In the universe, electromagnetic phenomena are broken down into three basic actions:

1. An electron goes from place to place
2. A photon goes from place to place
3. An electron absorbs or emits a photon

That's it! The combination of these simple events on a large scale describe everything from rainbow oil slicks to your eyeglasses. Feynman created his diagrams as a notation for these events. In a Feynman Diagram, electrons are solid lines, photons are squiggly lines and anything traveling at the speed of light ( c ) is depicted at a 45 deg. angle.

This image is Figure 63 from Feynman's book QED: The Strange Theory of Light and Matter. Each of the diagrams depicts what can happen when we begin with a photon and an electron, and we end with a photon and an electron. (a) shows the obvious absorbtion of the photon and subsequent emission of the photon. (b) shows something more interesting where the photon is actually emitted before it is absorbed. (c), however, is my favorite. Here, the electron travels along merrily and emits the photon, then travels back in time to absorb the photon! This type of event is not a simple theoretical construction, it is observed in the real world quite often! In observation, an electron traveling backwards in time is called a positron. The observed event (c) looks to us like the photon decays into an electron-positron pair, the positron meets up with the "first" electron and anihillates into a photon. What we seem to think are three separate particles (2 electrons and a positron) are simply the same single electron zipping around absorbing and emitting photons!

Now if we can only find some way of decoding information about the future from the positrons...