Temporary difficulties: how will earthlings survive the abolition of leap seconds

The timekeepers decided to forget about the extra, so-called leap second. On October 15, at the General Conference on Weights and Measures in Versailles, it was decided to cancel the extra moment. What kind of second it is, why it is needed, why it has lost its relevance and how its absence will affect the lives of ordinary earthlings — in the Izvestia article.

What is a leap second and why is it needed?

A leap second is an adjustment of Coordinated Universal Time (UTC) by one second, recalls Svyatoslav Litvinov, Candidate of Technical Sciences, Associate Professor of the Department of Radioelectronic Systems and Complexes at RTU MIREA. It appeared in 1972, when atomic clocks had already become the basis for accurate time counting, but it became necessary to keep UTC in touch with astronomical time, which is determined by the rotation of the Earth.

— An atomic second has a strictly defined duration, and the Earth does not rotate absolutely evenly: the speed of its rotation is influenced by processes in the atmosphere and oceans, the movement of masses inside the planet, and other factors. Therefore, the two scales are gradually diverging. When the difference between UTC and UT1 approaches 0.6 seconds, IERS can introduce an additional second to avoid exceeding the 0.9 second threshold," the specialist comments.

This does not happen after a certain number of years — the moment of correction depends on the actual rotation of the Earth, the Izvestia interlocutor notes. Since 1972, 27 positive leap seconds have been introduced (negative ones did not have to be taken into account). The last one was recorded on the night of January 1, 1917.

The leap second is not a matter of fundamental science or astronomy, but a purely applied, administrative decision related to time synchronization in high—precision instruments and communication systems, emphasizes Candidate of Physico-Mathematical Sciences, senior researcher at the Department of Theoretical Astrophysics and Cosmology of the Astrospectric Center of the FIAN (Physical Institute named after Lebedeva RAN) Elena Mikheeva.

— The Earth is gradually slowing down its rotation under the influence of the moon. It depends mainly on the tidal effect of the Moon on the Earth. Our natural satellite is gradually moving away from us. As a result, small discrepancies accumulate between atomic time and the actual rotation of the planet," the expert explains.

The abolition of the leap second is due to the fact that modern technologies allow for more accurate accounting of these microscopic deviations without introducing additional units of measurement. In everyday matters, such a difference is almost imperceptible, but for precision instruments and navigation systems, correction is important. If the devices are linked to the current time and their synchronicity is required, then appropriate corrections are made. Moreover, technologies are developing faster than noticeable deviations in time accumulate, the editorial interlocutor emphasizes.

How will the abandonment of leap seconds affect precision instruments

Svyatoslav Litvinov believes that the problem for modern digital infrastructure is not the abolition, but the introduction of leap seconds.

— Many information systems are designed for a continuously increasing time scale. The appearance of an unusual moment like 23:59:60 must be specifically handled programmatically. If different servers, network equipment, or programs do this in different ways, then timestamps become out of sync," explains the associate professor at RTU MIREA.

For telecommunication networks, energy systems, and distributed computing, precise timing is necessary, for example, to determine the sequence of events and synchronize equipment, he continues.

— An error doesn't even have to stop the entire system: it's enough for its different elements to get different ideas about the current time for a short time. As a result, incorrect event logs, data exchange errors, or software failures appear. The risk of failures prompted the abandonment of regular leap seconds: in 2022, CGPM decided to increase the allowable gap between UTC and UT1 in order to permanently eliminate such jumps, the expert points out.

Satellite navigation systems, he said, have already largely circumvented this problem. GPS, Galileo, and BeiDou use their own continuous time scales without regularly adding leap seconds, and the necessary connection to UTC is taken into account separately. This allows you not to interfere with jumps in the main countdown inside the system.

Skeptics believe that the transition to a continuous scale also requires a lot of technical and legislative efforts, so the abolition of the leap second could be delayed. One way or another, the meeting of the General Conference of the International Telecommunication Union (ITU), which has legislative power, will put an end to this historical process. It is scheduled for next year.

How will people react to the cancellation of an extra moment

The main task of the leap second was to ensure that civil time, based on extremely stable atomic clocks, did not noticeably diverge from the time associated with the rotation of the Earth, explains Svyatoslav Litvinov. This made it possible to keep UTC and astronomical time very close to each other for decades.

— In everyday life, a person hardly notices an extra second. Smartphones, computers, and other devices receive the exact time automatically, and most programs hide the correction process from the user. After the abandonment of regular leap seconds, household clocks will also not noticeably "run away" from the position of the Sun. The discrepancy will accumulate very slowly, and it is more convenient for science and navigation to take into account data on the Earth's rotation separately, without jumps in the main scale," the expert says.

For this reason, maintaining a difference of less than one second has ceased to be a prerequisite for most modern technical systems.

At the same time, people's biological rhythms are so inert that such changes do not harm in any way, says Elena Mikheeva. In the future, the Earth will continue to slow down, but since this is happening very slowly, it will take 20-30 years at the earliest to remove another second.

"Sometimes global cataclysms like powerful earthquakes can slightly accelerate the rotation of the planet, but we are talking only about microseconds — barely one full second will run in 100 years," the Izvestia interlocutor emphasizes.

Is it possible to "smear" an extra second

It is quite possible to "smear" a moment by actually dissolving it in time: this method is already being used and is called leap smear, says Svyatoslav Litvinov. Its principle is that instead of adding a whole second ("jump") at a certain moment, the system changes the speed of the program clock quite a bit for a while. As a result, an additional moment is allocated, for example, for the entire day, and then the clock again exactly matches UTC.

— This approach is used by large Internet companies, because for servers, a smooth correction is usually safer than an abrupt change in the timeline. This is not a single standard: different systems use their own smear algorithms, which is why the clocks temporarily diverge. Therefore, the transition to continuous UTC should in the future remove the very need to regularly solve this problem in various technical ways," the scientist summarizes.