Hi Daniel, The Sun's energy is transported as light from the core to the surface. In order to do so, it must pass through a very very dense region called the radiative zone. This region is so dense that a light particle can only travel a very short distance before it gets absorbed. Once a particle of light is absorbed, it can be reemitted and move along a short distance again and get absorbed and so on and so on. This is what is known as a "random walk" because we can't predict which way the light will go, we just know it probably won't be in a straight line! Because the light has to go on this tangled up path to get to the surface, it takes on packet of light more than 100,000 years to get from the core to the surface! Claire