We explore consequences of a hypothetical difference between active charges, which generate electric fields, and passive charges, which respond to them. A confrontation with experiments using atoms, molecules, or macroscopic matter yields limits on their fractional difference at levels down to ${10}^{-21}$, which at the same time corresponds to an experimental confirmation of Newton’s third law.

• Received 21 April 2006

DOI:https://doi.org/10.1103/PhysRevA.75.052104