As the universe continued to expand, the temperature of the cosmic soup finally dropped below 2,967 Kelvin. Electrons began to combine with protons to form neutral hydrogen.

• 当宇宙不断膨胀,宇宙的温度亦随之下降,当温度低于2,967绝度温度时,电子和质子便会开始结合而成为中性的氢原子。