Cayley's Theorem (isomorphisms of Cyclics to SN)

  • Thread starter ChrisVer
  • Start date
  • Tags
    Theorem
In summary, any finite group G with order |G| = N < \infty is isomorphic to a subgroup of the symmetric group S_N. This can be seen through examples such as the cyclic group of order three, which is isomorphic to the alternating group A_3. However, for other cases such as the cyclic group of order four, the subgroup of S_4 will not be isomorphic to the cyclic group, as the orders of the elements do not match. Additionally, the claim that the subgroups of S_4 will be the Klein 4-group is incorrect, as there are other subgroups such as the cyclic subgroup generated by the rotation of a square. This discussion may be better suited for the abstract algebra
  • #1
ChrisVer
Gold Member
3,378
464
Any finite group [itex]G[/itex] with order [itex]|G| = N < \infty [/itex] is isomorphic ([itex] \cong [/itex] ) to a subgroup of the symmetric group [itex]S_N [/itex].

I have one question here, let's take the cyclic group of order three: [itex]C_3 = \{ e, c, c^2 \} [/itex]. By Cayley's theorem, this should be isomorphic to some subgroup of [itex]S_3 [/itex].
The subgroups of [itex]S_3[/itex] are pretty definite, and they are also normal subgroups , created by the union of conjugacy classes. They are the [itex] \{ (.) \} [/itex] , [itex] S_3 [/itex] (both trivial) and the union of [itex] \{ (.) \} \cup \{ (...) \}[/itex] which is the Alternating group [itex]A_3 [/itex].

Is it correct to say then that [itex]C_3 \cong A_3 [/itex] ? the orders seem to match.On the other hand what happens if I go for example to [itex]C_4 [/itex] ? In that case the subgroups of [itex]S_4[/itex] will be:

1. [itex] \{ e \}[/itex]
2. [itex] S_4 [/itex]
3. [itex] \{ (.) \} \cup \{ (..)(..) \} \cong C_2 \times C_2 [/itex]
4. [itex] \{ (.) \} \cup \{ (...) \} \cup \{ (..)(..) \} \cong A_4[/itex]

My problem is that in this case, the only "order" which matches is the [itex]C_2 \times C_2[/itex], But I don't think that the Klein 4-group is isomorphic to the cyclic group, because the orders of the elements don't match. Any help?
 
Physics news on Phys.org
  • #2
are you familiar with cycle notation? isn't (1234) a cycle of order 4, generating a cyclic subgroup of S4 of order 4? e.g. take the subgroup of permutations of the 4 vertices of a square, generated by the rotations of the square about its center, through multiples of 90 degrees.

the problem seems to be with your claim: " In that case the subgroups of S4 will be:..."And you probably meant to post this in the abstract algebra section.
 

Related to Cayley's Theorem (isomorphisms of Cyclics to SN)

1. What is Cayley's Theorem?

Cayley's Theorem states that every finite group is isomorphic to a subgroup of the symmetric group on the same number of elements. In other words, every group can be represented by a permutation of its elements.

2. How does Cayley's Theorem relate to cyclic groups?

Cayley's Theorem shows that every cyclic group is isomorphic to a subgroup of the symmetric group. This means that every cyclic group can be represented by a permutation of its elements, just like any other finite group.

3. Can Cayley's Theorem be extended to infinite groups?

No, Cayley's Theorem only applies to finite groups. It cannot be extended to infinite groups because infinite groups do not have a finite number of elements to be permuted.

4. How is Cayley's Theorem useful in group theory?

Cayley's Theorem allows us to represent any finite group as a permutation group, which can make it easier to study and understand the structure of the group. It also allows us to prove certain properties and theorems about groups by using the properties of permutation groups.

5. Are there any limitations to Cayley's Theorem?

Cayley's Theorem only applies to finite groups and cannot be extended to infinite groups. It also does not provide a unique representation of a group, as there can be multiple ways to permute the elements of a group to represent it. Additionally, it does not tell us anything about the internal structure of a group, only its relationship to the symmetric group.

Similar threads

  • Linear and Abstract Algebra
Replies
1
Views
1K
  • Calculus and Beyond Homework Help
Replies
5
Views
1K
  • Linear and Abstract Algebra
Replies
1
Views
944
  • Set Theory, Logic, Probability, Statistics
Replies
27
Views
3K
  • Calculus and Beyond Homework Help
Replies
5
Views
2K
  • Calculus and Beyond Homework Help
Replies
4
Views
1K
  • Linear and Abstract Algebra
Replies
1
Views
1K
  • Calculus and Beyond Homework Help
Replies
1
Views
1K
  • Linear and Abstract Algebra
Replies
1
Views
2K
  • Linear and Abstract Algebra
Replies
8
Views
2K
Back
Top