ELI5: Explain Like I'm 5

Root system of a semi-simple Lie algebra

Alright kiddo, do you remember learning about numbers and how we can think of them as either prime or composite? A similar idea applies to Lie algebras, which are mathematical objects that help us study symmetry in geometry and physics.

A Lie algebra is called semi-simple if it cannot be broken down further into smaller Lie algebras that still carry meaningful information. The root system of a semi-simple Lie algebra is a special set of vectors that gives important clues about the algebra's structure and symmetry.

Just like how each number has a unique set of factors, the vectors in a root system have certain relationships with each other that make them "prime" to the algebra. These relationships are described by a graph called a Dynkin diagram, and they help us understand how the roots can combine and transform under different symmetries.

Overall, the root system is a really important tool for studying semi-simple Lie algebras, sort of like how a map helps us navigate a new city. Hopefully that helps explain it!