A new experiment using precise laboratory motion can finally prove once and for all if the speed of light is the same in every direction.
April 25, 2026
Original Paper
A Definitive Test of Light-Speed Invariance Using First-Order Interferometry with Controlled Motion
SSRN · 6642040
The Takeaway
Physicists have spent over a century trying to detect if light moves faster or slower depending on how you are moving through space. Previous tests like the famous Michelson-Morley experiment could only set upper limits on how much the speed varied. This new setup is 10,000 times more sensitive and uses controlled motion to provide a definitive yes or no answer. It moves the conversation from setting limits to establishing a hard fact. This test will serve as the ultimate trial for the core foundation of modern relativity.
From the abstract
Current tests of light-speed invariance have historically measured potential anisotropies due to the unknown motion relative to hypothetical preferred frames. Due to overlapping/indistinguishable predictions, null results can’t rule out light-speed anisotropy but only establish upper limits on this unknown velocity. We propose a fundamentally different experimental approach eliminating that dependency on hypothetical frames with the introduction of a lab-controlled, deterministic motion 𝑣, and e