From what I understand, the forces of nature are carried by, well, force-carrier particles like photons and gluons. So, when a proton and electron are attracted to each other by the electrostatic force, it’s caused by exchanging photons (?).
I don’t see how this works. To use a macroscopic analogy, which I know is dangerous when considering quantum systems, if you and I were tossing a ball back and forth, we would not feel a force pulling us closer together. Why is it that by exchanging force carrier particles, other particles feel an attraction?
Or, is it that this is as deep as we can probe with our current technology, and the theory agrees with experimental results, so life is good?
More to the point, a virtual photon can have a momentum in the opposite direction to its motion.
But you’re also correct that the classical analogy is inherently flawed. A pair of electrons can exchange a single photon, or two photons, or three photons, or ten million photons. So how many do they actually exchange? All amounts at once. In the same sense that the single-photon process is “really occurring”, so are all of the other processes, too.
(and I switched from a proton and electron to two electrons because the case with the proton is actually even more complicated.)
To make the subject both easier and harder to understand consider this: The wave nature of a virtual photon is everywhere at once, and as Chronos says can have its momentum vector pointing in whatever direction is consistence with the charge of the particle.
This, similar to entanglement, at first appears to violate SR, but since no information can be transmitted it really doesn’t.