Representatives from 69 countries voted on 15 October to abandon leap seconds at a meeting of the International Bureau of Weights and Measures (BIPM) in Versailles, France [1]. The decision moves global timekeeping away from periodic adjustments that kept Coordinated Universal Time (UTC) aligned within one second of astronomical time, known as UT1 [2]. Official clocks will now run continuously without abrupt pauses [1]. Metrologists agreed that the new standard will take effect on May 20, 2027, coinciding with World Metrology Day to protect telecommunications networks and navigation systems [2].
Versailles Vote Ends the Leap Second
Diplomats and metrologists gathered at the General Conference on Weights and Measures (CGPM) in Versailles to resolve disputes over international timekeeping. The resolution won by a majority vote. It puts an end to a system that has governed official clocks since 1972 [1, 2]. Voting delegates agreed that tolerating a wider divergence between atomic clocks and Earth’s spin provides the safest path forward for digital networks [2].
Noël Dimarcq addressed delegates just before the final ballot took place at the General Conference on Weights and Measures in Versailles, France. Dimarcq works as a senior scientist at the French National Center for Scientific Research (CNRS) and serves as president of the BIPM Consultative Committee for Time and Frequency. “After 30 years of debates, we are ready,” said Dimarcq. The representatives from 69 countries approved the measure without delay [1, 2].
Under the rules adopted in 1972, physicists added 27 leap seconds to Coordinated Universal Time whenever planetary rotation drifted out of sync with atomic clocks. That strategy is now being abandoned in favor of a much larger tolerance window [1]. Official UTC will be allowed to diverge from astronomical UT1 by up to an hour, or 3,600 seconds, before any correction is required [2]. Emily Akkermans, curator of time at the Royal Observatory in Greenwich, London, said that this slow widening will eventually be “like living on daylight saving time” on a permanent basis. But the shift accumulates so slowly that ordinary people will not perceive any change in their daily routines [1, 2]. Setnam Shemar at the National Physical Laboratory (NPL) in Teddington, UK, said that “it’ll be many hundreds or even thousands of years before a leap hour is needed” [1].
Why Clocks Broke Away from the Sun
For most of recorded history, human beings set their clocks by the apparent position of the sun in the sky. Local solar noon guided daily life and seasonal work in every farming community. But as industrial rail transport and telegraph wires connected distant towns, communities needed standardized civil hours that did not shift with every local meridian. Solar time could no longer support global connectivity [1, 2].
Earth is not an ideal clock for modern civilization. When international agencies created Coordinated Universal Time in 1960, researchers soon discovered that our planet was slowing down because tidal friction, shifting ocean currents, and deep mantle convection alter planetary rotation speed from year to year [1, 2]. In 1967, physicists at the International Bureau of Weights and Measures in Versailles redefined the base second by anchoring the unit to microwave vibrations inside the caesium-133 atom. At the behest of astronomers, the BIPM introduced leap seconds in 1972 to keep atomic counts aligned with solar time [1, 2]. Adjustments occurred in either June or December. But because rotational changes remain irregular, metrologists could never predict these adjustments more than six months in advance [1, 2].
Digital Networks and the Negative Second Threat
Single-second pauses caused few complications during the 1970s. Today, however, automated computer systems govern telecommunications networks, global financial exchanges, air traffic routing, and electrical power grids that demand uninterrupted synchronization to order database entries and verify transactions across international borders without a microsecond of unexpected delay. Sudden pauses create dangerous software errors. These freezes can bring down major digital services in mobile networks and power grids without warning [1, 2].
Setnam Shemar from the National Physical Laboratory (NPL) in Teddington, UK, pointed out that past leap seconds caused major websites to crash and severely disrupted airline reservation systems. Emily Akkermans at the Royal Observatory in Greenwich also warned of the growing danger for automated systems. “Time is now so much more important and integrated into these systems,” said Akkermans. “What once worked has become more problematic”. Software engineers found that even scheduled pauses produced software glitches [1, 2].
The situation grew urgent in the mid-2010s when Earth’s rotation began speeding up rather than slowing down. Scientists realized that instead of adding a second, they might soon need to subtract one by introducing a negative leap second as early as 2029. Skipping a second has never been tested in public computer networks [1, 2]. Engineers warned that subtracting a second would act like a “mini Y2K” event because database software cannot easily process time running backwards. Nick Stamatakos, head of the Earth Orientation Department at the U.S. Naval Observatory, confirmed the concern. “Avoiding negative leap seconds is a very big driver to open the window,” said Stamatakos, whose department manages timing for the American GPS satellite network [2].
How a Leap Hour Replaces Regular Adjustments
To eliminate these software hazards, BIPM delegates in Versailles voted to abandon leap seconds and allow atomic time to run continuously. Under the new policy, the difference between astronomical UT1 and UTC will expand up to a full hour before any corrective action occurs [1, 2]. Society already adjusts clocks by an hour for seasonal daylight saving time without crashing power grids or flight software. A leap hour provides an orderly solution [1, 2].
The resolution will take effect on May 20, 2027, giving telecommunications providers and operating system vendors several years to update their synchronization protocols [1, 2]. Noël Dimarcq said that letting the time gap grow will protect automated networks and provide uninterrupted time for “several centuries”. Metrologists at the BIPM estimate that a leap hour will not be needed for at least 1,000 years [1, 2]. This extended window effectively ends the BIPM procedure of tying civil time directly to the sun’s position in the sky [2]. Just as environmental monitoring shows how planetary boundaries breached across Earth systems demand coordinated global observation, geophysicists will continue tracking how melting glaciers and core dynamics shift Earth’s spin [1]. But civil clocks will no longer pause for tiny rotational wobbles [2].
Atomic Standards and Future Lunar Time
The Versailles conference looked well beyond the present leap second problem. Metrologists addressed deeper challenges in quantum measurement and interplanetary exploration. Because atomic instruments have advanced considerably since 1967, delegates invited national metrology institutes to prepare detailed proposals for a newly revised definition of the SI second. The goal is to anchor time to even more stable natural phenomena [1].
The current standard relies on microwave frequencies emitted by caesium-133 atoms, but newer laboratory devices operate at optical frequencies. These optical clocks use laser beams to measure atomic vibrations that oscillate hundreds of thousands of times faster than microwaves. They achieve measurement precision far beyond the reach of older caesium technology. Researchers at institutes like the National Physical Laboratory in Teddington and CNRS in France expect the updated definition to take effect once laboratories establish reliable international cross-comparisons [1].
The BIPM also asked international space agencies to establish a unified time standard for the moon. As national agencies prepare permanent lunar habitats, synchronizing equipment between Earth and lunar orbit has become a pressing practical necessity. Just as physiological changes documented in astronaut ageing research on orbital missions show the biological challenges of spaceflight, relativistic mechanics alters the flow of time itself in lower gravity environments. Lunar clocks run faster than clocks on Earth because gravity is weaker on the lunar surface. Noël Dimarcq said that these collective reforms “will have a profound impact on future timekeeping both on Earth and other planets”. Standardized lunar time will support safe robotic landings and reliable satellite navigation across future interplanetary corridors [1].
Tracking Planetary Spin Without Leap Seconds
Scientists will not stop tracking planetary rotation. Astronomers and space navigators at the U.S. Naval Observatory and Greenwich still require precise observations of Earth’s orientation relative to the stars, using radio telescopes and laser tracking to measure daily variations in axial velocity. The Versailles resolution simply untangles observational astronomy from civilian computer networks [1, 2].
Setnam Shemar at the National Physical Laboratory in Teddington said that physicists will continue to track Earth’s spin with high precision to supply observational data for celestial navigation and deep space tracking. The U.S. Naval Observatory and the BIPM will keep publishing regular UT1 data for scientific users who need astronomical coordinates. For everyday society, the reform brings stability to an increasingly digital economy. When the Versailles agreement takes effect on World Metrology Day in 2027, human civilization will officially end half a century of awkward one-second interruptions. Computers and communication satellites in the GPS network will finally operate on continuous atomic time without looking back to the sky [1, 2].
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APA 7: PerEXP Teamworks. (2026). BIPM Delegates Vote to Abolish Leap Seconds by 2027. PerEXP Teamworks.
