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Thread: How do we know the CMB happened at t+380,000 years

  1. #1
    Join Date
    Oct 2008
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    How do we know the CMB happened at t+380,000 years

    I keep reading that the cosmic microwave background (CMB) radiation was released at the point-in-time when photons were first able to move freely - and this was at 380,000 years after the Big Bang (which I'm calling t=0).Can someone explain in layperson terms how the 380,000 year period was determined? Thanks!

  2. #2
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    Just a quick explanation: It assumes that the model of the early universe is fairly close to correct. How long after the big bang had the universe cooled enough for atoms to dominate over plasma? 380,000 years. A lot of computer modeling and the observations of the microwave probes were used to get the number fairly precisely for those models.
    Forming opinions as we speak

  3. #3
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    Quote Originally Posted by antoniseb View Post
    ...How long after the big bang had the universe cooled enough for atoms to dominate over plasma? 380,000 years....
    Right. It is known how cool it must be for protons to capture and hold onto electrons. Then, if I'm not mistaken, it's estimated how long it took to reach that temperature based on the rate of expansion (since as the Universe expands, it cools) and based on the current 2.7K temp of the CMB.
    Everyone is entitled to his own opinion, but not his own facts.

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