If there was to be some cataclysm, and he could preserve just one sentence for future scientists, Richard Feynman would have made it about atoms. Tell them everything was made of tiny particles in constant motion, thought the great 20th-century physicist, attracting and repelling each other along the way. With a little imagination they could then uncover the rest. That was because the universe had a marvellous feature: though vast, it could be described by surprisingly few laws. Armed with the knowledge of atoms, Feynman reckoned his successors could work some of these out and then deduce far more.