The Big Bang Theory is a cosmological model that explains the origins and evolution of the universe. According to this theory, the universe started as a singularity, a point of infinite density and temperature, which rapidly expanded in a colossal explosion called the Big Bang. After the Big Bang, the universe began to cool down, and matter and energy started to clump together to form the first galaxies and stars. This process continued throughout billions of years of cosmic evolution, leading to the universe we see today. The evidence for the Big Bang comes from cosmic microwave background radiation, the observed abundance of light elements, and observations of the large-scale structure of the universe. Scientists continue to explore and refine the Big Bang Theory to better understand the universe and its origins.