The name of the theory that explains how the universe began is the Big Bang theory. This cosmological model proposes that the universe originated from an extremely hot and dense state approximately 13.8 billion years ago. It subsequently expanded, cooling down and forming subatomic particles, atoms, and eventually galaxies. The Big Bang theory is supported by various empirical evidence, including the cosmic microwave background radiation and the observed redshift of distant galaxies. This theory fundamentally reshapes our understanding of the universe’s evolution and its current structure.