In a recent piece for the New York Review of Books, Freeman Dyson reviewed Half-Life, a biography of Bruno Pontecorvo, a brilliant nuclear physicist and possible spy. Pontecorvo spent six years working on nuclear reactors in Canada, where he may or may not have passed information on to Soviet contacts. However, according to Dyson—who is himself a world-renowned mathematical physicist— even if Pontecorvo had been a spy, the overall effect of his information wouldn’t have been hugely important. Perhaps some of it might have been useful to Soviet bomb designers, but it wouldn’t have been a game changer. Furthermore, the Soviets already had two technical spies (Klaus Fuchs and Ted Hall) relaying information from Los Alamos.

This is where Dyson brings up an interesting distinction: that between technical and tactical spies. As a layperson, I’d always presumed a spy is a spy; however, in Dyson’s view, technical and tactical spies belong in entirely different categories. He…