Calculate Eigenvalues of Electromagnetic & Stress-Energy Tensors

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Discussion Overview

The discussion revolves around calculating the eigenvalues of the electromagnetic tensor ##F_{ab}## and the stress-energy tensor ##T_{ab}##, exploring both the mathematical approach and the physical implications of these eigenvalues. The scope includes theoretical considerations and mathematical reasoning related to tensor properties.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant suggests calculating the eigenvalues of ##F_{ab}## and ##T_{ab}## without using the characteristic polynomial, questioning their physical meaning.
  • Another participant notes that the eigenvalues of a real antisymmetric matrix are imaginary and proposes computing the eigenvalues of its square as a potential method.
  • A different participant challenges the notion of eigenvalues for the tensors, stating that ##T_{\mu\nu}## and ##F_{\mu\nu}## are (0,2) tensors and thus do not have eigenvalues in the traditional sense, although they acknowledge the possibility of manipulating indices using the metric.
  • One participant shares links to external resources that may provide additional context or related information on the classification of electromagnetic fields.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of eigenvalues to the tensors in question, with some arguing for their relevance and others contesting the definition of eigenvalues in this context. The discussion remains unresolved regarding the proper approach to calculating eigenvalues and their interpretation.

Contextual Notes

The discussion highlights the dependence on definitions of eigenvalues and the implications of tensor types, as well as the potential limitations in the mathematical treatment of these tensors.

ergospherical
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How can we (as nicely as possible... i.e. not via characteristic polynomial) calculate the eigenvalues of ##F_{ab} = \partial_a A_b -\partial_b A_a## and ##T_{ab} = F_{ac} {F_b}^c- (1/4) \eta_{ab} F^2 ## and what is their physical meaning?
 
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I mean, first of all you would have to define what you mean by "eigenvalues". The entire concept of an eigenvalue is that you have an operator from a vector space to itself. As such, neither ##T_{\mu\nu}## or ##F_{\mu\nu}## have eigenvalues because they are (0,2) tensors. You can, of course, raise and lower an index using the metric if you have one, but then you no longer have a symmetric or anti-symmetric matrix.
 
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