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swampwiz
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I was reading this:
However, which only coincides with his final (correct) equation if the stress-energy tensor T (and hence also R) is traceless, i.e. that the sum of the elements on the main diagonal of the matrix trace are zero), which is true for Maxwell’s electrodynamics.
That's the ticket!Baluncore said:Maybe this will explain it.
https://en.wikipedia.org/wiki/Electromagnetic_tensor#Relationship_with_the_classical_fields
So then it would seem that QED theory has a quandary; no wonder so little progress has been made.vanhees71 said:The reason is scale invariance of the free Maxwell equations. This symmetry is, however, very fragile since it's anomalously broken when quantizing the theory.
Because the symmetry is broken when quantizing?vanhees71 said:What do you mean by "QED theory has a quandary"? I've no clue. The claim that "so little progress has been made" is just ridiculous particularly in the context of QED.
The Maxwell's Electromagnetism equations, also known as the Maxwell's equations, are a set of four equations that describe the behavior of electric and magnetic fields in space. They were developed by James Clerk Maxwell in the 19th century and are considered fundamental laws of electromagnetism.
The Maxwell's Electromagnetism equations are traceless because they are derived from the principle of charge conservation. This means that the equations must hold true regardless of the reference frame, and thus they must be traceless to satisfy this condition.
Being traceless means that the trace, or the sum of the diagonal elements, of the equations' matrices is equal to zero. In other words, the equations do not contain any terms that depend on the reference frame, making them universally applicable.
The Maxwell's Electromagnetism equations describe the behavior of electric and magnetic fields, which are the two components of an electromagnetic wave. These equations show how the fields interact with each other and with charged particles, leading to the propagation of electromagnetic waves.
While the Maxwell's Electromagnetism equations are generally considered traceless, there are some situations where this property may not hold true. For example, in the presence of magnetic monopoles or in certain non-inertial reference frames, the equations may contain trace terms. However, these exceptions are not commonly encountered in most practical applications.