The LHCb collaboration at CERN has announced the discovery of a new exotic particle: a so-called “tetraquark”. The paper by more than 800 authors is yet to be evaluated by other scientists in a process called “peer review”, but has been presented at a seminar. It also meets the usual statistical threshold for claiming the discovery of a new particle. The finding marks a major breakthrough in a search of almost 20 years, carried out in particle physics labs all over the world. To understand what a tetraquark is and why the discovery is important, we need to step back in time to ....