The leap second lives on borrowed time before the vote in Versailles

The world’s time lords are in Paris this week to make a decision that could change the very nature of time.

Members of the International Bureau of Weights and Measures (BIPM), including Australia’s own chief metrologist, will determine the future of what they call a leap second.

While most people understand the concept of leap years – an extra day every four years to ensure our calendar stays connected to the actual period it takes Earth to orbit the sun – the idea of ​​a second intercalary is more esoteric.

Unlike leap years, which occur every four years, leap seconds can vary. It all depends on the rotation of the earth.Credit:Fairfax Media

Since 1972, a leap second has been added 27 times to the world’s time systems.

The leap second is a consequence of two factors; the daily rotation of the earth varies by exact 24 hours, and huge advances in the precision with which we measure time.

Measuring time

The world didn’t really have an accurate measurement of the second until 1657, when Dutch mathematician, physicist, and astronomer Christiaan Huygens invented the pendulum clock.

Until now, it was extremely difficult to accurately measure a second (minute hands on clocks were not invented until the end of the 16th century, with seconds hands coming about 100 years later).

Huygens – one of history’s greatest scientists who discovered Saturn’s rings, introduced mathematics to physics, and made substantial breakthroughs in everything from game theory to the use of algebra – created a type of clock that would efficiently and accurately set time for the next 300 years.

In terms of accuracy, pendulum clocks were superseded when Warren Marrison, working for Bell Laboratories in the United States in the 1920s, discovered that a small burst of electricity through a piece of quartz delivered a constant pulse .

This pulse was so constant that it meant that quartz clocks were significantly more accurate than pendulum clocks.

But in the 1950s, another milestone in precision was taken with the creation of the first atomic clocks.

Instead of quartz, the radiation produced from two hyper-fine ground pieces of the mineral cesium was found to have a frequency that delivered what at the time was considered a perfect second.

The official definition of a second, adopted in the early 1960s, is “the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium-133 atom”.

For most of human history, time was local. Communities had their own municipal clocks that set the time according to sunrise and sunset. International time zones were not formalized until the 1880s.

Atomic Time vs Astronomical Time

The rise of atomic time meant a conflict with astronomical time.

The decision to include an extra second every few years – the leap second – was made to ensure that atomic and astronomical time did not get out of whack.

Dr Michael Wouters, a researcher at Australia’s National Measurement Institute, explains that creating the leap second was seen as a simple way to solve a small problem.

The problem is that since the first leap second in 1972, the world has actually become one huge interconnected computer system.

And messing with time, even adding a second here or there, creates problems.

“Doing a jump a second time is a problem,” he says.

Panic posts

US-based Cloudflare is a content delivery network that also helps prevent distributed denial of service attacks when a targeted website is overwhelmed with fake traffic.

When the last leap second was added to global time systems in 2016, Cloudflare’s Domain Name System (DNS) went negative and began to “freak out”, causing a small number of web properties to fail. managed by the company. The issue took about 90 minutes to resolve.

“The root cause of the bug that affected our DNS service was the belief that time cannot be turned back,” John Graham-Cumming of Cloudflare reported in 2017.

Four years earlier, Reddit (among others) had dropped to 30-40 minutes due to the 2012 leap second.

The BIPM notes that global navigation satellite systems, telecommunication networks and power transmission systems could all fail unexpectedly due to the inclusion of a leap second.

But not having a really accurate time can be even worse.

Is the juice worth it?

For an organization like NASA, time is a distance. The US space agency notes that a quartz clock is not stable enough for space travel.

After an hour, the most efficient quartz clock can be exceeded by a billionth of a second. After six weeks, he estimates that such a clock could be overtaken by a full millisecond.

The fastest hummingbirds can flap their wings about five times in a millisecond. But in space, that millisecond can be about 300 kilometers away.

The Orion capsule atop NASA’s Space Launch System rocket is supposed to fly within 100 kilometers of the moon’s surface. The agency needs a precise time so they can track Orion on his vital journey.

Ahmad Byagowi is a California-based research scientist at Meta who specializes in areas such as time and frequency synchronization in large networks.


He says a leap second is, in theory, a simple way to compensate for the Earth’s irregular rotation.

“What is causing the problem is our quest for faster and more powerful computers as well as our dependencies on precision time for various things like navigation (aircraft and railroads), distribution of energy, data centers, etc.,” he said in an email.

“As we become more dependent, our vulnerability increases, leading to disruptions and outages. It would be nice if we had a common system to follow on how to apply leap seconds or how to predict when it is needed in the future, but even if we did, the questions arise – why and what is the advantage of doing it, if the juice is not worth it?

Byagowi says that if leap seconds were discontinued as predicted, it would take about 1,000 years before there was a noticeable discrepancy between the relative position of stars in the sky and the time of the atomic clock.

“We started observing Earth’s rotation only about 50 years ago with the atomic clock,” he said.

“For the foreseeable future, Meta engineers are supporting a larger community to stop future introduction of leap seconds and stay at the current level of 27, which we believe will be sufficient for the next millennium.”

The notion of temporal slowing down is difficult to conceive.

When dinosaurs roamed the earth, they had less than 23 hours a day. The gravitational fight between the Moon and the Earth was much more intense because the distance between them was much less than the current 384,000 kilometers.

If you were on Alexander the Great’s campaign in India in 327 BC. AD, and able to measure time accurately, you would have noticed that an hour was a minute or two longer than it is today.

It is therefore not surprising that the debate over the future of the leap second has dragged on for 20 years.

Vote on a 100-year break

The actual motion that will be discussed in Paris is to begin a 100-year hiatus on new leap seconds from 2035.

“The measurement community doesn’t make decisions very quickly,” notes Wouters dryly.

Michael Wouters with the Australian Atomic Clock.Credit:Ben Rushton

According to the proposal, any additional leap seconds would be added over the next 12 years. Beyond that, scientists would have at least a century to find a new way to reconcile atomic time with astronomical time.

If there is no solution, the difference between atomic time and astronomical time by 2135 would be about one minute. Instead of a leap second, scientists in the next century should consider adding a full minute to the time system.

Australia’s chief metrologist Bruce Warrington, who is also the chief executive of the National Institute of Measurement, said from Paris that Australia would support ending the second jump.

“Our position is based on technical advice and we are in good company with other countries that share this position,” he said.

“We will work with international partners and consult with the Australian community as appropriate throughout this process.”

Unlike leap years, which occur every four years, leap seconds can vary. The last one was in 2016 but there was one added every year between 1992 and 1995. It all depends on the rotation of the earth.

Melting and refreezing of the world’s mountains, shifting tectonic plates and possibly even climate change have meant that some analysts have detected a slight increase in Earth’s rotational speed over the past two years.

If this continues, instead of adding a leap second, the world might have to lose a leap second.

Byagowi warns that having a second one-day outage could cause even bigger problems in our IT world.

“If we decide not to abandon the practice of the leap second, we will soon have to add a negative leap second,” he said.


“This has never been verified on a large scale and will likely lead to unpredictable and devastating outages across the world.”

The future of the leap second isn’t the only topic of discussion in Paris. The very definition of a second is the order of the day.

The definition of cesium radiation of one second in use for almost 60 years is likely to end. Advances in precision and technology mean that the BIPM 2026 conference will discuss a replacement, with the aim of having it adopted when it meets in 2030.

Time, even a second, does not stop.

Cut through the noise of federal politics with news, opinion and expert analysis from Jacqueline Maley. Subscribers can sign up for our weekly Inside Politics newsletter here.

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