Big bang theory is the most accepted theory of evolution of the universe. According to this theory, the universe evolved due to the explosion which took place around 13.7 billion years ago. Various celestial bodies were produced by the substances which were emitted by the explosion. Due to the deposit of these substances around the bodies, they increased in size and several galaxies were formed, due to which, the universe started expanding. Since the time of its formation, the universe is continuously expanding.
