At decoupling, the protons and electrons formed transparent hydrogen atoms, allowing the radiation to escape and become the present microwave background.

Question

Quizplus · Accepted Answer

At decoupling, the universe cooled enough for protons and electrons to combine and form neutral hydrogen atoms. This reduced the scattering of photons, making the universe transparent and allowing the cosmic microwave background radiation to travel freely.

At Decoupling, the Protons and Electrons Formed Transparent Hydrogen Atoms