Even though the frequency survives the long trip, any changes in that frequency are observed only after a delay corresponding to the speed of light. Someone on

Even though the frequency survives the long trip, any changes in that frequency are observed only after a delay corresponding to the speed of light. Someone once pointed out that shadows (which aren't objects with a mass and position) can move fast than light, at a sufficiently large distance from their origin. That is, the location of the border between the shadowed and unshadowed region can be changing faster than light speed. But that fact can't be used to communicate faster than light, because the changes in the location of the shadow's edge still take a comparatively enormous amount of time to propagate from their source to their destination. If you're creating the shadow, you can know that one galaxy will observe the shadow long before another galaxy does, but you can't use that knowledge to signal something to one galaxy or the other without waiting for the light (or lack of light) to travel all the way to that galaxy.