# Strong force as exchange of mesons, or of quark and antiquark

• I
The (residual) strong force between nucleons can be desribed as

- The exchange of a meson (from a nucleon to the other), as in picture b)
- The exchange of a quark and an antiquark: in picture a) one nucleon "gives" a quark and receive an antiquark and it's the opposite for the other

I do no see how these two description are consistent with each other since in picture b) the meson (a quark + an antiquark) goes from one nucleon to the other, while in a) there is an exchange. So are these two interpretation equivalent? The nucleon that gives the quark also gives the antiquark (and therefore a meson) or receives it instead?

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mfb
Mentor
Same thing. You don't have an actual time axis anyway in these diagrams, only initial and final states.

Here is your meson going from left to right in the left diagram:

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crick
Same thing. You don't have an actual time axis anyway in these diagrams, only initial and final states.

Here is your meson going from left to right in the left diagram:

View attachment 227384

But there is actually a time axis and it is vertical (going from down to up). I'm aware that antiparticles move backwards in time (in the picture it moves downward a bit) but the fact is that it moves from left to right "in space".

Is this wrong? So actually (besides moving backwards in time) the direction in space indicated by the arrow in the feynman diagram should be reversed for an antiparticle?

Staff Emeritus
I'm aware that antiparticles move backwards in time

No they don't.

Klystron
mfb
Mentor
But there is actually a time axis and it is vertical (going from down to up).
The only meaningful times in a Feynman diagram are the initial and final states. Everything inside doesn't have a time ordering, and in fact you have to consider all times for all vertices for calculating such a diagram.