Proving 2^(1/3) is Not in Simple Field F: Tower Law and Attempted Solution

  • Thread starter 5kold
  • Start date
  • Tags
    Field
In summary, using the tower law and the fact that 2^(1/3) and 2^(2/3) are irrational, we can prove that 2^(1/3) is not in the field F.
  • #1
5kold
13
0

Homework Statement



Suppose F=Q(a_1,a_2,...,a_n) where a_i^2 is in Q for i=1,2,...,n. Prove that 2^(1/3)
is not in F.


The Attempt at a Solution



Someone suggested the tower law.. I have no idea what that is. Isn't this true because if 2^(1/3) was in F then 2^(2/3) must be in Q, but 2^(2/3) is irrational so it cannot be so 2^(2/3) is not in F. Is this right?
 
Physics news on Phys.org
  • #2


Your reasoning is correct. The tower law, also known as the field tower theorem, states that if F is a field and K is a subfield of F, then any intermediate field between F and K must also be a subfield of F. In this case, Q(a_1,a_2,...,a_n) is an intermediate field between Q and F, so if 2^(1/3) was in F, then 2^(2/3) must also be in F. However, as you pointed out, 2^(2/3) is irrational and therefore cannot be in Q, which contradicts the assumption that F contains only rational numbers. Therefore, 2^(1/3) cannot be in F. Great job on using logical reasoning to arrive at the correct conclusion!
 

FAQ: Proving 2^(1/3) is Not in Simple Field F: Tower Law and Attempted Solution

What is the significance of proving that 2^(1/3) is not in the simple field F?

The simple field F is the smallest field that contains all algebraic numbers. Therefore, if 2^(1/3) is not in F, it means that it cannot be expressed using a finite combination of rational numbers and basic arithmetic operations. This has important implications in algebraic number theory and abstract algebra.

What is the Tower Law and how does it relate to this problem?

The Tower Law, also known as the Tower Property, states that the degree of a field extension is equal to the product of the degrees of its intermediate fields. In other words, if F is an intermediate field between K and L, then the degree of the extension [L:F] is equal to [L:K] * [K:F]. This law plays a crucial role in understanding and proving the non-existence of certain algebraic numbers in a given field.

How is 2^(1/3) attempted to be expressed in the simple field F?

One possible way to express 2^(1/3) in the simple field F is by using the Tower Law repeatedly. We can first express 2^(1/3) as a root of a polynomial of degree 2 over the field Q, then express that polynomial as a root of a polynomial of degree 3 over the intermediate field Q(2^(1/3)), and so on. However, this method ultimately fails to express 2^(1/3) in F, proving its non-existence in the field.

Can the non-existence of 2^(1/3) in the simple field F be proven using other methods?

Yes, there are other methods to prove the non-existence of 2^(1/3) in F. One such method is using the fact that F is a perfect field, meaning that all irreducible polynomials over F are separable. Since the minimal polynomial of 2^(1/3) over F is not separable, it cannot be an element of the field, thus proving its non-existence.

Can this problem be generalized to other irrational numbers?

Yes, this problem can be generalized to any irrational number that is not algebraic over F. In other words, any number that cannot be expressed as a root of a polynomial with coefficients in F. However, the specific methods and techniques used to prove the non-existence of each number may vary.

Back
Top