# Math courses for next semester.

1. Oct 15, 2004

### gravenewworld

Can someone please tell me what Lie Algebra is all about in a simple manner, I am not a PhD mathematician. I am trying to decide what I should do my independent study on next semester. I was thinking of studying an introduction to Lie Algebra or Mathematical Logic. Which of the two would be better to study? Any recommendations? Which branch is used more? Opinions? Thanks.

2. Oct 15, 2004

Staff Emeritus
First of all a Lie algebra is an algebra. That is it is a vector space with a product. The product is a special kind often represented by a bracket [x,y], which takes two vectors and spits out another vector. And it has the key property that [x,y] = -[y,x] for all x and y. So the Lie algebras are all anticommutative. Another property the product has is the Jacobi identity: [x,[y,z]] + [y,[z,x]] + [z,[x,y]] = 0.

Lie algebras arise from Lie groups. Every Lie group is a manifold and it has a tangent space. And the local tangent space (the fiber) over the group identity is uniquely defined as a Lie algebra. The tangent space is spanned by a set of basis vectors $$X^a$$ and the product is given by $$[X^a,X^b] = f^{ab}_cX^c$$, where the f 's are numbers determined by the group. By studying the Lie algebra you can find out things about the group. Often in physical situations where they have a group (such as a gauge group), they find it easier to work with the Lie algebra.

Lots of standard results about which common Lie groups have which Lie algebras. The group only has one Lie algebra, but the same Lie algebra can come from more than one group.

A lot of any course in Lie algebras consists of ways to classify them. This gets into Dynkin diagrams which are almost magical in some ways - John Baez just loves them - but which I am NOT going to get into here!

3. Oct 15, 2004

### fourier jr

Maybe I should say I'm planning to do set theory as directed studies (there's no regular course on that) next term because it's close to the foundations. That is, stuff like Zorn's lemma (& its equivalents) are used all throughout analysis, algebra, etc; Dedekind cuts & transfinite arithmetic, etc have been mentioned in courses up to this point also, so I think it would be good to do some of that stuff too. I think it would really help me because sets are so fundamental to those areas. Now guess which course, out of mathematical logic or Lie algebras, I'd pick if I had to pick only one...

I'm more interested in pure math though; if you're more interested in applied math or physics I would say Lie groups/algebras over mathematical logic since Lie groups/algebras are used a lot in quantum mechanics. (from what I've heard; I think it has something to do with symmetry)

Last edited: Oct 15, 2004