The origin of the universe lies in the basics of the Big Bang theory which was proposed by Georges Lemaitre.
According to this theory, about 13.8 billion years ago, all the matter and energy in the universe were concentrated in an area smaller than an atom.
The phenomena such as the existence of light elements in abundance, the cosmic microwave radiation, the large-scale structure, and Hubble's law were explained on the basis of the Big bang theory.
The age of the universe is considered to be 13.8 billion years as it is believed that the big bang is the origin of the universe.