Optical Clocks and Relativity

TLDR

Relativity predicts that clocks in relative motion or at different gravitational potentials run at different rates, a phenomenon previously confirmed with high‑velocity atomic clocks and large altitude differences. The study aims to extend this optical clock technique to geodesy, enabling applications in geophysics, hydrology, and space‑based tests of fundamental physics. The authors compared two optical atomic clocks linked by 75‑meter fiber, measuring time dilation from relative speeds below 10 m/s and height differences under 1 m. They detected time dilation from relative speeds below 10 m/s and from height differences under 1 m, demonstrating the sensitivity of optical clocks over short distances.

Abstract

Observers in relative motion or at different gravitational potentials measure disparate clock rates. These predictions of relativity have previously been observed with atomic clocks at high velocities and with large changes in elevation. We observed time dilation from relative speeds of less than 10 meters per second by comparing two optical atomic clocks connected by a 75-meter length of optical fiber. We can now also detect time dilation due to a change in height near Earth's surface of less than 1 meter. This technique may be extended to the field of geodesy, with applications in geophysics and hydrology as well as in space-based tests of fundamental physics.