Atomic clocks are the world’s most precise timekeepers. Based on periodic transitions between two electronic states of an atom, they can track the passage of time with a precision as high as one part in a quintillion, meaning that they won’t lose or gain a second over 30 billion years—more than twice the age of the universe.

​Atomic clocks are the world’s most precise timekeepers. Based on periodic transitions between two electronic states of an atom, they can track the passage of time with a precision as high as one part in a quintillion, meaning that they won’t lose or gain a second over 30 billion years—more than twice the age of the universe. General Physics Quantum Physics