Sometimes, the electric force between two electrically charged particles is explained by the analogy of two freely floating astronauts that start throwing a ball towards each other. In this analogy, momentum is transferred from the astronaut to the ball which causes the astronaut to move in the opposite direction than the ball. Similarly, the astronaut who catches the ball picks up that momentum and therefore also moves away from the other astronaut.
The same argument is then made for the repulsion of two alike electric charges: they exchange virtual photons which carry momentum and transfer it from one charge onto the other causing them to move away from each other. This makes sense until one considers opposite charges which attract each other. But the mechanism of exchanging virtual photons is the same and since each photon carries momentum which must be compensated by the emitting particle, how can the attraction of electric charges be explained by the exchange of virtual photons?
