Scientists have built the first operating nuclear clock, and it could change timekeeping forever.

Today’s atomic clocks count the vibrations of electrons, losing less than a second over millions of years. Nuclear clocks go deeper, tracking transitions inside the atomic nucleus, which is shielded from outside disturbances.

The key is thorium-229, an isotope with a rare low-energy nuclear transition that lasers can reach. A working nuclear clock could be ten to a hundred times more precise than the best atomic clocks.

That matters for GPS, which depends on exact timing, and for testing whether the fundamental constants of nature are truly constant. It could even help hunt for dark matter.

After decades of failed attempts, researchers have finally isolated the signal and kept a nuclear clock running. The race is now on to make the technology practical.

For now, nuclear clocks remain laboratory instruments, but history suggests today’s experiments become tomorrow’s infrastructure. The atomic clock itself was once a lab curiosity before it started running the modern world.