E. Peik

A laser beam as faint as a whisper of light has stirred a thorium-229 nucleus into a higher energy state. Most nuclei demand a blast of energy, but thorium-229 has such a tiny energy gap that even this gentle nudge works.

The most precise modern clocks count time by the oscillations of electrons in atoms. But their rhythm can be thrown off, like a mechanical watch's spring gets jolted by shaking. Physicists found a more reliable pendulum: the atomic nucleus.