Relativistic Sagnac Arrival Times
Compare two pulse returns using lab time and a rotating detector’s proper clock.
Free theory articleCompare two pulse returns using lab time and a rotating detector’s proper clock.
Concept & interpretation
The Sagnac effect in special relativity describes the phase shift or arrival-time difference between two counter-propagating light beams traveling around a closed loop, observed when the interferometer (or the reference frame containing the light path) is rotating. We can examine this phenomenon using an ideal circular light path of radius R in a stationary laboratory frame, and a detector moving tangentially along this path.
Experiment
You can interactively explore the Sagnac arrival times with the Relativistic Sagnac Arrival Times interactive module.
- Change the Lab radius meters to see how the total path length affects the transit times of the light pulses.
- Adjust the Speed fraction beta. Notice that for positive β, the positive direction lab time is larger, meaning that pulse arrives later. For negative β, the order of arrivals is reversed.
- Observe that when β = 0, the detector is stationary in the lab frame. The pulses arrive simultaneously, resulting in a zero arrival time difference.