This is a bit of a novice question I'm sure, but I was reading through Griffiths introductory particle physics text and in his section on QED, he states that the propagator of the photon is [tex]\frac{ig_{\mu \nu}}{q^2}[/tex] but I can't see where he gets this from. Where does the metric come from? Can someone explain this? It seems completely out of the blue. Thanks!(adsbygoogle = window.adsbygoogle || []).push({});

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Photon propogator = metric tensor?

**Physics Forums | Science Articles, Homework Help, Discussion**