A global timekeeping body in France has decided to eliminate “leap seconds” after more than 50 years of use. This move means that clocks will gradually drift out of sync with the Earth’s rotation by up to a full hour, a process that could take centuries or even millennia.

The precise atomic time, established in the 1950s by tracking atomic vibrations, is slightly out of sync with solar time based on the sun’s position due to the Earth’s gradual rotation slowdown. The leap second, introduced in 1972 with an immediate addition of ten seconds, aimed to correct this discrepancy.

The International Earth Rotation and Reference Systems Service has since monitored the difference between solar and atomic time to determine when to insert an extra second. Leap seconds have been added 27 times, most recently in 2016. Without these adjustments, significant changes like having the brightest part of the day at midnight could occur over time.

Similar to leap years adding days to keep calendars aligned, leap seconds maintain time accuracy. However, leap seconds are increasingly challenging for modern systems reliant on precise timekeeping. Companies implement leap seconds differently, posing risks of system failures and disruptions.

Recent discussions suggest a potential need for a “negative leap second” as Earth’s rotation has accelerated. The decision to accumulate extra seconds up to an hour before making adjustments was passed by the International Bureau of Weights and Measures, effective from May 2027.

While some experts express concerns about the implications for technology-driven economies, others emphasize the inevitability of imperfections in timekeeping systems due to various factors influencing Earth’s rotation speed. Accepting slight inaccuracies in time tracking seems to be an enduring challenge in our timekeeping history.