Feynman Diagrams

Before moving on, I thought I’d better go over Feynman diagrams (FD).  What they are, why we use them, and how to read them.

Richard Feynman thought them up to help explain in a visual manner of how particles interact.  He used them heavily in explain quantum electrodynamics in a simplified way.  The following picture is an example of a Feynman diagram.

Fig 1: This diagram in is showing, if i’m not mistaken, an electron (e^-) releasing a photon(γ), changing direction.  Then the photon gets absorbed in to a different election changing its momentum.

You can think of a FD as a 2d graph.  In a normal 2d graph, you would label the vertical axis Y, and the horizontal axis X.  In a FD, the vertical axis is usually time, and the horizontal axis is space.

In Fig 1, the first election starts out by moving to our right, then emits a photon and ends up moving to the left.  The electron on the right, starts out by moving to the left.  Then absorbs the photon and is now moving to our right.

This is actually an interesting thought.  In my last post, I mentioned that photons carry the electromagnetic force.  If you think about this diagram, all it’s showing is two electrons getting close together.  Then they repel, like two magnets.  The “repulsion” is carried by the photon!  Someone please correct me if I’m wrong, this is just how I understand it.

We’ve now seen a simple FD.  In the next post, we’ll see a more complex one while I try to explain beta decay of a neutron in to a proton.