The best modern atomic clocks are so stable that they wouldn't lose or gain a single second in —a span of time longer than the age of the universe.

You likely interact with atomic clocks every day without realizing it:

Cesium atoms are sprayed into a vacuum chamber and hit with microwaves.

Since 1967, the International System of Units (SI) has defined one second as exactly 9,192,631,770 oscillations of the radiation produced by this transition in a cesium-133 atom. Why It Matters

If the microwave frequency is exactly right, the atoms change states.

GPS satellites carry atomic clocks. Because radio signals travel at the speed of light, even a billionth of a second of error could result in your GPS being off by several miles.

High-speed data transfers and cellular networks require perfectly synchronized "stamps" to ensure packets of data arrive in the correct order.