A simple example is that the charge density can be a source term
the charge interaction term is $- ie j_\mu A^\mu$
This can be interpreted either as a given charge density, or you can express it as being another field, such as the fermionic charge $\bar \psi \gamma_\mu \psi$
In calculating a Greens function, going from k-space to realspace, I encountered a sum, but how would I go about evaluating the sum? It seems pretty standard www5b.wolframalpha.com/Calculate/MSP/…
In many cases an animation would make an answer much clearer.
Here on Physics Meta there was already the question if it is possible to add animations to answers.
A comment suggests using animated GIF files. The (as of now) only answer is saying that the Stack Exchange team does not like adding ad...
BTW, I really loved the character of Johan (more than that of Kenzo). And second best character (at least for me, tough to judge) is that of Inspector Lunge.
