human
Explain the concept of the Big Bang Theory?
assistant
The Big Bang Theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. The model describes how the universe expanded from a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background, large-scale structure, and Hubble's law. The Big Bang is thought to have occurred approximately 13.8 billion years ago, which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles and later simple atoms. Giant clouds of these primordial elements would eventually coalesce within regions of slightly higher density, forming stars, galaxies, and everything else seen today.