An objective world has only one type of movement, that of the object, but virtual worlds always have two. In Figure 5.6, one can move the avatars to the left by moving their pixels left or by moving the forest pixels behind them right. A program can create movement by moving the object or its background as the avatars move relative to the forest. Programs can move images by bit-shifting the foreground or the background. In the first case, avatar pixels move across the screen and in the second case, the background pixels scroll behind the center-screen object’s frame of reference.
Our reality also has two movement types, of light that is absolute and of matter that is relative to its frame of reference. Light and matter move differently in our reality just as in a virtual reality. Light moves like a pixel crossing a screen while matter moves like a center-screen image whose background scrolls. The standard model assumes particles move on a stationary background but relativity describes the option to bit-shift the background. In a fast car, one can imagine being still with the world scrolling by, perhaps because it is actually so.