How are groups with the same Lie Algebra inequivalent?

862 Views Asked by At

I thought that groups with the same Lie Algebra are automatically equivalent, but there appear to be some exceptions to this?

What sort of exceptions are there and why?

1

There are 1 best solutions below

3
On BEST ANSWER

The 3-sphere (unit quaternions) and SO(3) have the same Lie algebra. Why? Because one is a double cover of the other, and the Lie algebra can be defined purely locally (via vector fields, for instance).

So I guess a general answer is "covering groups are a general case where same algebra doesn't (necessarily) mean same group."

(Sometimes you get a covering group that IS isomorphic, as in the covering $\theta \mapsto 2\theta$ on $S^1$.)