Electromagnetic dual tensor. General Relativity

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SUMMARY

The discussion focuses on demonstrating the equivalency between Maxwell's equations represented in different forms, specifically Eq (1) and Eq (3), using the electromagnetic tensor F and its dual. The equations discussed include the gradient of F, represented as Eq (2), and the matrix representations of the electromagnetic tensor and its dual. The participants emphasize the importance of understanding tensor notation and the dimensionality of different tensor ranks, particularly in the context of General Relativity as outlined in the book "Gravitation" by Misner, Thorne, and Wheeler.

PREREQUISITES
  • Understanding of Maxwell's equations in the context of electromagnetism.
  • Familiarity with tensor notation and operations, specifically in General Relativity.
  • Knowledge of differential forms and their applications in physics.
  • Basic understanding of matrix representations of tensors.
NEXT STEPS
  • Study the properties of the electromagnetic tensor F and its dual, focusing on their mathematical representations.
  • Learn about the Hodge dual operator and its role in transforming tensor equations.
  • Explore the concept of rank in tensors and how it affects the dimensionality of tensor spaces.
  • Investigate the relationship between differential forms and tensor calculus in the context of General Relativity.
USEFUL FOR

This discussion is beneficial for physics students, particularly those studying General Relativity, as well as researchers and educators looking to deepen their understanding of electromagnetic theory and tensor analysis.

TheSource007
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Homework Statement


I attach a word document with the equations because I don't know how to write them on the post.
My question reads: Show that Maxwell's equations Eq (1) is equivalent to Eq (3).

Homework Equations


The first term of Eq 1 reads: F sub alpha beta comma gamma. That means partial of F sub alpha beta with respect to x super gamma.
The book says that Eq 1 and Eq 2 are equivalents. I am just showing Eq 2 because I know that the book's notation is confusing.
Eq 2 means the gradient of F, which is the EM tensor.
Eq (4) is the components electromagnetic tensor.
And I have calculated the components of the dual tensor *F which are Eq (5)

The Attempt at a Solution


I have written Eq (3) in matrix notation, but I don't think it resembles Eq (1) or Eq (2). Also, I know that Eq 2 is a 3rd rank tensor due to the gradient.
I have no idea how to show the equivalency between 1 and 3.
The book I am using is Mister, Thorne, Wheeler Gravitation, but this is a undergraduate level course in general relativity, and I am very new at this tensor stuff, so please be gently.

Thank you for your help
 

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Here, I type-set them for you...
F_{\alpha\beta,\gamma} + F_{\beta\gamma,\alpha} + F_{\gamma \alpha,\beta} = 0
\mathbf{dF} = 0
\mathbf{\nabla}\bullet {}^\star \mathbf{F}=0
[F_{\alpha\beta}] = \left[ \begin{array}{c c c c}0 &amp; -E_x &amp; -E_y &amp; -E_z\\<br /> E_x &amp; 0 &amp; B_z &amp;-B_y\\<br /> E_y &amp; -B_z &amp; 0 &amp; B_x\\<br /> E_z &amp; B_y &amp; -B_x 0\end{array}\right]
[{}^\star F_{\alpha\beta}] = \left[ \begin{array}{c c c c}0 &amp; B_x &amp; B_y &amp; B_z\\<br /> -B_x &amp; 0 &amp; E_z &amp;-E_y\\<br /> -B_y &amp; -E_z &amp; 0 &amp; E_x\\<br /> -B_z &amp; E_y &amp; -E_x 0\end{array}\right]
 
Your post didn't complete the sentence so I'm not clear on what is your question. But if you want to show equivalence of the first three equations, you have to expand the notation.

\mathbf{d} \omega = \mathbf{dx}^\mu \wedge \partial_\mu \omega

To translate the matrix format to differential forms, you contract the matrix with the bivector basis:
\mathbf{F} =\frac{1}{2} F_{\mu\nu} \mathbf{dx}^\mu\wedge \mathbf{dx}^\nu
The factor of 1/2 is not vital since these are homogenous equations but are there to account for the double counting of e.g. \mathbf{dx}^1\wedge \mathbf{dx}^2=- \mathbf{dx}^2 \wedge \mathbf{dx}^1

(to properly sum you should be summing, not over each index, but over the set of unique anti-symmetric pairs... or throw in the factor of 1/2 to get the same thing.)

You now need to parse through the definitions and see what results.
 
A second observation. Note the first is a rank 3 tensor equation (three free indices).
The second is a rank-3 tensor equation (the outer differential of a bi-vector is a tri-vector), and the last is a vector equation (the divergence of a 2-tensor is a 1 tensor).

Given each case will be a totally anti-symmetrized tensor, one can count the dimensions of these tensor spaces. Given totally antisymmetized indices in 4 dimensions you have 4 choose r ways to select distinct indices so the dimensions are:
rank 0 (scalar) dim=1
rank 1 (vector) dim=4
rank 2 (bi-vector) dim=6
rank 3 ("tri-vector") dim = 4
rank 4 (The Levi-Civita tensor) dim = 1

The hodge dual swaps these equal dimension tensor spaces.
So you should find each of your equations is a set of 4 equations, either 4-vector or "tri-vector"=rank 3 antisymmetric tensor.
 
jambaugh said:
\mathbf{d} \omega = \mathbf{dx}^\mu \wedge \partial_\mu \omega

I updated my post.
Eq 2 means the gradient of the tensor F.
Does your equation dw means the same? Because it seems to me as the differential, and w being a scalar...
As I said (in my update) I am very new at this.
Thank you.
 
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