Abstract

The Michelson-Morley experiment for examining light-speed constancy in paths moving linearly is second-order in speed, so it has never been conducted with paths moving relative to Earth. The Sagnac experiment is a first-order experiment, but it does not address motion that is linear, since its path motion is caused by rotation. The design of an interferometric experiment that is not only sensitive to linear motion, but also first-order in speed, needs two features: 1) optical paths in uniform translational motion, and 2) paths for light return without cancellation of possible effects. Two arrangements with these features are here presented: a conveyor-like arrangement, and a shearing parallelogram arrangement. Both can be implemented with fiber-optic technology. If the entire optical loop is fiber, the light-speed constancy in a moving path of the fiber is examined; if the fiber loop is broken to leave a gap of vacuum (or air), the light-speed constancy in a moving path of vacuum (or air) is examined. According to the same analysis as that for a fiber-optic gyro, translational motion in these arrangements will lead to an increase of optical path length and an increase of the travel time difference, a result falsifying the principle of the light-speed constancy.