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Homework Help: Thomson Scattering In the Early Universe

  1. May 16, 2017 #1
    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. jcsd
  3. May 17, 2017 #2


    User Avatar
    2017 Award

    Staff: Mentor

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