Introduce how motion is relative and requires a reference frame. Discuss how an object may have different velocities relative to different frames of reference. Define and discuss how and why the speed of light does not change. Introduce Einstein's theory of relativity, and discuss his postulate that both space and time only exist within the universe. When you stand still, you travel through time, it you move, you travel a little through space but still mostly through time. If you travel at the speed or light, all travel is through space.