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Introducing the World’s Most Precise Clock

An optical-lattice clock could lose just a second every 13.8 billion years

18 min read
Introducing the World’s Most Precise Clock
Illustration: Erik Vrielink

In 1967, time underwent a dramatic shift. That was the year the key increment of time—the second—went from being defined as a tiny fraction of a year to something much more stable and fundamental: the time it takes for radiation absorbed and emitted by a cesium atom to undergo a certain number of cycles.

This change, which was officially adopted in the International System of Units, was driven by a technological leap. From the 1910s until the mid-1950s, the most precise way of keeping time was to synchronize the best quartz clocks to Earth’s motion around the sun. This was done by using telescopes and other instruments to periodically measure the movement of stars across the sky. But in 1955, the accuracy of this method was easily bested by the first cesium atomic clock, which made its debut at the United Kingdom’s National Physical Laboratory, on the outskirts of London.

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