Atomic clock performance beyond the geodetic limit

Understand

The passage of time is tracked by counting oscillations of a frequency reference, such as Earth's revolutions or swings of a pendulum.

• By referencing atomic transitions, frequency (and thus time) can be measured more precisely than any other physical quantity, with the current generation of optical atomic clocks reporting fractional performance below the $10^{-17}$ level.
• However, the theory of relativity prescribes that the passage of time is not absolute, but impacted by an observer's reference frame.
• Consequently, clock measurements exhibit sensitivity to relative velocity, acceleration and gravity potential.