What is Lie theory? Here is the big picture.

Part 4: (Work in progress, but it will be THE most important video of the series) A bird’s eye view on Lie theory, providing motivation for studying Lie algebras and Lie brackets in particular. Basically, Lie groups are groups and manifolds, and thinking about them as manifolds, we know that we want to understand Lie algebras; and thinking about them as groups, we know what additional structure we want on the Lie algebras - the Lie bracket. YouTube, please do not demonetise this video for me saying “Tits group”. This is an actual mathematical object named after a French mathematician Jacques Tits. Files for download: Go to and enter the following password: so3embeddedin5dim SO(3) embedded in R^5: (n-dim manifold can be properly embedded in R^(2n): if you only want “the overall picture”, but perhaps distances are distorted) (n-dim Riemannian manifold can be isometrically embedded in n(3n 11)/2 dim if compact, n(n 1)(3n 11)/2 dim if not compact: if you want everything to remain intact, i.e. distances are preserved) BCH formula (why Lie brackets are useful): –Campbell–Hausdorff_formula Finite simple groups as building blocks: Classification of finite simple groups: Levi decomposition (the more precise meaning of “building blocks” in Lie algebra): E8 (the monster group of Lie algebras): (mathematics) Video chapters: 00:00 Introduction 01:26 Lie groups - groups 05:41 Lie groups - manifolds 10:23 Lie algebras 14:16 Lie brackets 18:03 The “Lie theory picture“ Other than commenting on the video, you are very welcome to fill in a Google form linked below, which helps me make better videos by catering for your math levels: If you want to know more interesting Mathematics, stay tuned for the next video! SUBSCRIBE and see you in the next video! If you are wondering how I made all these videos, even though it is stylistically similar to 3Blue1Brown, I don’t use his animation engine Manim, but I use PowerPoint, GeoGebra, and (sometimes) Mathematica to produce the videos. Social media: Facebook: Instagram: Twitter: Patreon: (support if you want to and can afford to!) Merch: Ko-fi: [for one-time support] For my contact email, check my About page on a PC. See you next time!