Today’s best clocks are atomic clocks, which keep time by measuring how electrons jump between energy levels. A nuclear clock instead uses a jump inside an atom’s nucleus. Scientists at TU Wien in Vienna and Germany’s PTB, led by Thorsten Schumm and Ekkehard Peik, have now built a prototype that stabilizes itself. They shine a laser on a calcium fluoride crystal containing thorium-229 nuclei, measure how much light the nuclei absorb on either side of their resonance, and use that to automatically correct the laser’s frequency. The clock ran for more than 24 hours without anyone adjusting it. The work was reported in Nature.
It is still an early prototype. It has not beaten the best atomic clocks yet, and results still need to be reproduced between runs and labs.
Why it matters: Nuclei are less disturbed by outside forces than electrons, so nuclear clocks could one day keep even better time and be used to test big ideas in fundamental physics. To see why clocks and time are such a big deal in physics, check out our special relativity lesson.