Why Is There Matter?

If a particle and an antiparticle meet, they disappear by emitting two photons or a pair of some other particles. In the primordial soup that existed after the Big Bang, there were almost equal amounts of particles of antiparticles, except for a tiny asymmetry: one particle per 10 billion. As the universe cooled, the particles and antiparticles annihilated each other in equal numbers, and only a tiny number of particles remained; this tiny amount is all the stars and planets, and gas in today’s universe.

~ Alexander Kusenko (1966-03-01 age:51)