Scientists will abolish leap seconds when measuring time
International experts have decided to change the rules for counting world time. Adjusting the clock by one second, which has been used for decades to align atomic time with the Earth's rotation, has created problems for computer systems and other infrastructure. Instead, they plan to allow for a more significant discrepancy between the two frames of reference. About why scientists decided to abandon leap seconds and how this will change the measurement of time — in the material of Izvestia.
International Time Change Decision
The participants of the General Conference on Weights and Measures (CGPM) on October 15 approved the abandonment of the practice of adding leap seconds. The new rules are due to come into force on May 20, 2027. The solution will increase the allowable discrepancy between the coordinated universal time and the time determined by the Earth's rotation from a fraction of a second to one hour.
According to a publication in Scientific American magazine, this is not about abolishing the usual clocks and time zones, but about changing the principle of matching the two time measurement systems.
Coordinated Universal Time (UTC) is based on atomic clock readings, which provide an exceptionally stable countdown of seconds. Astronomical time is related to the rotation of our planet, the speed of which is constantly changing.
In 2022, representatives of the countries have already agreed to abandon the mandatory time adjustment by one second no later than 2035. However, in recent years, experts have begun to consider the possibility of accelerating the transition. The reason is the risk that due to the acceleration of the Earth's rotation, for the first time it will be necessary not to add, but to remove a second. For computer systems, such a scenario can be particularly difficult.
Why were leap seconds needed?
The leap second was introduced in 1972. Its task is not to allow atomic time to diverge too much from astronomical time. Atomic clocks count time according to the physical processes inside atoms, whereas the length of a day depends on how long it takes the Earth to rotate around its axis.
The rotation of the planet does not remain unchanged: it is influenced by various processes inside the Earth and interaction with the Moon. In the long run, the rotation slows down, although the speed may increase over shorter periods. Therefore, the astronomical day does not always correspond exactly to the 24 hours counted by the atomic clock.
To maintain the consistency of the two systems, experts periodically added a second to the universal time. Since 1972, such an adjustment has been carried out 27 times. The last leap second was added on December 31, 2016.
The problem is that the need for adjustments depends on the actual rotation of the Earth and is not determined in advance by a fixed schedule. The situation became more complicated after the planet's rotation began to accelerate from about 2015. As a result, scientists began to consider the possibility of a negative leap second — that is, a change in which the clock would have to skip a second rather than add it.
Patricia Tavella, Director of the Time Department at the International Bureau of Weights and Measures
We calculated that if we wait until 2035, the risk of a negative leap second will be 30%.
According to her, experts discussed this risk with users and organizations who care about the exact time, and found that even a 10% probability raises serious concerns.
Why does the one-second adjustment create problems?
Leap seconds are necessary to coordinate time, but adding them breaks the continuous sequence on which many digital systems are built. Computers, telecommunication networks, financial platforms, and energy infrastructure use synchronized clocks to record events and correctly order transactions. An unexpected time change requires special software handling.
It is noted that the previous leap seconds have already been accompanied by failures from technology companies, including Meta (recognized as extremist and banned in Russia), Reddit and Cloudflare. The adjustments also created difficulties for aviation and high-frequency exchange trading. As digital infrastructure becomes increasingly dependent on accurate synchronization, even a small change in time can become a source of technical risks.
An additional problem is the lack of a single way to handle leap seconds. Some systems add it at a specific moment, resulting in a 61-second minute. Other companies distribute the adjustment over a longer period, gradually changing the clock. This approach, known as "blurring" seconds, is used, for example, by Google. Different methods can create discrepancies between time sources.
Georgette McDonald, CEO of the Halifax Metrological Research Center
We're getting a gap in a system that should be running continuously.
As a result, avoiding regular second adjustments should reduce the likelihood of such failures and simplify the operation of systems that require a stable time frame.
What will change after the abandonment of leap seconds
Instead of frequent small adjustments, it is proposed to allow the difference between coordinated universal time and astronomical time to increase to one hour. This approach is sometimes referred to as the leap second to leap hour transition.
This does not mean that in 2027 everyone will have to move their clocks forward or backward by an hour: the change concerns the permissible discrepancy between time measurement systems, not the daily schedule.
According to experts, with this approach, the need for large-scale adjustments may arise only after hundreds or even thousands of years. During this time, digital systems and ways of measuring time can change significantly. At the same time, scientists who are engaged in astronomy and geodesy will still need to take into account the difference between atomic time and the rotation of the Earth.
There is also a conceptual side to the transition. For thousands of years, people have correlated time with the movement of celestial bodies and the alternation of day and night. Atomic clocks made it possible to measure seconds much more stably, but the need to coordinate their readings with the rotation of the planet persisted. The new solution means that for the sake of the reliability of the digital infrastructure, humanity is ready to allow a more noticeable discrepancy between these systems.
At the same time, the rejection of leap seconds does not eliminate the need to measure the rotation of the Earth and take it into account in scientific calculations. It changes exactly the rules for maintaining universal time: instead of regular one-second adjustments, systems will be able to operate at a more stable standard, and the difference with astronomical time will be taken into account separately.
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