How can an exchange of a photon describe the attractive force between two objects with opposite charge?
Well, think again about two people standing in two different boats. Now imagine them standing with their backs turned toward each other, and one person is throwing a boomerang. Throwing the boomerang this person will move towards the other boat as he gets a push against the direction he threw the boomerang. The boomerang, being in the air, flies a curve, and it will eventually arrive at the person in the second boat. Catching the boomerang this person will now be pushed towards the person that threw the boomerang, and they both move closer to each other, they “attract” each other. Summary: A photon can act either as a basketball or as a boomerang, depending on the charges of the two objects that exchange that photon.
