Today, Physics accepts that matter and antimatter are attracted, with a force proportional to the electromagnetic force. The theory of the Big Bang [2], which is also the established theory for the creation of the Universe, is based on this assumption. According to the Big Bang theory, at the beginning of the creation, more matter than antimatter was created. So after the self-destruction between matter and antimatter, due to the strong attraction between them, a large amount of matter remained that created the Universe. In contrast to the Big Bang theory, the theory of the Chain Reaction [3], which is an alternative theory for the creation, accepts the opposite, namely that matter and antimatter repelled with a very weak force, opposite and proportional to the force of the attraction of two masses. So, according to the Chain Reaction theory, at the beginning of the creation, equal amounts of matter and antimatter were created, which, due to their repulsion, separated and matter created the Universe and antimatter the Antiuniverse. Maybe it was created, and many other Universes and Anti-universes. To date, no theoretical or experimental proof has been given by the established science to the acceptance that matter attracts antimatter. On the contrary, the author of this paper, who is also the author of the Chain Reaction theory, gives a clear proof that leads us to the conclusion that matter repels antimatter; at the same time he also calculates the force of this repulsion, which is equal but opposite to the force of the attraction of two masses.