Question: Why do positive and negative charges attract?

Alessandro Guazzi answered on 12 Mar 2013:

Ooooh, really tricky one! In classical physics, this would be a non-question: opposite charges are *defined* such that they attract each other. In quantum physics, and in particular a field called quantum electrodynamics, the attraction of opposite charges and repulsion of like charges is explained by the exchange of virtual photons between the charges, and it is these virtual particles that carry the attractive force.