Null geodesics and null curves

Click For Summary

Discussion Overview

The discussion centers on the distinction between null geodesics and null curves, exploring both qualitative and quantitative aspects. Participants seek to clarify the definitions and implications of these concepts in the context of physics.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant asks for a clear distinction between null geodesics and null curves, indicating a desire for both qualitative and quantitative explanations.
  • Another participant states that null geodesics are parametrized such that the tangent vector is parallel transported along the path, while this property does not necessarily hold for all null curves.
  • A third participant provides an example of a circular light-speed path in polar coordinates, suggesting that this path is a null curve but not a geodesic, noting that light would not follow this path in a vacuum.
  • A subsequent reply expresses gratitude towards the previous contributors, indicating engagement with the discussion.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the definitions and implications of null geodesics versus null curves, with multiple viewpoints and examples presented.

Contextual Notes

The discussion includes assumptions about the properties of paths in spacetime and the conditions under which light travels, which may not be fully articulated or resolved.

blueelectrons
Messages
2
Reaction score
0
What is the exact difference between null geodesics and null curves? Please explain both qualitatively and quantitatively.
 
Physics news on Phys.org
Null geodesics are parametrised such that the tangent vector is parallel transported along it. This is not necessarily the case for any null curve.
 
  • Like
Likes   Reactions: blueelectrons
Consider the path, in polar coordinates: θ = ct/R

A circular light speed path of radius R. This is null path that is not geodesic. Light would not take such a path in vaccuo.
 
  • Like
Likes   Reactions: VEReade, blueelectrons and bcrowell
ok..thanks Orodruin and PAllen.
 

Similar threads

Undergrad Affine parameter and non-geodesic null curves
  • · Replies 1 ·
Replies
1
Views
1K
Graduate Minimal property of Spacelike geodesics in GR/curved spacetime?
  • · Replies 76 ·
3
Replies
76
Views
4K
Undergrad Future null infinity confusion
  • · Replies 30 ·
2
Replies
30
Views
8K
Graduate Computing Null Geodesics in Schwarzschild Geometry
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Detecting Gravitational Waves w/ Interferometers: Explained
  • · Replies 11 ·
Replies
11
Views
2K
Graduate Tensors in null basis
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Notion of parallel worldlines in curved geometry
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Curvature with different connections on the two-sphere
  • · Replies 15 ·
Replies
15
Views
2K
Undergrad About the meaning of "expanding universe"
  • · Replies 16 ·
Replies
16
Views
2K
Undergrad Connection & Affine Geodesics: Q&A
  • · Replies 7 ·
Replies
7
Views
2K