Physicists have identified 57 distinct species of elementary particles and have determined many of their properties in exquisite detail. What are their roles? How will we know when we have found them all? Perhaps these particles are just different notes on a single superstring. Perhaps they are related by grand unification, or other hidden symmetries, in ways that we have yet to decipher. Unification may provide the key, the simple principle that gives particles their complex identities.
The Birth of the Universe