Feynman diagrams are used to represent particle interactions. They are
made up of a series of vertices (interaction points) all of which involve three components.
The example shows a boson (shown blue) and two particle tracks. One of the particle tracks always points into the vertex and the other out of it. If a particle track points in the direction of time it is a particle (shown
orange), however if it is in the opposite direction it is an antiparticle (shown green).
By convention, time always progresses from left to right.