Conclusively Test Light-Speed Invariance with a Motion-controlled First-order Sensitive Interferometer

This paper proposes an innovative motion-controlled close-loop interferometric setup which can directly measure two-way light speed variation with first-order sensitivity (c±v), where v is a lab controlled motion All current tests of light speed invariance, whether interferometric or cavity-based, provide only upper limits rather than conclusive results, due to their reliance on unknown motion in hypothetical frame. Our configuration eliminates that dependency by introducing a controlled, deterministic motion 𝑣, allowing a definitive test. Traditional Michelson–Morley interferometric tests face further challenge due to the limit of second-order sensitivity, 𝑣2𝑐2⁄, constraining the upper limit to ~1 km/s. Modern cavity-based tests claim higher precision but measure frequency shifts rather than direct time-of-flight. Our configuration allows for the direct detection of light speed deviations caused by v as small as 0.1 m/s, compared to the ~1 km/s for the traditional M-M interferometer. This design closely aligns with the generalized Sagnac effect and can be extended to test the new prediction of Sagnac effect in inertial frame per Asymmetry Theory. This paper presents an experimental setup without assuming any specific theory. Regardless of the outcome, implementing this experiment will address a long-standing gap and contribute substantially to fundamental physics.