I have heard it said that an object not feeling acceleration cannot determine if he is in motion unless he sees another object to compare himself too. But what if you had an apparatus that was made of two spheres. One inside the other. Perfectly centered on each other. The inner sphere emits light pulses at a given frequency. The outer sphere is lined with photo receptors and are ALL equi-distant from the surface of the inner sphere. All Photo receptors have a clocked that is syncronized with only the photo receptors immediatly next to it (minimal distance between them). We know that the propogation of light is emitted from its 3d point in space and is subject to the doppler shift. With that said if this entire apparatus were "absolutely still" thus having "zero motion" a pulse of light from the center would reach ALL surfaces of the outer sphere at the same time and all clocks would register as recieving the light at the same time. However, if that apparatus were in motion in a given direction that same emition of light would hit the receptor that is in the opposite direction of travel earlier than the others ending with the last receptor recieving the light being the direction of travel. Since all clocks are synced to each other there is a time difference between the first and last and thus can determine the speed at which it is going. Now that you have speed and direction you have Velocity. If this is the case then can we say that something is at "absolute rest"?