Cut matter into ever-smaller pieces and you eventually hit rock bottom: a short list of truly fundamental particles — quarks, leptons, and the force-carriers that pass between them — that, as far as anyone can tell, are not made of anything at all. Particle physics is the quest to find that list and the rules it obeys, written up in the astonishingly accurate Standard Model.

This branch takes the intuitive Standard Model picture and puts it on a firmer footing: the symmetries and conservation laws that organise the particle zoo, Feynman diagrams as a bookkeeping for interactions, the electromagnetic, strong and weak forces, the Higgs mechanism, and the accelerators and detectors that test it all. It rests on quantum mechanics and special relativity.