Q:

Feynman diagram and uncertainty

I have been introduced to the Feynman diagrams in QFT after following Wick-Dyson tedious formalism.
Two things are unclear, though, about the Feynman shortcut to compute scattering amplitudes.
What are the horizontal and vertical axes in these diagrams? Are they $x$ and $t$ respectively or $x$ and $y$?
If yes then we are drawing a particle with an exact momentun $p$.
But doesn't this violate the uncertainty principle since we are assuming exactly measured $x$ and $p$?

A:

There are no axes in Feynman diagrams. The only important part of a diagram is what is connected to what, and not the relative orientation. You can move around the pieces of a diagram and, as long as you don't break any line, the value of the diagram remains unchanged.

A:

You have to realize that the Feynman diagram is a schematic representation of the integrals of the scattering amplitude , necessary to calculate the integral for that order. All variables will be integrated within the limits of the integral, so it is not a real space and time but an iconic one seen in a Feynman diagram. The result is a crossection, or a lifetime for that interaction, or an angular distribution. Quantum mechanical probabilities are all there.

