# Thomson Scattering In the Early Universe

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1. May 16, 2017

### bananabandana

1. The problem statement, all variables and given/known data
Why does Thomson scattering occur in the early universe?

2. Relevant equations

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

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 :)

2. May 17, 2017

### Staff: Mentor

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