Antisymmetrization leads to an identically vanishing tensor

  • Context: Graduate 
  • Thread starter Thread starter jason12345
  • Start date Start date
  • Tags Tags
    Tensor
Click For Summary

Discussion Overview

The discussion revolves around the concept of antisymmetrization of tensors, specifically addressing why antisymmetrizing fifth- or higher-rank tensors results in an identically vanishing tensor. Participants seek clarification on this concept as presented in Anderson's Principles of Relativity Physics.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the reasoning behind the statement from Anderson's text regarding antisymmetrization leading to a vanishing tensor.
  • Another participant suggests that antisymmetrization of a tensor with repeated indices results in zero, as the antisymmetric property requires that elements with identical indices must cancel out.
  • Further clarification is provided about the structure of the tensor and the necessity for indices to be distinct when antisymmetrizing.
  • There is a discussion about the labeling of indices and the implications of using different symbols for the same tensor elements, which raises questions about the clarity of the explanation.
  • A participant expresses that while they understand the explanation, they find the reasoning not immediately obvious, particularly in the context of Anderson's broader definitions of tensors.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the antisymmetrization process, with some agreeing on the outcome while others find the explanation lacking in clarity. The discussion remains unresolved regarding the intuitiveness of the concept as presented in the text.

Contextual Notes

Participants note that the definitions and context provided by Anderson may not fully clarify the reasoning behind the antisymmetrization leading to a vanishing tensor, indicating potential limitations in the explanation.

jason12345
Messages
108
Reaction score
0
This comes from Andersons's Principles of Relativity Physics:

"Of course, for fifth- or higher-rank tensors antisymmetrization leads to an
identically vanishing tensor"

But I don't understand why, even if it's "of course". So can someone show me why?
 
Physics news on Phys.org
Hi jason12345! :smile:

Because any tensor Aabcde has elements which look like Axyztx (or worse), and if A is antisymmetric, then this must be zero. :wink:
 


tiny-tim said:
Hi jason12345! :smile:

Because any tensor Aabcde has elements which look like Axyztx (or worse), and if A is antisymmetric, then this must be zero. :wink:

Antisymmetrising Aabcde means writing it as 1/5!(Aabcde + ... - Abacde -.. ) so that the indices abcde are merely permutated, whereas you have Axyztx which has indices x repeated. Why did you change the labelling from abcde to xyz and then t?

Thanks for your interest.
 
Because the only candidates for the indices for the elements of the matrix are x y z and t (or 1 2 3 and 4, or whatever the four basis elements are) …

each element of the matrix has to have each of a b c d and e equal to x y z or t. :smile:
 


tiny-tim said:
Because the only candidates for the indices for the elements of the matrix are x y z and t (or 1 2 3 and 4, or whatever the four basis elements are) …

each element of the matrix has to have each of a b c d and e equal to x y z or t. :smile:

Thanks, I understand what you're saying now :), although I still say it isn't obvious since Anderson was defining Tensors as general geometrical objects upto this point, it seems, rather than applying them to the space-time manifold.
 

Similar threads

  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
9K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 10 ·
Replies
10
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 0 ·
Replies
0
Views
993
  • · Replies 4 ·
Replies
4
Views
3K