Does a Compact Manifold Imply a Compact Tangent Bundle?

In summary, the conversation discusses the compactness of tangent bundles on a compact manifold. It is concluded that tangent bundles cannot be compact and one way to make them compact is by replacing them with the bundle PTX, whose fibers are projective spaces. It is also mentioned that projective spaces are compact.
  • #1
math6
67
0
hello friends
my question is: if we have M a compact manifold, do we have there necessarily TM compact ?
thnx .
 
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  • #2
Of course not. Just loot at one tangent space. On the one hand, that's closed in TM, and on the other hand its homeomorphic to R^n (not compact). So TM cannot be compact, otherwise each tangent space would be too.
 
  • #3
one way to make it compact is to replace TX by PTX, the bundle whose fibers are the projective spaces associated to the tangent vector spaces.
 
  • #4
thnx for answers are you sure mathwonk for the answers can you give me proof if you can please ?
 
  • #5
mathwonk said:
one way to make it compact is to replace TX by PTX, the bundle whose fibers are the projective spaces associated to the tangent vector spaces.

Aren't those the tautological bundles.?
 
  • #6
Never mind, Wonk, I spoke too soon, there is just a vague relation.
 
  • #7
Math6:
I am not sure I understood your question, but Projective spaces are compact
because they are the continuous image ( under the quotient map) of the
compact space S^n, and so they are compact.
 

Related to Does a Compact Manifold Imply a Compact Tangent Bundle?

Question 1:

What is a compact manifold?

A compact manifold is a type of mathematical space that is both smooth and finite in size. It is a generalization of a surface in 3-dimensional space, and can have any number of dimensions. In simpler terms, it is a curved space that is finite and smooth.

Question 2:

What is a tangent bundle?

A tangent bundle is a mathematical construction that describes the set of all possible tangent vectors at every point on a manifold. It is essentially a collection of all the possible directions in which a manifold can be locally deformed.

Question 3:

Does a compact manifold always imply a compact tangent bundle?

No, a compact manifold does not always imply a compact tangent bundle. In fact, there are examples of non-compact manifolds that have compact tangent bundles. This is because the compactness of a manifold only depends on its global structure, while the compactness of a tangent bundle depends on its local structure.

Question 4:

What is the significance of a compact tangent bundle?

A compact tangent bundle has important implications in the study of differential geometry and topology. It allows for the application of powerful mathematical techniques and theorems, and can provide insight into the global properties of a manifold. In essence, a compact tangent bundle simplifies the study of a manifold and allows for a deeper understanding of its structure.

Question 5:

How do we prove that a compact manifold implies a compact tangent bundle?

To prove that a compact manifold implies a compact tangent bundle, we can use the fact that a manifold is a locally compact space. This means that every point on a manifold has a compact neighborhood. By constructing a suitable partition of unity, we can show that the tangent bundle is also locally compact, and hence, compact. This proof technique is known as the 'Whitney embedding theorem'.

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