The Big Bang Theory The Big Bang Theory is a widely-accepted cosmological model that describes the initial expansion and subsequent evolution of our universe. Initial Singularity The Big Bang Theory, as its name suggests, begins with an explosive event: the Initial Singularity. A moment roughly 13.8 billion years ago when the entire universe was confined to a point of infinite density and temperature. In an instant, this singularity expanded, giving birth to space, time, matter, and energy as we understand them today. Expansion of the Universe The Big Bang Theory postulates that the universe