Explain Big bang theory

Georges Lemaitre (1927) had proposed a model for origin of the universe which became the Big Bang theory. The Big Bang theory explains the origin of universe, with the key idea that the universe is expanding. In the past, the universe was denser and hotter. All of space was contained in a single point, which is considered the inception of the universe. After the initial expansion, the universe freezes that allowed the creation of subatomic particles, consisting of protons, neutrons, and electrons. The majority of atoms formed were hydrogen, along with helium and traces of lithium. Huge clouds of these primal elements later fused through gravity to form stars and galaxies. The massive elements were synthesized either within stars or during supernova. Hence, the Big Bang theory does not explain the initial condition of the universe, but instead it describes the general evolution of the universe.