Today and next
What is the future of timekeeping?
The next decade brings optical clocks accurate to about a second over the age of the universe, a planned redefinition of the second (possibly around 2030), the end of leap seconds by 2035, early nuclear clocks based on thorium-229, and a separate time standard for the Moon.
Key facts
| Best optical clocks | Uncertainty around 10⁻¹⁸ |
|---|---|
| Thorium-229 nuclear transition laser-excited | 2024 |
| Leap seconds to stop | By 2035 (CGPM resolution, 2022) |
| Redefinition of the second | Roadmap targets about 2030 |
| Lunar time standard | US policy directive, April 2024 |
| Optical frequency vs cesium | About 50,000 times higher |
Timekeeping has improved by a factor of about ten every decade since the first atomic clocks. The next steps are already in laboratories.
Optical lattice clocks
Optical clocks hold thousands of strontium or ytterbium atoms in a "lattice" of laser light and measure a transition that ticks hundreds of trillions of times a second. They are so precise that they can detect the slowing of time from lifting the clock by a centimetre, which makes them sensitive gravity meters as well as clocks. Networks of optical clocks could map Earth's gravity field, monitor volcanoes and test whether the constants of nature are truly constant.
Redefining the second
Because optical clocks beat cesium by about a factor of 100, the international metrology community is preparing to redefine the second using an optical transition. The roadmap from the International Committee for Weights and Measures aims for a decision around 2030, once enough optical clocks around the world can be compared reliably.
The end of leap seconds
Leap seconds keep UTC close to Earth's rotation but cause software bugs and outages, because a minute with 61 seconds breaks a lot of code. In 2022 the General Conference on Weights and Measures voted to let the difference between UTC and Earth rotation grow beyond 0.9 seconds by 2035, effectively ending leap seconds for at least a century. See leap seconds.
Nuclear clocks
Atomic clocks use electrons. A nuclear clock would use the nucleus itself, which is far better shielded from outside disturbances. Thorium-229 has an unusually low-energy nuclear transition that lasers can reach, and in 2024 researchers in Austria and Germany excited it with a laser for the first time, and a team at JILA in Colorado then measured its frequency precisely. A working thorium clock could eventually outperform optical clocks.
Time on the Moon
Clocks on the Moon run faster than on Earth by about 56 microseconds a day, because of the weaker gravity. With crewed missions returning, a US policy directive in April 2024 asked NASA to develop a Coordinated Lunar Time, and international space agencies are working on a shared standard so lunar navigation systems can work together.
Where it all began
It is a long line from 29 notches on a bone to clocks that can feel a millimetre of gravity. The question underneath, what time actually is, is as open as it was when the first person looked up at the moon and started counting.
Questions people ask
What is the most accurate clock in the world?
Optical lattice clocks using strontium or ytterbium, with uncertainties around one part in 10¹⁸. That's about one second over the age of the universe.
Are leap seconds being abolished?
Yes, in practice. In 2022 the CGPM decided that by 2035 UTC will be allowed to drift further from Earth's rotation, so no more leap seconds will be added for a long time.
Does the Moon have its own time zone?
Not yet. NASA and other agencies are developing a lunar time standard because clocks there run about 56 microseconds a day faster than on Earth.
Sources
Last updated October 18, 2026. Found an error? Tell us.