Since the four forces are a "closed list", one of them should be present in each interaction and, according to Standard model, a boson or mediating particle should be doing the job of the relevant force. For instance, the photon is the mediating particle of electromagnetic force. In turn, electrostatics seems to fall within the domain of electromagnetic force and hence the photon should be doing all jobs in this area. But is it really so? If I have an electron and 1 meter away a proton, they attract each other. Does that mean that a photon is travelling between the two particles? I would tend to think "no", but then I don't know what to do with the statement of the first paragraph.