Asked by: Miguel Angel de Blas

Feynman realized that the somewhat lengthy sums of integrals can be conveniently summarized as a sum of diagrams. The diagram acts like a recipe: take these incoming particles, have them annihilate into some intermediate particle, and then have this intermediate particle decay into some final state particles. Integrate over the intermediate particle's momentum and impose energy/momentum conservation. The graphical shorthand is very convenient and appeals to our intuitive sense that physics is local -- interactions occur when particles are at the same spacetime point (the vertices in a Feynman diagram), like billiard balls bouncing off one another. A nice graphical description of these things is provided at: http://www2.slac.stanford.edu/vvc/theory/feynman.html.

As for a bibliography, QED can be found in all quantum field theory textbooks. You can read some non-technical books such as Feynman's own 'QED: The Strange Theory of Light and Matter,' or 'QED and the Men Who Made It' by S. Schweber.

Very introductory descriptions of particle physics, quantum field theory and general Feynman diagrams can be found in: Introduction to High Energy Physics, D. Perkins Introduction to Elementary Particles, D. Griffiths

A mid-level treatment is given in Quarks and Leptons: An Introductory Course in Modern Particle Physics, by F. Halzen and A. Martin.

The standard references for graduate students are Relativistic Quantum Fields, by Bjorken and Drell Introduction to Quantum Field Theory, by M. Peskin and V. Schroeder

Answered by: Brent Nelson, M.A. Physics, Ph.D. Student, UC Berkeley

'There comes a time when the mind takes a higher plane of knowledge but can never prove how it got there. All great discoveries have involved such a leap. The important thing is not to stop questioning.'**Albert Einstein**

(*1879-1955*)