But we can do better. A new generation of atomic clocks that use laser light instead of microwave radiation can divide time more finely. About six years ago, researchers completed single-ion versions of these optical clocks, made with an ion of either aluminum or mercury. These surpassed the accuracy of cesium clocks by a full order of magnitude.
Now, a new offshoot of this technology, the optical-lattice clock (OLC), has taken the lead. Unlike single-ion clocks, which yield one measurement of frequency at a time, OLCs can simultaneously measure thousands of atoms held in place by a powerful standing laser beam, driving down statistical uncertainty. In the past year, these clocks have managed to surpass the best single-ion optical clocks in both accuracy and stability. With further development, they will lose no more than a second over 13.8 billion years—the present-day age of the universe.