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To understand why light moves away from its source as an expanding spherical wave front, we need Einstein’s theory of special relativity. Not only does light move through space and time, but Einstein taught us that the structure of space and time informs light how to move. Much like the wind propels a sailboat’s motion, light is sailing the winds of spacetime so to speak. Einstein’s resolution to his paradox about riding a light wave was that space and time had to be merged into four-dimensional spacetime. We no longer exist at a point in three-dimensional space but at a point in four-dimensional spacetime.