On October 15, 2026, during the 28th General Conference on Weights and Measures, the Meter Convention decided to eliminate the use of leap seconds, which had served as a patch since 1972 to equate astronomical time with atomic clocks. As a result, both measurements will differ freely as long as they are located one hour apart. At that point, measures can be taken to equalize them. It is estimated that this will happen hundreds of years from now, so for now we can rest easy and flow with the times. According to metro convention, this is best for our computer system.
End of an era. Since 1972, 27 leap seconds have been added to the atomic clocks to synchronize them with the Earth’s rotation. The goal was to have a difference of no more than 0.9 seconds between astronomical time (UT1) and UTC. However, this decision was withdrawn after the meeting of the member countries of the Metro Convention. Only Russia voted against, so the measure will go ahead and become continuous UTC from May 20, 2027, it will not be adjusted anytime soon. This will continue until there is an hour difference.
Two ways to measure time. Until the 1960s, the latter measured 1/86,400 of a mean solar day. Then, until 1967, it was considered a fraction of the tropical year of 1900. However, the Earth’s rotation is not an exact science. We say that it takes 24 hours to make a revolution; But, to begin with, the exact figures are not. In reality, a sidereal day lasts 23 hours, 56 minutes and 4 seconds, slightly different from a solar day. And solar isn’t entirely accurate either, since the Earth’s rotation fluctuates, causing it to speed up or slow down.
For this reason, in 1967 it was decided to base the measurement of time on something as accurate as the physics of atoms. They were looking for something that would take about a second and chose 9,192,631,770 periods of radiation to transition between two hyperfine levels of the ground state of cesium-133. Clocks that measure time based on this standard are known as atomic clocks, but UTC time comes from not just one, but an average of 450 atomic clocks located in 85 laboratories in different countries.
Second break? Since UTC time is accurate and UT1 fluctuates due to the acceleration or deceleration of the Earth, it was decided in 1972 to add a leap second if necessary to synchronize both times as much as possible. Of course, there is no exact time to add them. It all depends on how the imbalance progresses.
Every 6 months the International Earth Rotation and Reference System Service (IERS) publishes a report, called Bulletin C, that indicates whether to add a leap second, based on how UTC time has moved away from UT1 over the past half year. Leap seconds are usually added in June or December, and on average one is added every year and a half.
Be careful with electronic systems. There are several factors that affect the speed of the Earth’s rotation. Some are natural, such as tides and the movement of elements at Earth’s center, and others are artificial. It has been found that even filling the Three Gorges in China can affect the Earth’s rotation. Furthermore, we cannot forget the causes caused by climate change, such as the melting of the polar ice caps. This changes the Earth’s mass distribution, as some of the weight of the polar ice is distributed throughout the oceans. Some of these factors accelerate turnover, while others slow it down. But, on the whole, it may soon be necessary to add a second negative. It is estimated that there is a 30% chance that this will happen before 2035.
Computer systems calculate time based on atomic clocks, but they are not ready to go back, so this decision will affect them significantly. Since most of what we do in our daily lives is connected to a computer system, chaos can be unleashed. That’s why we chose to abandon leap seconds and flow.
Isn’t an hour too much? At first, there won’t be much difference from making this decision. However, when we go from seconds to minutes and dangerously close to hours, experts believe that problems may arise. While others don’t believe it. Opinions are quite divided.
UTC time is calculated using 450 atomic clocks distributed around the world. Credit: Shujianyang
in favor of Felicitas Arias, former Director of the BIPM Time Department, explained in the collected statement. Scientific American Something similar happens during that seasonal change. In most countries the jump of an hour between summer and winter is much longer than a second, and it doesn’t affect us beyond being asleep for a few days. What he says, however, is the fact that there are also many scientists who have been warning about the health risks of time-shifting for some time. At most, it and other experts consider that, when the difference is large, countries can permanently move their legal time zones by one hour.
The consequences of which we cannot ignore. Arguments against this decision include those that indicate that astronomers, earth scientists, and other users of Earth orientation data must consider the incremental lag when relating their measurements to civil time. However, Elizabeth Donnelly, former director of NIST’s Time and Frequency Division, points out that astronomers already use methods that absorb the difference, so in principle this shouldn’t be a problem.
However, how to act when the difference is too large has yet to be determined. We’ve had hundreds or even thousands of years to think about it, so for now the scientists who made the decision seem pretty cool. Brown will be the turn of others.
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