I'm going crazy (Electromagnetic Energy-Momentum Tensor)

In summary, the conversation discusses a problem with a solution provided in a link. The person is struggling to understand how the antisymmetry of a certain term allows for rewriting a complicated expression in a simpler form. The solution involves relabeling dummy indices to obtain the desired result.
  • #1
LineIntegral
9
0

Homework Statement



The problem is conveniently located here:

http://www.dur.ac.uk/resources/cpt/graduate/lectures/mscps.pdf

Problem no. 31. There's even a solution, here:

http://www.dur.ac.uk/resources/cpt/graduate/lectures/grsolns.pdf

However, I don't understand the solution. How does the antisymmetry of [tex]F^{\rho\lambda}[/tex] allow us to rewrite [tex]\nabla_\rho F_{\sigma\lambda} - \frac{1}{2} \nabla_\sigma F_{\rho\lambda}[/tex] as [tex]\frac{1}{2}\left ( \nabla_\rho F_{\sigma\lambda} - \nabla_\lambda F_{\sigma\rho} - \nabla_\sigma F_{\rho\lambda} \right )[/tex] ? I just don't see it. This implies that [tex]\nabla_\rho F_{\sigma\lambda} = -\nabla_\lambda F_{\sigma\rho}[/tex], which doesn't seem right...

Homework Equations



See above.


The Attempt at a Solution



See above.

Any help will be much appreciated!
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
The point is that you have

[tex]F^{\rho\lambda} \nabla_\rho F_{\sigma\lambda} = \frac{1}{2} (F^{\rho\lambda}-F^{\lambda\rho}) \nabla_\rho F_{\sigma\lambda}.[/tex]

After a relabeling of dummy indices, you find the claimed result.
 
  • #3
Thanks! Now it finally makes sense... :)
 

1. What is the electromagnetic energy-momentum tensor?

The electromagnetic energy-momentum tensor is a mathematical quantity used in the field of electromagnetism to describe the distribution of energy and momentum in an electromagnetic field. It is a 4x4 matrix that contains information about the electric and magnetic fields, as well as their interactions with matter.

2. How is the electromagnetic energy-momentum tensor derived?

The electromagnetic energy-momentum tensor is derived from the electromagnetic stress-energy tensor, which is a combination of the electromagnetic field tensor and the energy-momentum tensor. It is based on the principles of special relativity and Maxwell's equations.

3. What is the significance of the electromagnetic energy-momentum tensor?

The electromagnetic energy-momentum tensor is significant because it allows us to understand and predict the behavior of electromagnetic fields, such as light and radio waves. It also plays a crucial role in the theory of general relativity, as it is used to describe the curvature of spacetime caused by electromagnetic fields.

4. How is the electromagnetic energy-momentum tensor used in practical applications?

The electromagnetic energy-momentum tensor is used in a variety of practical applications, such as in the design and optimization of antennas and other electromagnetic devices. It is also important in the study of electromagnetic radiation and its effects on matter, as well as in the development of technologies such as wireless communication and medical imaging.

5. Are there any limitations to the use of the electromagnetic energy-momentum tensor?

Like any mathematical model, the electromagnetic energy-momentum tensor has its limitations. It is based on classical electromagnetism and does not take into account quantum effects, which are important at very small scales. Additionally, it assumes that all matter is continuous, whereas at the atomic level, matter is composed of discrete particles. Therefore, the electromagnetic energy-momentum tensor is not applicable in all situations and must be used with caution.

Similar threads

  • Advanced Physics Homework Help
Replies
30
Views
5K
  • Advanced Physics Homework Help
Replies
1
Views
329
  • Advanced Physics Homework Help
Replies
11
Views
2K
Replies
5
Views
2K
  • Advanced Physics Homework Help
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
16
Views
2K
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Special and General Relativity
Replies
4
Views
3K
  • Advanced Physics Homework Help
Replies
1
Views
2K
Replies
6
Views
2K
Back
Top