For decades, scientists have relied on atomic clocks to keep the world’s most accurate time. These clocks are so reliable that they power technologies such as GPS navigation, telecommunications networks, and high-frequency financial trading. Now, a new generation of clocks is pushing precision even further—so far, in fact, that researchers believe it could eventually redefine the very meaning of a second.
From Cesium to Optical Timekeeping
The current international definition of a second is based on the vibration of cesium atoms. Since 1967, the second has been defined using the microwave frequency emitted by cesium-133 atoms in specialized atomic clocks. These clocks are incredibly accurate, drifting by only about one second over tens of millions of years.
However, scientists have discovered that optical clocks can perform far better. Instead of microwaves, these clocks use lasers to measure extremely fast oscillations in atoms such as strontium or ytterbium. Because light oscillates much faster than microwave radiation, optical clocks can divide time into much smaller intervals and measure it with far greater precision.
A Clock That Barely Loses Time
Recent optical lattice clocks have demonstrated astonishing stability. Some versions would lose or gain just one second over billions of years. In laboratory tests, these clocks measure atomic vibrations with such precision that their accuracy reaches the 18th decimal place.
To achieve this performance, researchers cool atoms to extremely low temperatures and trap them in a grid of laser light known as an optical lattice. This arrangement allows scientists to measure the atoms’ natural oscillations with extraordinary consistency.
Redefining the Second
Because optical clocks are more than 100 times more precise than today’s cesium clocks, scientists are now exploring whether they should replace the current standard for defining the second. International metrology organizations are already studying the possibility, and many researchers expect a new definition to emerge within the next decade.
If adopted, this new standard would not change the length of a second in everyday life. Instead, it would make our measurement of time far more exact—unlocking improvements in navigation, fundamental physics experiments, and even the search for dark matter.
