Metric tensor derived from a geodesic

In summary, the conversation discusses the relationship between geodesic equations and the metric of a 2D manifold. It is possible to generate geodesic curves without a metric, but restoring a metric from these curves is a complex problem. It involves solving partial differential equations and may not always result in a suitable or unique solution. Additionally, determining the connection coefficients and torsion is necessary for finding the metric. It is also mentioned that defining geodesics on a subset of a manifold does not necessarily imply no torsion and may not always lead to a correct metric.
  • #1
VladZH
56
1
Let we have a 2D manifold. We choose a coordinate system where we can construct all geodesics through any point. Is it enough to derive a metric from geodesic equation? Or do we need to define something else for the manifold?
 
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  • #2
Geodesic curves are generated by connection; you can have a connection but do not have metric. Restoring metric compatible with symmetric connection is not a simple problem.
 
  • #3
zwierz said:
Geodesic curves are generated by connection; you can have a connection but do not have metric. Restoring metric compatible with symmetric connection is not a simple problem.
Thanks for reply! Could you tell me what is the complexity? As I see I need to solve partial differential equations. That's it?
 
  • #4
Yes, you must solve the PDE to restore metric by known connection; these PDE are not obliged to have a suitable solution as well as they are not obliged to have a unique solution
 
  • #5
There is a question, though. Let we have a curve equation not w.r.t. the affine parameter but a 2D chart. Can I use the geodesic equation with this curve equation to find connection coefficients? If so, will solving further PDE give me a correct metric in this coordinate system?
 
  • #6
VladZH said:
There is a question, though. Let we have a curve equation not w.r.t. the affine parameter but a 2D chart. Can I use the geodesic equation with this curve equation to find connection coefficients? If so, will solving further PDE give me a correct metric in this coordinate system?
In general, no. The geodesic equation does not depend on the anti-symmetric part of the connection coefficients. You can only find the connection coefficients if you also specify the anti-symmetric part (i.e., you need to specify the torsion).
 
  • #7
Orodruin said:
In general, no. The geodesic equation does not depend on the anti-symmetric part of the connection coefficients. You can only find the connection coefficients if you also specify the anti-symmetric part (i.e., you need to specify the torsion).
Can my chosen curve/curves family give me information about torsion? Should it have second derivative to have a torsion?
 
  • #8
Is there really no answer?
 
  • #10

1. What is a metric tensor derived from a geodesic?

A metric tensor derived from a geodesic is a mathematical object that describes the intrinsic curvature of a space. It is derived from the geodesic equation, which is a fundamental equation in the study of curved spaces.

2. How is a metric tensor derived from a geodesic used in physics?

In physics, a metric tensor derived from a geodesic is used to describe the geometry of spacetime in general relativity. It is also used in other areas of physics, such as in the study of fluid dynamics and quantum field theory.

3. What is the difference between a metric tensor and a metric tensor derived from a geodesic?

A metric tensor is a mathematical object that describes the distance between two points in a space. A metric tensor derived from a geodesic is a specific type of metric tensor that is derived from the geodesic equation. This means that it takes into account the curvature of the space, rather than just the distance between points.

4. How is a metric tensor derived from a geodesic calculated?

A metric tensor derived from a geodesic is calculated using the geodesic equation, which takes into account the curvature of the space. It involves solving a set of differential equations, which can be quite complex depending on the specific space being studied.

5. What are some real-world applications of a metric tensor derived from a geodesic?

A metric tensor derived from a geodesic has many real-world applications, including in GPS navigation systems, which use general relativity to accurately measure distances. It is also used in the study of cosmology, where it helps to describe the large-scale structure of the universe.

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