An era in the early universe which occurred between 300,000 and 500,000 years after the big bang . During the decoupling, the temperature had fallen sufficiently for the electrons to be captured by atomic nuclei . Before decoupling, the electrons existed as a random distribution of particles throughout space.
Photons of
electromagnetic radiation frequently collided and scattered off in new directions. After the decoupling, the electrons were held close to the atomic nuclei by the force of electromagnetism. This left large volumes of space empty through which the photons could travel unhindered. In effect, before decoupling, space was opaque to radiation but afterwards, it became transparent to it. This event is observable to us today as the cosmic background radiation . The microwave emission we see today was released during the decoupling. This event brought about the cessation of radiation's dominance over matter since it removed the radiation pressure and allowed gravity to begin to shape the universe on the largest scales.
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