“Our visible Universe is almost entirely composed of matter, and very little antimatter has existed since the Big Bang in which the Universe was born. When an antiparticle meets its particle counterpart, they annihilate, converting all of their rest mass into energy. Antiparticles can be made out of energy in the reverse of this process, but only if a particle counter part for every antiparticle is produced as well. This happens naturally in high-energy processes involving cosmic rays, and also in high-energy experiments in accelerators on Earth. Because the world is overwhelmingly made of matter, however, any antiparticle produced in this way soon meets up with a particle counterpart and annihilates.” John Gribbin