Feynman diagrams are used in quantum mechanics. A Feynman diagram has "lines" in different shapes—straight, dotted, and squiggly—which meet up at points called "vertices". The vertices are where the lines begin and end. The points in Feynman diagrams where the lines meet represent two or more particles that happen to be at the same point in space at the same time. The "lines" in a Feynman diagram represent the probability amplitude for a particle to go from one place to another.