it might be best to first detail my (admittedly limited) understanding of the LIGO experiment. a beam of light is split along two 4Km evacuated pipes then reflected back where their interference pattern is analysed for any disturbances in the interference pattern, any contraction or extension in the time the split beams took to travel will be detected in the interference pattern of the two beams when they return. when a gravitational wave passes it leads to a change in the length of one of the arms relative to the other by stretching or contracting the space that arm is in as a result one beam will return at a very slightly different time to the other. assuming that my understanding of the experiment is not flawed does this mean that to an outside observer the light along the contracted arm made the trip in less time than would have been made in normal circumstances by light and furthermore is this in any way similar to how the fictional alcubierre drive would function?
i'm not asking if the beams themselves travelled faster than light (i know everyone's tired of questions like that from rookie physics students like myself) just if to an outside observer it would appear that they made the trip in a time that would be less than normal i.e. if an outside observer not affected by the gravitational waves would theoretically see an arm of the experiment contract