Confused about particle interactions

[kelly0303]

Hello! As far as I understand, in QFT the interaction between particles is mediated by the exchange of a boson. When doing calculations, one assumes that you have 2 free particles coming in, they interact at a point by exchanging a boson and then they propagate again as free particles, and this is the image the Feynman diagrams show, too. However, (say in the case of 2 electrons) the interaction doesn't take place only once. The electrons feel the effect of each other all the time, so I would imagine that a diagram reflecting this should have a photon exchange at each point along the 2 electron lines. Is this continuous interaction mathematically equivalent to just one interaction at a given point? Or how should I think about the Feynman diagrams? Thank you!

 

[jtbell]

Feynman diagrams aren't spacetime diagrams that show particle trajectories. They're mnemonic devices in which each line and vertex corresponds to a factor in the calculation for the probability amplitude of the depicted process. The calculation actually integrates (in effect) over all the possible spacetime paths that the particles could take.

 

[haushofer]

You shouldn't take feynman diagrams too literally as depictions of what happens. They're merely calculational tools and besides that, qft only tells you what you can expect if you measure. It doesn't tell you ontologically what "really happens during the interaction".