Electromagnetic dual tensor. General Relativity

In summary, the equations Eq 1 and Eq 2 are equivalent. The first term of Eq 1 reads: F sub alpha beta comma gamma. The book says that Eq 1 and Eq 2 are equivalent. I am just showing Eq 2 because I know that the book's notation is confusing. Eq 2 means the gradient of the tensor F. Does your equation dw mean the same? Because it seems to me as the differential, and w being a scalar...
  • #1
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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  • #2
Here, I type-set them for you...
[tex] F_{\alpha\beta,\gamma} + F_{\beta\gamma,\alpha} + F_{\gamma \alpha,\beta} = 0[/tex]
[tex] \mathbf{dF} = 0[/tex]
[tex]\mathbf{\nabla}\bullet {}^\star \mathbf{F}=0[/tex]
[tex][F_{\alpha\beta}] = \left[ \begin{array}{c c c c}0 & -E_x & -E_y & -E_z\\
E_x & 0 & B_z &-B_y\\
E_y & -B_z & 0 & B_x\\
E_z & B_y & -B_x 0\end{array}\right][/tex]
[tex][{}^\star F_{\alpha\beta}] = \left[ \begin{array}{c c c c}0 & B_x & B_y & B_z\\
-B_x & 0 & E_z &-E_y\\
-B_y & -E_z & 0 & E_x\\
-B_z & E_y & -E_x 0\end{array}\right][/tex]
 
  • #3
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.

[tex] \mathbf{d} \omega = \mathbf{dx}^\mu \wedge \partial_\mu \omega[/tex]

To translate the matrix format to differential forms, you contract the matrix with the bivector basis:
[tex]\mathbf{F} =\frac{1}{2} F_{\mu\nu} \mathbf{dx}^\mu\wedge \mathbf{dx}^\nu[/tex]
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. [itex] \mathbf{dx}^1\wedge \mathbf{dx}^2=- \mathbf{dx}^2 \wedge \mathbf{dx}^1[/itex]

(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.
 
  • #4
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.
 
  • #5
jambaugh said:
[tex] \mathbf{d} \omega = \mathbf{dx}^\mu \wedge \partial_\mu \omega[/tex]

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.
 
Last edited:

1. What is an electromagnetic dual tensor?

The electromagnetic dual tensor is a mathematical object used in the study of electromagnetism. It is a combination of the electric and magnetic fields, represented by a 4x4 matrix, that allows for a concise and elegant description of electromagnetic phenomena.

2. How is the electromagnetic dual tensor related to general relativity?

In general relativity, the electromagnetic dual tensor is used to describe the curvature of spacetime caused by electromagnetic fields. This is known as the electromagnetic stress-energy tensor, and it is an important component in the Einstein field equations that govern the behavior of gravity.

3. What is the significance of the electromagnetic dual tensor in physics?

The electromagnetic dual tensor is a fundamental concept in theoretical physics, as it allows for a unified understanding of electromagnetism and gravity. It is also used in the development of theories such as quantum electrodynamics and string theory.

4. How is the electromagnetic dual tensor calculated?

The electromagnetic dual tensor can be calculated using Maxwell's equations, which describe the behavior of electromagnetic fields. It involves taking the curl of the electric and magnetic fields and combining them in a specific way to form the 4x4 matrix.

5. What are some practical applications of the electromagnetic dual tensor?

The electromagnetic dual tensor has numerous applications in modern technology, such as in the design of antennas, electromagnetic sensors, and satellite communication systems. It is also used in medical imaging techniques such as magnetic resonance imaging (MRI).

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