Isomorphism between groups and their Lie Algebra

In summary, the question asks if an isomorphism between two groups also implies an isomorphism between their respective Lie algebras. The person believes that since the tangent spaces are mapped to each other and the Lie algebra is based on the tangent space, the Lie algebra should also be isomorphic. They use the example of SU(2) x SU(2) ≈ SO(4) and su(2) x su(2) ≈ so(4) to support their idea. However, it is important to note that while an isomorphism between two groups will result in an isomorphism between their Lie algebras, the converse is not always true. The groups must also be locally diffeomorphic at
  • #1
raopeng
86
0
I must apologize if this question sounds dump but if an isomorphism is established between two groups, is it true that their lie algebra is an isomorphism too? My idea is that since the tangent space is sent to tangent space also in the matrix space, both groups' lie algebra will be isomorphism also. For example we have: SU(2) × SU(2) ≈ SO(4) and su(2) × su(2) ≈ so(4).
 
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  • #2
Hi raopeng,

Could you explain a little bit more?

Best regards

GoodSpirit
 
  • #3
For example we have an isomorphism between two groups, and we know that Lie Algebra of a group is the commutator of matrix of its tangent space at the identity. So if there exists an isomorphism, wouldn't that entail that, since the tangent space is sent to tangent space under the mapping, their lie algebra is isomorphic too? I have this idea when trying to establish an isomorphism between su(2) x su(2) ≈ so(4) and there is an isomorphism between SU(2) x SU(2) ≈ SO(4)
 
  • #4
A lie group isomorphism f between lie groups G and H will have full rank, so that the corresponding map between lie algebras df is an isomorphism. However, the converse is false, two lie groups can have the same lie algebra but be non isomorphic lie groups.
Groups that are locally diffeomorphic at the identity will have isomorphic lie algebras
 
  • #5
raopeng said:
I must apologize if this question sounds dump but if an isomorphism is established between two groups, is it true that their lie algebra is an isomorphism too? My idea is that since the tangent space is sent to tangent space also in the matrix space, both groups' lie algebra will be isomorphism also. For example we have: SU(2) × SU(2) ≈ SO(4) and su(2) × su(2) ≈ so(4).

you need to show that df[X,Y] = [df(X),dfY)] which implies that the linear isomorphism of left invariant vector fields is a Lie algebra homomorphism.
 

1. What is isomorphism between groups and their Lie algebra?

Isomorphism is a mathematical concept that describes a one-to-one correspondence between two structures. In the context of groups and Lie algebras, it refers to a relationship between the abstract algebraic structure of a group and the linear algebraic structure of its associated Lie algebra. This means that for every operation performed on the group, there is a corresponding operation on the Lie algebra that preserves the same structure.

2. What is the significance of isomorphism between groups and their Lie algebra?

The isomorphism between groups and their Lie algebra is significant because it allows us to study the properties of a group through its associated Lie algebra, which is often easier to work with. Additionally, it helps us to connect the abstract concepts of group theory with the more concrete concepts of linear algebra, providing a powerful tool for understanding both fields.

3. How is isomorphism between groups and their Lie algebra established?

To establish isomorphism between a group and its Lie algebra, we first need to define a mapping between the elements of the group and the elements of the Lie algebra. This mapping should preserve the group operation, meaning that if we apply the group operation to two elements, their corresponding elements in the Lie algebra should also satisfy the same operation. Once this mapping is established, we can then show that it is a bijective mapping, meaning that every element in the group has a unique corresponding element in the Lie algebra.

4. Can all groups and their Lie algebras be shown to be isomorphic?

No, not all groups and their Lie algebras are isomorphic. In fact, there are many groups that do not have a corresponding Lie algebra, and vice versa. Additionally, even if a group and its Lie algebra are isomorphic, there may be multiple ways to establish this isomorphism, as there can be different mappings between the elements of the group and the elements of the Lie algebra that still preserve the group operation.

5. What are some applications of isomorphism between groups and their Lie algebra?

The isomorphism between groups and their Lie algebra has numerous applications in mathematics and physics. In mathematics, it is used to study the structure and properties of groups, as well as to classify different types of groups. In physics, it is used to study the symmetries of physical systems, such as in quantum mechanics and particle physics. It is also used in the development of Lie group and Lie algebra-based methods in differential geometry and mathematical physics.

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