in the mix. Keeping everything on track is a major headache for large tech companies like Meta–which recently published a blog post calling for the abolition of the leap second–that rely on UTC to keep their servers in sync and operational.
This is because the process of adding leap second–or possibly removing it as the earth appears to be speeding back up for some reason –break key assumptions computers have about time. These are simple rules: Minutes have 60 seconds, time always goes forward, doesn’t repeat, doesn’t stop, and so on. It is very easy for two computers meant to be in sync, to get out of sync by inserting and removing leap seconds. And when that happens things can break.
When a leap second was added in 2012, Reddit went down for 40 minutes. DNS provider Cloudflare had an outage on New Year’s Day in 2017 when the most recent leap second was added. These occurred despite the best efforts by the companies to account for the leap second, and mitigate any adverse consequences.
Large companies have developed techniques such as “smearing,” which allows the leap second to be added over time rather than being done all at once. It would be much easier if they didn’t have to.
This brings us back to the important decision made last Friday. From 2035, leap seconds are no longer going to matter. BIMP is going to allow UTC and UTI to drift apart until at least 2135, hoping that scientists can come up with a better system of accounting for lost time–or computers can get smarter about handling clock changes. Although it’s not an ideal solution, it may be easier to fix than many modern problems.
I’m a journalist who specializes in investigative reporting and writing. I have written for the New York Times and other publications.