Charlotte Higgins at The Guardian:
Rovelli’s work as a physicist, in crude terms, occupies the large space left by Einstein on the one hand, and the development of quantum theory on the other. If the theory of general relativity describes a world of curved spacetime where everything is continuous, quantum theory describes a world in which discrete quantities of energy interact. In Rovelli’s words, “quantum mechanics cannot deal with the curvature of spacetime, and general relativity cannot account for quanta”.
Both theories are successful; but their apparent incompatibility is an open problem, and one of the current tasks of theoretical physics is to attempt to construct a conceptual framework in which they both work. Rovelli’s field of loop theory, or loop quantum gravity, offers a possible answer to the problem, in which spacetime itself is understood to be granular, a fine structure woven from loops.
String theory offers another, different route towards solving the problem. When I ask him what he thinks about the possibility that his loop quantum gravity work may be wrong, he gently explains that being wrong isn’t the point; being part of the conversation is the point. And anyway, “If you ask who had the longest and most striking list of results it’s Einstein without any doubt. But if you ask who is the scientist who made most mistakes, it’s still Einstein.”