Orientability of Null Submanifold w/ Boundary - Stokes' Theorem

In summary, the conversation discusses the possibility of defining an orientation for a null submanifold with boundary, and if it is possible to use Stokes' theorem in this case. It is mentioned that orientability and volume forms are topological and not affected by the metric, and that Stokes' theorem still holds. However, there may be issues with curvature and integrands that are nonscalar.
  • #1
ifidamas
3
0
I have this question: Is it possible to define an orientation for a null submanifold with boundary?
In that case, is possible to use Stokes' theorem?
In particular, there is a way to define a volume form on that submanifold?
 
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  • #2
Orientability is topological. Volume forms only depend on affine structure. None of these notions are metrical, so it doesn't matter if the metric is degenerate on your submanifold. Stokes' theorem still holds. There is a good discussion of this sort of thing at the end of ch. 2 of the free online version of Carroll, http://arxiv.org/abs/gr-qc/?9712019 .

The only thing to worry about is that if there's curvature and the integrand is nonscalar (e.g., the flux of stress-energy), then this sort of thing fails, because we can't even define unambiguously what it means to add vectors that lie in different tangent spaces.
 
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  • #3
So I can't integrate a 2-form over a 2-submanifold which is a boundary of a nulla 3-submanifold?
 

FAQ: Orientability of Null Submanifold w/ Boundary - Stokes' Theorem

1. What is the definition of an orientable null submanifold with boundary?

An orientable null submanifold with boundary is a subset of a higher dimensional space that is locally flat and has a well-defined orientation. This means that at each point on the submanifold, there is a consistent way to define a direction and a consistent way to determine whether a vector is pointing in that direction or its opposite.

2. How is the orientability of a null submanifold with boundary related to Stokes' Theorem?

Stokes' Theorem is a fundamental mathematical concept that relates the integral of a differential form over a manifold to the boundary of that manifold. In the case of an orientable null submanifold with boundary, Stokes' Theorem states that the integral of a differential form over the submanifold is equal to the integral of the same form over the boundary of the submanifold.

3. What is the significance of orientability in mathematics?

Orientability is significant in mathematics because it allows for the consistent definition of concepts such as vector fields, differential forms, and integrals. It also has important applications in various branches of mathematics, including topology, geometry, and differential equations.

4. Can a null submanifold with boundary be both orientable and non-orientable?

No, a null submanifold with boundary can only be either orientable or non-orientable. An orientable submanifold has a well-defined orientation at each point, while a non-orientable submanifold does not. It is not possible for a submanifold to have both properties simultaneously.

5. How can the orientability of a null submanifold with boundary be determined?

The orientability of a null submanifold with boundary can be determined by looking at the behavior of its tangent vectors. If the tangent vectors can be consistently oriented at each point, then the submanifold is orientable. If the tangent vectors cannot be consistently oriented, then the submanifold is non-orientable.

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