Where did the cosmic microwave background (CMB) come from?

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The cosmic microwave background (CMB) is a faint glow of light that pervades the entire universe. It is made up of photons that were released when electrons and nuclei combined for the first time, about 380,000 years after the Big Bang. This event is known as recombination and is responsible for making the universe transparent to light. The photons from the CMB have been traveling through space ever since, gradually cooling as the universe has expanded. The CMB is now at a temperature of about 2.7 K, making it one of the coldest things in the universe. The cosmic microwave background (CMB) is radiation that originated from the hot, dense plasma of the early universe when electrons and nuclei combined to form neutral atoms. This occurred about 379,000 years after the Big Bang and the radiation has been traveling through the universe ever since, providing a snapshot of the conditions in the early universe.

Where Did the Cosmic Microwave Background (CMB) Come From