3. The First Atoms
TIMELINE · 380,000 years in
For 380,000 years the universe was a glowing fog, too hot for atoms: electrons flew free and light could not travel. Then it cooled below about 3,000 degrees, electrons settled around nuclei, the first true atoms formed, and light suddenly ran free. That first released light still fills the sky today as the cosmic microwave background, the universe's baby photo.
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