> Importantly, gravitational waves are not waves of Newtonian gravity. Gravitational waves do not "push and pull" along the direction of propagation. They stretch and compress space along axes perpendicular to the direction of propagation.
This may be, likely is, a stupid question, but how do you measure this if space itself is stretched or compressed? Won't any yardstick lying in that space also be stretched or compressed? Or is it a matter of this distortion of space changing geodesics through it so light following a straight line will end up in a different place? It seems that LIGO uses interferometry to measure a change in distance between two points, though, and I don't understand how that can be measured if space is stretched, only if space is added. Perhaps that is the answer right there: when space is stretched dimensionless particles traveling through that space are not stretched, because they are dimensionless. Or perhaps better, objects in space stretch, but their momentum vectors don't stretch.
This may be, likely is, a stupid question, but how do you measure this if space itself is stretched or compressed? Won't any yardstick lying in that space also be stretched or compressed? Or is it a matter of this distortion of space changing geodesics through it so light following a straight line will end up in a different place? It seems that LIGO uses interferometry to measure a change in distance between two points, though, and I don't understand how that can be measured if space is stretched, only if space is added. Perhaps that is the answer right there: when space is stretched dimensionless particles traveling through that space are not stretched, because they are dimensionless. Or perhaps better, objects in space stretch, but their momentum vectors don't stretch.