‘Who ordered that?’ Isidor Rabi asked upon the discovery of the muon, a heavyweight cousin to the electron, in 1936. Physicists, still reeling from the twin blows delivered by Einstein’s theory of relativity and the rise of quantum mechanics, had dared to hope they had at least got a handle on the basic building blocks of the cosmos. The unexpected arrival of the muon gave the lie to that – and the muon was just the first of a whole bestiary of exotic particles to be identified over the following decades.
Eighty years later, physicists are still discovering particles at a handy clip but are hardly any closer to resolving the existential and phenomenological puzzles posed by the 20th-century revolutions in physics. Even as our knowledge of the materials of the universe has solidified, our understanding of its principles has remained nebulous. On a bad day, it can seem as if nothing is truly known, nothing is truly certain and nothing is what it seems.