The Big Bang theory states that the universe began as a singularity, an extremely dense and hot point, about 13.8 billion years ago. During this event, the universe rapidly expanded, cooled, and matter began to form. Over time, atoms and galaxies formed as the universe continued to expand. The theory also accounts for the observed redshift of galaxies, cosmic microwave background radiation, and the abundance of light elements, all of which provide evidence for the expansion and evolution of the universe.
