Radiative transfer and random walks


What happens in between? How does the energy get out, and why is it changed from gamma rays to visible light?


Radiative Transfer

Radiation and matter interact with one another: This has the effect of reducing the average energy of the radiation, and randomizing the direction of motion.

With all this going on, how can the energy get out?

via a random walk

Let's say a particle moves, on average, a certain distance between interactions:

And that it takes a total number of steps (in a random direction):
Then, on average it will have moved a distance from its starting point:
or, to move a distance d it will need a number of steps:


In the inner portion of the Sun, this is how the energy moves outwards: it random walks its way out via radiative transfer.

Question #1Why does it move outwards? Why not inwards?
Question #2: Gee this is inefficient. How long does it take the energy to get out?