Talk:Electromagnetic stress–energy tensor

message: This article is non-standard since it uses CGS instead of SI and an arrow to symbolize a vector instead of boldface (it's not even the right arrow). 88.154.158.95 13:10, 25 November 2006 (UTC)
replies: text: SI units are now included as well as CGS units. JRSpriggs (talk) 06:00, 11 April 2008 (UTC)
thread_title:  CGS or SI units 

message: The page name should reflect the fact that the article is limited to the energy-momentum tensor for electromagnetic fields.  Saligron 04:54, 29 January 2007 (UTC)
replies: text: I moved this article from "Energy momentum tensor" to "Electromagnetic stress-energy tensor" which is a more accurate description of the contents. I hope that this is acceptable to you. JRSpriggs 09:34, 29 January 2007 (UTC)
replies: text:  The name fits much better.  Thanks.  Saligron 10:43, 29 January 2007 (UTC)

text: I think you should re-redirect "Energy momentum tensor" to "Stress-energy tensor". Hwasungmars 19:53, 30 May 2007 (UTC)
replies: text: Good idea. Done. JRSpriggs 08:31, 31 May 2007 (UTC)
thread_title:  Rename 

message: I am not sure at present what is the correct formula in each system of units. However, I am sure that some of these formulas are wrong. There should be a factor of 1/4 in the first formula which is missing, for example. JRSpriggs 10:13, 20 April 2007 (UTC)
replies: text: Well, c=1 unit is of the so-called "geometric units" or "standard relativistic units" which has no relation with Planck units at all. You might mix them up. Nevertheless, the formula as what I keyed in is correct for c=1 unit convention, and \epsilon_o=\frac{1}{\mu_o} holds, which can further simplify the tensor. All of these come from James Hartle's General Relativity textbook. --KasugaHuang 14:45, 24 April 2007 (UTC)
replies: text: As for the first formula, if you mean this: T^{\alpha\beta} = \epsilon_o [ -F^{\alpha \gamma}F_{\gamma}^{\beta} + g^{\alpha\beta}F_{\gamma\delta}F^{\gamma\delta}], this is not what I keyed in, and further confirmation may be required. :) --KasugaHuang 14:52, 24 April 2007 (UTC)

text: I tried to fix the problems that were apparent to me, but they may still have errors. JRSpriggs 04:09, 1 May 2007 (UTC)
thread_title:  The relativistic formula for the tensor 

message: I think there is not only a problem with the common prefactor (which may be different in different unit systems), but there is also a problem about the definition of the common sign for the stress-energy tensor.
Apart from the sign and prefactor convention problems, there might be a sign confusion: the first and second summand in the em. stress-energy tensor might have same or opposite sign depending on how the contractions are performed. Since F is antisymmetric, one has to specify for the form with upper and lower indices, which one is first and which is second. -- 17:16, 24 March 2008 
:I calculated the whole thing. I do think there should be a minus sign before everything. This formula is for (-1, 1, 1, 1) metric tensor but not for (1, -1, -1, -1) one. --128.122.52.204 (talk) 21:42, 22 September 2008 (UTC)
replies: text: The sign convenion for the metric is opposite to the one used in the definition of the E-M field-tensor electromagnetic tensor Nielswalet (talk) 11:28, 13 December 2012 (UTC)

text: Also disagrees with Stress–energy tensor Nielswalet (talk) 15:29, 13 December 2012 (UTC)
thread_title:  Sign conventions and sign problems 

message: I believe in this article there is a problem in the explicit matrix form of the electromagnetic stress-energy tensor. The Pointing vectors Sx, Sy, Sz in the matrix should be divided by the speed of light, c[m/s]. This is because all elements of the matrix should have the same dimension of [J/m3]. Bspasov (talk) 19:27, 10 April 2008 (UTC)
replies: text: Actually, the components of a tensor should not all have the same units. In SI units, time is measured in seconds and distance is measured in meters. Thus the position 4-vector has units of [seconds, meters, meters, meters]. More generally, a factor of (seconds/meter)^(# of contravariant time indices − # of covariant time indices) must be multiplied by the units of the purely spatial components to get the units of components involving time. JRSpriggs (talk) 06:00, 11 April 2008 (UTC)
replies: text: This is an old conversation, but for the record, I disagree with JRSpriggs here. In the textbooks I've seen, all four components of a four-vector always have the same units. For example, the "position 4-vector" is defined as (ct,x,y,z).  --Steve (talk) 00:15, 18 January 2011 (UTC)
thread_title:  Units of the components in the explicit matrix form 

message: Who derived this tensor equation? Maxwell was of course a while ago. But who came up with this portrayal? Oh, just found it in The Foundations of the Genreal Theory of Relativity by Einstein.
Bruce rout (talk) 22:45, 17 September 2008 (UTC)
thread_title:  Source please. 

message: The two terms of the tensor should have opposite sign. Look at Wald's book, equation 4.3.14  —Preceding unsigned comment added by 147.52.186.56 (talk) 14:31, 17 January 2011 (UTC)
thread_title:  The tensor is wrong 

message: The definition of σ[sub i j] must be wrong. There is a kronecker delta indexed by i and j, but it multiplies a term that has no subscripts at all.  — Preceding unsigned comment added by Zfiddler (talk • contribs) 08:58, 14 November 2016 (UTC)
replies: text: The term without index is the absolute value of the electric/ magnetic field field. Biggerj1 (talk) 12:27, 4 September 2018 (UTC)
thread_title:  Definition of sigma must be wrong.