The Best Atomic Clock Won't Lose a Second in 30 Billion Years

In 2024, physicists at JILA — a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder — unveiled the most accurate atomic clock ever built. Its timekeeping is so stable that, in this class of optical clock, the error amounts to losing only one second every 30 billion years.

To put that in perspective, the universe is about 13.8 billion years old. The clock would have to run for more than twice that span before it slipped a single second.

The secret is strontium atoms held in a lattice of laser light. Instead of microwaves, like the cesium clocks that define today’s official second, the atoms “tick” at optical frequencies — hundreds of trillions of times per second — letting the clock slice time far more finely.

The reported systematic uncertainty reached 8.1 × 10⁻¹⁹, the lowest ever measured.

Such precision is more than a record. Clocks this exact can test Einstein’s relativity, hunt for dark matter, and sense gravity so keenly they could one day help map the planet or guide navigation to Mars.