Overview
- The Generalkonferenz für Maß und Gewicht decided in Versailles during its Oct. 13–15 meeting to stop routine leap seconds and permit UTC to differ from UT1 by as much as 3,600 seconds, with the new continuous UTC taking effect on 20 May 2027.
- Delegates moved because recent, faster-than-expected swings in Earth’s rotation raise the chance of a never-before-used negative leap second and because sudden one-second adjustments have disrupted computer systems, networks and some critical infrastructure.
- Everyday clocks and civil time will look the same for most people for the foreseeable future, but astronomy, geodesy and high-precision systems will need to track UT1 separately and adapt workflows to a steadily drifting relation between clock time and the position of the sun.
- Work on a formal redefinition of the SI second using far more precise optical atomic clocks will continue and is not being adopted now, with a concrete proposal targeted for the 2030 General Conference once international comparison and signal-transfer methods meet strict requirements.
- Optical clocks offer roughly 100 times lower uncertainty than cesium standards and require careful international comparisons and relativistic corrections for height and gravity, so labs and time services will need years of coordination and new transfer methods before a redefinition can proceed.