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

Current tests of light-speed invariance have historically measured potential anisotropies due to the unknown motion relative to hypothetical preferred frames. Null results can’t invalidate light-speed anisotropy but only establish upper limits on this unknown velocity. We propose a fundamentally different experimental approach using lab-controlled motion, enabling definitive result rather than upper limit. An innovative motion-controlled close-loop interferometric setup is designed to detect two-way light speed variation with first-order sensitivity (c±v), where v is the lab-controlled motion. Our configuration eliminates that dependency by introducing a controlled, deterministic motion 𝑣, allowing a definitive test. Unlike traditional tests limited by second-order effects (v^2⁄c^2 ), our design achieves theoretical sensitivity to controlled motions as small as 0.1 m/s—approximately 10^4-fold improvement. The key methodological innovation is that when we set v>2δ, with δ as the total experimental uncertainty, the predicted outcomes for light-speed invariance versus anisotropy theories become non-overlapping and empirically distinguishable. Hence, it provides a definite “Yes/No” answer to which theoretical prediction matches the experimental results. 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 describes an experimental approach that definitely determines which theoretical prediction aligns with observed reality, without relying on a particular theory. Regardless of the outcome, implementing this experiment will address a long-standing gap and contribute substantially to fundamental physics.