The cosmic background radiation comes from a time after the origin of the universe

Question

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The cosmic background radiation is electromagnetic radiation that is thought to have been created after the universe was approximately 380,000 years old. At this time, the universe had cooled enough for electrons to combine with nuclei to form neutral atoms, allowing the radiation to travel unimpeded through space. This radiation, which was originally in the form of high-energy gamma rays, has since cooled and stretched out to become microwave radiation with a temperature of approximately 2.7 Kelvin. Therefore, option E, when electrons began to recombine with nuclei to form atoms, is the best answer. The cosmic background radiation is often referred to as the afterglow of the Big Bang. It is the residual heat left over from when the universe was just 380,000 years old and had cooled down enough for electrons to combine with nuclei to form the first atoms. This event is known as recombination, and it is what created the cosmic microwave background radiation that we observe today.

The Cosmic Background Radiation Comes from a Time After the Origin