The General Conference on Weights and Measures, meeting in Versailles, may put an end to the dispute over leap seconds. Delegates from various countries are due to vote on a transition to continuous universal time, UTC, which would no longer have to be adjusted to the Earth's uneven rotation. The vote on the matter is scheduled for October 15.
The reform has been in preparation for several years. As early as 2022, metrologists agreed to increase the permissible divergence between UTC and the astronomical time UT1 no later than 2035. The draft of the current resolution proposes launching continuous UTC from May 20, 2027. The maximum difference between the two time scales is planned to be increased from the current 0.9 seconds to one hour. This gap would accumulate gradually as the planet's rotation slows or speeds up, so the next major time correction would not be needed for several centuries.
UTC is based on readings from atomic clocks, while UT1 reflects the actual rotation of the Earth. The planet's rotation speed constantly changes due to processes in its interior, atmosphere and oceans. Since 1972, this difference has been compensated by adding so-called leap seconds to UTC. Since then, 27 have accumulated.
For a person, an extra second is almost imperceptible, but it creates difficulties for computer systems. Servers, communication networks and power grids use precise time stamps to determine the order of events. An abrupt change in system time can disrupt their synchronization. For this reason, large technology companies already apply various methods of "smoothing" the leap second, but the incompatibility of these methods can itself lead to discrepancies.
The solution has been accelerated by unusual behavior of the Earth: in recent years, it has been rotating faster. As a result, for the first time, it may be necessary not to add but to subtract one second. Experts on the Earth's rotation estimate the probability of such a scenario by 2035 at roughly 30%. Digital infrastructure is not prepared for such a "negative leap second."
The authors of the resolution warn that subtracting a second would create a particularly high risk for transport, energy and satellite systems. Abolishing leap seconds will not cancel the astronomical time UT1 — it will continue to be measured for the needs of astronomers and satellite navigation. However, for most computer systems, UTC will become a continuous time scale independent of the planet's motion.
Letters