The scientific theory that explains the origin of the universe is the Big Bang Theory. It posits that the universe began approximately 13.8 billion years ago from an extremely hot and dense singularity. Following this initial explosion, the universe has been expanding and cooling, leading to the formation of galaxies, stars, and planets. This theory is supported by various pieces of evidence, including the cosmic microwave background radiation and the observed redshift of galaxies. The Big Bang Theory has revolutionized our understanding of the universe's evolution and is a cornerstone of modern cosmology.