"Using light to see the world requires speed of light to be maximum?" As in some posts, one may argue that massive body can move faster than light has nothing at all to do with whether or not we "observe" the universe through light. Or a blind person would have a maximum speed of sound.. But the blind person can simply do experiment himself or know from other people that something travelling at higher speed than sound And in many illustration in explaining relativity, for example the train with a person in the centre, and the calibration of A ,B ,C clocks, etc.. they require the use of light rays. But one may argue that after we do experiment through light, we can be confident to describe physical law the same way as we dont use light. However it sounds not very natural . Is it a common sense that if we use light to calibrate something, we must set light to have the maximum speed?