What does the Big Bang Theory explain?

The Big Bang Theory fundamentally describes the initial moments of the universe’s expansion from an extremely hot and dense state, referred to as a singularity. According to this theory, about 13.8 billion years ago, the universe began expanding rapidly. This expansion led to the cooling and eventual formation of various structures, such as galaxies, stars, and other cosmic entities over billions of years.

By focusing on the early development of the universe, the Big Bang Theory provides crucial insights into the conditions that existed right after the expansion began, including the formation of basic particles and the subsequent nuclear processes that led to the creation of hydrogen and helium—the building blocks for more complex structures. This understanding is foundational in cosmology, as it not only explains the observable phenomena we see today but also provides a framework for understanding the universe's evolution.

Other choices, while related to astronomical phenomena, address different aspects of cosmic science and are not directly explained by the Big Bang Theory itself. Each of those subjects—like the formation of stars, black holes, or comet lifecycles—requires different scientific explanations and is a product of processes that occur after the universe's initial expansion.