Novel Interferometer with First-Order Sensitivity for Detecting Two-Way Light Speed Deviations

Interferometric methods can measure the speed of light c with a precision of ±1.1 m/s. However, directly detecting deviations from c in two-way (round-trip) light speed measurements using a traditional interferometer remains challenging due to their second-order sensitivity. This paper introduces an innovative interferometer setup designed to detect two-way light speed deviations with first-order sensitivity (c±v), where v is a tunable deviation parameter and independent of the choice of reference frame. Our configuration can directly detect the light speed deviation of 0.1 m/s, a 10^4-fold improvement over traditional Michelson–Morley interferometer measurement. This setup significantly enhances measurement fidelity and offers a new pathway to directly and conclusively test the invariance of light speed in all inertial frames. This design aligns closely with Sagnac effect and can be modified to test a new prediction of Sagnac effect in inertial frame.