Determining Geometry of Line Element: A General Method?

Click For Summary

Discussion Overview

The discussion centers around the question of how to determine the geometry described by a given line element in the context of differential geometry and general relativity. Participants explore methods for analyzing arbitrary line elements and the implications for understanding the underlying geometric structure of spacetime.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the line element itself encapsulates the geometry, questioning what additional information is sought beyond the metric.
  • Others propose that calculating the Riemann curvature tensor can provide insights into the geometry described by a line element.
  • One participant highlights the challenge of determining whether different line elements, such as the Schwarzschild and Eddington-Finkelstein line elements, describe the same spacetime, noting the difficulty in finding a coordinate transformation between them.
  • It is mentioned that if a continuous differentiable transformation exists that relates the metric tensor components of two line elements, then they may represent different coordinate systems for the same geometry.
  • Another point raised is that the transformation must be invertible in the regions covered by both coordinate systems for the equivalence to hold.

Areas of Agreement / Disagreement

Participants express differing views on the methods for determining the geometry from a line element, with no consensus on a general method. The discussion remains unresolved regarding the best approach to analyze arbitrary line elements and their geometric implications.

Contextual Notes

Limitations include the dependence on the existence of coordinate transformations and the conditions under which they apply. The discussion does not resolve the complexities involved in determining the geometry from line elements.

steve1763
Messages
13
Reaction score
0
TL;DR
Given an arbitrary line element, how does one calculate the geometry of the space that it describes?
Is there a general method to determine what geometry some line element is describing? I realize that you can tell whether a space is flat or not (by diagonalising the matrix, rescaling etc), but given some arbitrary line element, how does one determine the shape of the space?

Thanks
 
Physics news on Phys.org
I am not sure what you mean. The line element is what describes the shape. What information are you looking for that is not already captured in the metric?
 
steve1763 said:
Summary:: Given an arbitrary line element, how does one calculate the geometry of the space that it describes?

Is there a general method to determine what geometry some line element is describing? I realize that you can tell whether a space is flat or not (by diagonalising the matrix, rescaling etc), but given some arbitrary line element, how does one determine the shape of the space?

Thanks
You can also compute the Riemann curvature tensor.
 
steve1763 said:
Is there a general method to determine what geometry some line element is describing?
If you mean that, given the Schwarzschild line element and the Eddington-Finkelstein line element, how do you know that they describe the same spacetime, the answer is "with difficulty". You really need to find a transform from one set of coordinates to the other and I don't think there's a recipe for that.
 
  • Like
Likes   Reactions: vanhees71 and cianfa72
Ibix said:
If you mean that, given the Schwarzschild line element and the Eddington-Finkelstein line element, how do you know that they describe the same spacetime, the answer is "with difficulty". You really need to find a transform from one set of coordinates to the other and I don't think there's a recipe for that.
Yes, I believe the main point is the following: if you can find (actually if it does exist !) a continuous differentiable transformation such that the metric tensor components transform into the others, then the two are actually different coordinate systems for the same underlying geometry.
 
  • Like
Likes   Reactions: vanhees71 and Ibix
cianfa72 said:
if you can find (actually if it does exist !) a continuous differentiable transformation such that the metric tensor components transform into the others
The transformation must be invertible in the regions both coordinate systems cover, as well.
 
  • Like
Likes   Reactions: vanhees71 and cianfa72

Similar threads

  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 17 ·
Replies
17
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 11 ·
Replies
11
Views
1K
  • · Replies 62 ·
3
Replies
62
Views
7K
  • · Replies 30 ·
2
Replies
30
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 95 ·
4
Replies
95
Views
8K
  • · Replies 35 ·
2
Replies
35
Views
5K