Real Numbers Vector Space: Countability of Basis

In summary, the conversation discusses the concept of a vector space with an infinite number of dimensions using the set of real numbers over the field of rational numbers as an example. The participants question why the basis of this vector space is not countable, and consider the implications of a countable basis. They conclude that if the basis and coefficients are both countable, the number of possible vectors would also be countable, which contradicts the infinite dimensionality of the vector space.
  • #1
leon8179
2
0
I know that the set of real numbers over the field of rational numbers is an infinite dimensional vector space. BUT I don't quite understand why the basis of that vector space is not countable. Can someone help me?
 
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  • #2
Suppose the basis is countable, what can you conclude from this?
 
  • #3
the span of a countable set is still countable? so R over Q does not have a countable basis, right?
 
  • #4
If you have n basis vectors and m possible coefficients then you can only make m*n vectors. Since Q is countable, the number of possible coefficients is countable: [itex]\aleph_0[/itex]. If the number of basis vectors were also countable, the number of vectors would have to be [itex]\aleph_0\times \aleph_0= \aleph_0[/itex]: countable.
 

1. What is a real number vector space?

A real number vector space is a mathematical concept that describes a set of objects, called vectors, that can be added together and multiplied by real numbers. This set must also follow certain rules, such as closure under addition and scalar multiplication, to be considered a vector space.

2. What does it mean for a basis to be countable?

A basis is a set of vectors that can be used to represent any vector in a vector space through linear combinations. If a basis is countable, it means that the set has a finite or infinite number of elements that can be counted in a one-to-one correspondence with the natural numbers.

3. How do you determine if a basis for a real number vector space is countable?

If the basis is finite, then it is automatically countable. To determine if an infinite basis is countable, we can use the concept of cardinality. If the basis has the same cardinality as the set of natural numbers, then it is countable.

4. What is the significance of a countable basis in a real number vector space?

A countable basis in a real number vector space means that the vector space has a finite or countably infinite number of dimensions. This is important because it allows us to understand and analyze the properties and behavior of the vector space more easily.

5. Can a basis for a real number vector space be uncountable?

Yes, a basis for a real number vector space can be uncountable. This means that the vector space has an uncountably infinite number of dimensions. However, such vector spaces are more complex and difficult to analyze compared to those with a countable basis.

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