A First-order Sensitive Interferometer Measuring Two-Way Light Speed Variance for Linear Motion

Currently, all tests of light speed invariance provide only upper limits not conclusive result, due to their reliance on hypothetical preferred frames. Traditional Michelson–Morley interferometric tests face further challenge due to the limit of second-order sensitivity, v²/ c², constraining precision to ~1 km/s. Modern cavity-based tests measure frequency shifts rather than direct time-of-flight, leaving questions about validity.

A motion-controlled interferometric setup adopting innovative closed-path design is designed to measure two-way light speed deviations with first-order sensitivity (c±v), where v is a tunable value set by the tester and independent of the choice of reference frame. Our configuration can directly detect two-way light speed deviations with v ~ 0.1 m/s — a 10^4-fold improvement over traditional M–M interferometer. Importantly, a linear relationship between the variance and v is expected, eliminating the dependency on a hypothetical frame. Hence, the outcome yields definitive conclusion rather than an upper limit. This configuration aligns with the Sagnac effect and enables testing a novel prediction of Sagnac effect in inertial frame per Asymmetry Theory.

A null result would conclusively confirm light speed invariance, whereas any observed deviation could support alternative theories, such as Asymmetry Theory. Regardless of the outcome, implementing this proposal is expected to address a longstanding gap and make a significant contribution to fundamental physics.