Thomson Scattering In the Early Universe

[bananabandana]

Homework Statement

Why does Thomson scattering occur in the early universe?

Homework Equations

$$ e^{-} + \gamma \rightarrow e^{-} + \gamma $$
is a Thomson scattering process if:
$$ E_{\gamma} << m_{e}c^{2}$$
(Electrons are essenitally stationary)

The Attempt at a Solution

[/B]
Very confused - how is it possible that the condition is fulfilled? Surely in the early universe, we expect very high temperature, and therefore $\langle E_{\gamma} \rangle$ is very large. And the assumption that the electrons are practically stationary also seems ridiculous!

Many Thanks :)

 

[mfb]

What exactly do you call "early universe", and how large were the temperatures back then?