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For example, one electron can deflect another when the two exchange a photon, so the simplest Feynman diagram for the process consists of two lines representing the electrons and a wavy line connecting them that represents the photon.

A pictorial representation of this process, known as a Feynman diagram, is shown in Fig. 1a.

Barr’s book, then, is a portrait of a pivot, a sumptuous record of an encounter not unlike those particle interactions depicted in a Feynman diagram in which the participants approach each other, glow furiously for an instant, and then depart the scene utterly changed.

Therefore, the Feynman diagram, becomes the tool for turning extremely complicated field-theoretical mathematics developed by another physicist into more intuitive forms of computation by embedding some of the more complicated mathematical mechanism in the vertices of the diagram. 

The Feynman diagram serves as a catalyst for understanding the calculations, processes, and microstate interactions involving the physical building blocks of nature through space and time, while also representing a visual actualization of ‘virtual’ and ‘real’ particles.