I have a very naive confusion regarding the propagators of QFT. I have come across the terms:
(i) Retarded propagator,
(ii) Advanced propagator,
(iii) Feynman propagator ...
I can comprehend the derivation of these different propagators and how they come to be. However I don't understand what do they mean? What kind of retardation is there? In electromagnetism with special relativity, the retarded potential implies, for a moving source charge, the potential a test charge faces is not what the source charge create from its current position. Rather, what the test charge faces is the potential due the source charge's position at some time ago. So the word. 'retarded potential' makes perfect sense to me in the context of relativistic electromagnetism. I can't say the same for the case of above propagators.
Is there even a meaning to all these nomenclature? I am stuck at this point in QFT for a long time. It would be really nice if anyone can help me out.
