Mainstream cosmology is the scientific study of the universe's origin, evolution, and structure. It is primarily based on the Big Bang theory, which suggests that the universe began as a singularity approximately 13.8 billion years ago and has been expanding ever since. This field combines observations from astronomy, physics, and mathematics to understand cosmic phenomena. Key concepts in mainstream cosmology include dark matter and dark energy, which are believed to make up most of the universe's mass-energy content. Cosmic microwave background radiation provides evidence of the early universe, while the Hubble Law describes the relationship between distance and the speed at which galaxies are receding from us.