What is the significance of cosmic microwave background radiation?

The significance of cosmic microwave background radiation lies in its role as a critical piece of evidence for the Big Bang theory. This radiation is a faint glow that fills the universe and is recognized as the remnant heat from the hot, dense state of the early universe shortly after the Big Bang, when the universe began to expand and cool.

Around 380,000 years after the Big Bang, the universe had cooled sufficiently for protons and electrons to combine to form neutral hydrogen atoms, allowing photons to travel freely. This release of photons is what we observe today as cosmic microwave background radiation. It has a uniform temperature of about 2.7 K and is highly isotropic, meaning it appears almost the same in all directions of space. These characteristics support the idea that the universe has expanded from a hot, dense state, confirming theoretical predictions regarding the early universe.

In contrast, the other choices do not accurately capture the role of cosmic microwave background radiation. While phenomena like black holes and dark energy are important in astrophysics, they do not directly relate to this specific type of radiation or its implications for the universe's origins. The temperature of stars is also unrelated to this cosmic background radiation, as it pertains to stellar processes rather than the conditions of the early universe