Piaw Na

“More important is that besides these four families, there are five “exceptional” Lie groups, named G2, F4, E6, E7, and the largest one, E8. And it can be proved that these are all the simple Lie groups there are, period. To appreciate how bizarre this is, imagine you visit a website where you can order door signs with numbers: 1, 2, 3, 4, and so on, all the way up to infinity. Then you can also order an emu, an empty bottle, and the Eiffel Tower. That’s how awkwardly the exceptional Lie groups sit beside the orderly infinite families.”
― Sabine Hossenfelder, Lost in Math: How Beauty Leads Physics Astray