explanation for "Incompatibility with special relativity and momentum conservation"? Can anyone provide an explanation for this claimed contradiction between basic electromagnetism and momentum conservation? (Sorry, as a new member I can't post links.) News article: "Textbook Electrodynamics May Contradict Relativity" at by Adrian Cho at Science, DOI 10.1126/science.336.6080.404 Corresponding arXiv submission: 1205.0096 "Trouble with the Lorentz law of force: Incompatibility with special relativity and momentum conservation" The lower half of the figure in the news article explains the idea better than I can in words; to see a copy of the figure, go to the imgur page xrDXb. In the lower left of the figure the net force should be zero. However, the lower right corresponds to the same setup viewed by a moving observer, and there seems to be a torque that arises.