Feynman Diagrams in QED


The Feynman Diagrams were introduced by the great physicist Richard Feynman. He and 2 other physicist won the 1965 Nobel Prize for their groundbreaking work on QED.  but, it was the simplicity of Feynman’s work that made him special. you will realize this as you read further.

A Feynman diagram is a picture representation of equations that describe the interaction between electrons. When two electrons approach each other, their electromagnetic fields interact and they are pushed apart. It is known that these electromagnetic interactions happen via exchange of photons. Therefore, when two electrons approach, one electron releases a photon and the other absorbs it.

The Feynman Diagram

In this diagram, every line and vertex is just a part of an equation. the most simple Feynman Diagram is the one above where we have two electrons approaching each other and exchanging one photon. the equation of the diagram above can be given like this-

All straight lines represent an electron. The two lines which appear to be approaching each other are the incoming electrons. these two electrons are represented by i in the equation. The two straight lines which are moving apart depict the outgoing electrons and they are depicted by o in the equation. The wiggly line depicts the photon. it is represented by the variables in the middle bracket. the vertices are described by ie γ.

The most simple Feynman diagram is the most likely to happen. the probability of a specific Feynman diagram depends on the number of vertices in the diagram. for example in let the diagram above have a probability of 1. A Feynman diagram with 3 vertices will have a 1/100 probability of happening. A Feynman diagram with 4 vertices will have a probability of 1/100th of 1/100 or 1/10000. an example of a Feynman diagram with 4 vertices is shown below. It is a basically a diagram with two photon exchanges instead of one.

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