[Physics] What do the arrows on this Feynman diagram represent?

antimatterelectronsfeynman-diagramsquantum-electrodynamics

The picture follows the convention of the time axis being on the vertical direction.

I think this Feynman diagram represents Coulomb repulsion between two electrons with a virtual photon being absorbed and emitted by each electron.

What are the arrows on the electron lines for? I'm not sure what information this tells us.

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Best Answer

They tell you whether they're electrons or antielectrons (positrons). The convention is that if the arrow points the same direction that time flows then it's an electron, and if it points the opposite direction then it's a positron. In this case the arrows point in opposite directions so one particle's an electron and the other's a positron and the process represents an attraction, although knowing which is which requires specifying whether time flows upward or downward.