What is the name given to the observed background radiation that supports the Big Bang theory?

The observed background radiation that supports the Big Bang theory is called Cosmic Microwave Background Radiation (CMBR). This radiation is a remnant from the early universe, specifically from about 380,000 years after the Big Bang when the universe cooled sufficiently for protons and electrons to combine and form neutral hydrogen atoms, allowing photons to travel freely. The CMBR is detected as a nearly uniform glow across the entire sky, with a characteristic temperature of about 2.7 K, and its presence provides vital evidence for the hot, dense state of the universe in its early moments.

This background radiation is consistent with predictions made by the Big Bang theory and has been studied extensively through various satellite missions, such as the COBE, WMAP, and Planck missions. The uniformity and spectrum of the CMBR support the idea that the universe expanded from an initial high-energy state, reinforcing the Big Bang model.

In contrast, while gamma radiation, infrared radiation, and ultraviolet radiation are all forms of electromagnetic radiation, they do not specifically relate to the early universe. They are associated with different physical processes and sources, such as high-energy events, thermal emissions from objects, and various astrophysical phenomena.