I am going through the introductory chapter's of Schwinger's Source theory. He writes,
It [Source Theory] is a phenomenological theory, designed to describe the observed particles. No speculations about the inner structure of the particles are introduced. No abstract definition of particle is devised. The theory is thereby firmly grounded in space-time, where the experimenter manipulates his tools, but the question of ultimate limitation to microscopic space-time description is left open, with the decision reserved to experiments. Correspondingly, no Operator-fields are used.
Now in this regard, I would want to know how operator fields answer the question of ultimate limitations to microscopic space-time (If they are related to each other)?
EDIT 1 : It just struck me that the limitation could be due to canonical commutation between field operators and their conjugates. However, I don't see how to formalize a restriction using this commutation.