The Big Bang model or theory is the prevailing cosmological theory of the early development of the universe. According to the Big Bang model, the universe was originally in an extremely hot and dense state that expanded rapidly. This expansion caused the universe to cool and resulted in the present diluted state that continues to expand today. Based on the best available measurements as of 2010, the original state of the universe existed around 13.7 billion years ago, which is often referred to as the time when the Big Bang occurred. The theory is the most comprehensive and accurate explanation supported by scientific evidence and observations.