I am currently reading The Elegant Universe by Brian Greene and have a question about a topic in it. On p.9 he is talking about muons, electrons, positrons, and all that other good stuff. He explains that when particles and their anti-particles come into contact with eachother, they "annihilate" one another. He then goes on to say that everything in the universe is made up of these particles and their anti-matter particles. My question is as follows: If the particles and their anti-matter particles annihilate one another upon contact, how could something in the universe have a particle and its anti-partner in the same "thing"? Wouldn't they just annihilate eachother and therefore wouldn't be around in the "thing" anymore? I know I am probably missing something really obvious, but humour me anyway. p.s. If you have the book on you, like I said before, it is on page 9 (along with a chart). Thanx in advance.