Can somebody please give me a little more detailed explanation of a simple Feynman diagram? It's not clear to me why the owner particle experience any force? Let's check out 2 electrons interacting by a virtual photon. 1) 1st e is moving along, throwing gazilions of virtual photons but nothing is happening yet to its momentum. Even when it throws the photon that eventually will reach 2nd e, nothing happening just yet, right? 2) A virtual photon of 1st e reaches the 2nd e and 2nd e got its momentum changed. Q: At which point 1st e got its momentum changed? I see several scenarios - please tell me which one is the correct one. a) at the moment when the photon is thrown by 1st e (despite this photon - like gazilions of other virtual photons thrown by this e - didn't interact with 2nd e yet, the 1st e somehow knows that it will, so, no point to loose time - that's QM for you!); b) after the photon will interact with 2nd e, 1st e will somehow instantaneously know it happened and will turn away; c) after the photon will return back to the 1st e; d) this process doesn't affect 1st e; it's up to 2nd e to throw another photon and hit 1st e to change 1st e momentum. Then 2 photons are needed to push 2 e away from each other. e) your version. Thanks.