complete aether drag, as the spinning surface of the Earth experiences an aether wind. The Michelson-Morley experiment shows on the contrary that a hypothetical aether could not be moving relative to the Earth, that is, as the Earth orbits it would have to drag the aether along. Those two results are not incompatible per se, but in the absence of a model to reconcile them, they are more ad hoc than the explanation of both experiments within special relativity. The experiment is consistent with relativity for the same reason as all other Sagnac type experiments (see Sagnac effect). That is, rotation is absolute in special relativity, because there is no inertial frame of reference in which the whole device is at rest during the complete process of rotation, thus the light paths of the two rays are different in all of those frames, consequently a positive result must occur. It's also possible to define rotating frames in special relativity (Born coordinates), yet in those frames the speed of light is not constant in extended areas any more, thus also in this view a positive result must occur. Today, Sagnac type effects due to Earth's rotation are routinely incorporated into GPS. References Physics experiments Aether theories 1925 in science