Final answer:
Evidence for the Big Bang includes the cosmic microwave background radiation (CMB), which is the cooled remnant from the early universe, and the cosmological red shifts of galaxies, indicating the universe's ongoing expansion.
Step-by-step explanation:
Fill in the blank: evidence for the Big Bang includes the cosmic microwave background radiation (CMB).
The Big Bang theory is a cosmological model explaining the existence of the observable universe from the earliest known periods through its subsequent large-scale evolution. The universe expanded from a very high-density and high-temperature state, and continues to expand today. A key piece of evidence for this model includes the perfect blackbody spectrum observed in the CMB, which is characteristic of a temperature of 2.725 K. This radiation is what remains from the time when the universe was about 380,000 years old and has since cooled down due to the expansion.
Other supporting evidence includes the cosmological red shifts of distant galaxies, which are proportional to their distance from us, suggesting that galaxies are moving away from each other as the universe expands. This expansion is a fundamental observation predicted by the Big Bang theory and provides substantial support for it.