The Big Bang model is a theory about the early development of the universe.
The Big Bang theory says that the Universe was once in an extremely hot and dense state and this expanded rapidly (this is known as big bang). This Big Bang or the rapid expansion caused the young universe to start cooling down and resulted in the formation of the presently state of the universe.
According to measurements, the Big Bang occurred about 13.7 billion years ago. The Big Bang theory was proposed by Georges Lemaitre. He called his theory