When did neutral atoms first form in the early universe?

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Examine the observable universe's place within the whole universe — Cosmology Learn about defining and measuring the observable universe within the “whole” universe.

In the context of cosmology, neutral atoms first formed in the early universe approximately 380,000 years after the big bang.1

During the initial stages of the universe, temperatures were too high for electrons to remain attached to nuclei, resulting in a hot, opaque plasma. As the universe expanded and cooled, it eventually reached a state where the temperature was sufficiently low—roughly 3,000 K—to allow electrons to bind to nuclei to form stable, neutral atoms. This process is known as recombination.2341

Once these neutral atoms formed, the radiation that had previously been trapped by the plasma was free to travel through space. This "first light" is observed today as the cosmic microwave background radiation.31