Obtaining the Metric in a Boosted Observer Frame?

  • Context: Graduate 
  • Thread starter Thread starter Mentz114
  • Start date Start date
  • Tags Tags
    Basis Frame
Click For Summary
SUMMARY

This discussion focuses on obtaining the metric in the frame of a boosted observer within a specific spacetime characterized by coframe and frame basis vectors. The user presents their calculations for the new frame basis after applying a boost in the φ direction, resulting in transformed basis vectors. They express uncertainty regarding the correctness of their derived coframe basis and seek validation and pointers for potential errors, referencing Lee's "Riemannian Manifolds: An Introduction to Curvature" for foundational concepts.

PREREQUISITES
  • Understanding of coframe and frame basis vectors in differential geometry
  • Familiarity with Lorentz transformations and boosts in special relativity
  • Knowledge of Riemannian geometry concepts as outlined in Lee's "Riemannian Manifolds: An Introduction to Curvature"
  • Proficiency in tensor calculus and differential forms
NEXT STEPS
  • Review the derivation of Lorentz transformations and their application to frame transformations
  • Study the properties of dual coframes and their relationship with local frames in Riemannian geometry
  • Examine examples of boosted observer metrics in relativistic physics
  • Explore advanced topics in differential geometry, focusing on curvature and its implications in physics
USEFUL FOR

This discussion is beneficial for physicists, mathematicians, and students specializing in general relativity, differential geometry, and those interested in the mathematical foundations of spacetime metrics.

Mentz114
Messages
5,429
Reaction score
292
I'm trying to get a metric in the frame of a boosted observer. The spacetime in question has coframe and frame basis vectors

[tex] \begin{align*}<br /> \vec{\sigma}^0 = \frac{-1}{\sqrt{F}}dt\ \ \ \ & \vec{e}_0 = -\sqrt{F}\partial_t \\<br /> \vec{\sigma}^1 = \sqrt{F}dz\ \ \ \ & \vec{e}_1 = \frac{1}{\sqrt{F}}\partial_z \\<br /> \vec{\sigma}^2 = \sqrt{F}dr\ \ \ \ & \vec{e}_2 = \frac{1}{\sqrt{F}}\partial_r \\<br /> \vec{\sigma}^3 = r\sqrt{F}d\phi\ \ \ \ & \vec{e}_3 = \frac{1}{r\sqrt{F}}\partial_\phi <br /> \end{align*}[/tex]

Boosting the coordinate frame basis by [itex]\beta[/itex] in the [itex]\phi[/itex] direction gives the new frame basis

[tex] \begin{align*}<br /> \vec{f}_0 &= -\gamma\sqrt{F}\partial_t + \gamma\beta \frac{1}{r\sqrt{F}}\partial_\phi \\<br /> \vec{f}_1 &= \frac{1}{\sqrt{F}}\partial_z \\<br /> \vec{f}_2 &= \frac{1}{\sqrt{F}}\partial_r \\<br /> \vec{f}_3 &= \gamma\frac{1}{r\sqrt{F}}\partial_\phi + \gamma\beta \sqrt{F}\partial_t <br /> \end{align*}[/tex]

Now, my problem is reading off the new coframe basis [itex]s[/itex]. My attempt is below, but I'm only 50% confident it's right.

[tex] \begin{align*}<br /> {\vec{s}}^0 &= (\gamma\sqrt{F})^{-1}dt+(\gamma\beta)^{-1}r\sqrt{F}d\phi \\<br /> {\vec{s}}^1 &= \sqrt{F}dz \\<br /> {\vec{s}}^2 &= \sqrt{F}dr \\<br /> {\vec{s}}^3 &= \gamma^{-1}r\sqrt{F}d\phi + (\gamma\beta)^{-1}\sqrt{F}dt<br /> \end{align*}[/tex]

The metric that arises from this is sort of plausible. I'd appreciate any pointers, particularly to any errors.
 
Physics news on Phys.org
From Lee's book "Riemanian Manifolds : An Introduction to Curvature" ( page 30)

Let (E1, . . . , En) be any local frame for TM, that is, n smooth vector fields defined on some open set U such that (E1|p, . . . , En|p) form a basis for TpM at each point p ∈ U. Associated with such a frame is the dual coframe, which we denote (ϕ1, . . . , ϕn); these are smooth 1-forms satisfying ϕi(Ej) = δij.

Couldn't be simpler really.
 

Similar threads

  • · Replies 15 ·
Replies
15
Views
1K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 6 ·
Replies
6
Views
1K
  • · Replies 23 ·
Replies
23
Views
3K
  • · Replies 0 ·
Replies
0
Views
3K
  • · Replies 5 ·
Replies
5
Views
1K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 38 ·
2
Replies
38
Views
4K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 12 ·
Replies
12
Views
3K