radiative diffusion: Energy produced in the center of the Sun flows toward the outer layers. In the radiative zone, the energy moves by the process of diffusion and is called radiative diffusion. Diffusion is the natural mixing of atoms and molecules. Diffusion can occur with gases and liquids. In a gas or a liquid the molecules are free to spread out, or diffuse, throughout another gas or liquid. For example, over time, a drop of food coloring will mix with water in bowl. Diffusion is a very slow process. It is estimated that it takes energy millions of years to move from the center of the Sun to the photosphere.
