What theory states that the universe began in a violent explosion?

The theory that states that the universe began in a violent explosion is the Big Bang Theory.

Explanation:

The Big Bang theory is the predominant cosmological model for the oldest known periods of the universe and its subsequent large-scale evolution, which states that the universe was in a very high density and temperature state and then expanded through an explosion. Modern measurements date this time approximately 13.8 billion years ago, which would be the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles and later simple atoms. Giant clouds of these primordial elements joined later due to gravity, to form stars and galaxies.