ABSTRACT
Bruin the First had a long career behind him; he could build a den and root up trees; hence, with certain
allowances, he could pass for an expert engineer. His greatest merit, however, was his ardent desire to figure in the annals
of History. For this reason he preferred the glories of bloodshed to everything else world. And so, whatever he spoke of, be it commerce, industry or science, he always
ended the same: “Blood, sirs, blood, that’s what we need”. M.E. Saltykov Shchedrin, “Bears in Government”
Interest in a free-field theory is by no means purely academic. Before and after the particle collision in the process of scattering (known as the key experiment in the microworld) the distance between these particles is so great that their interaction is practically zero. Because of this, we can consider the particles at the initial and final states to be free. To describe such a physical situation, an adequate mathematical operation-the representation of interaction-may be used for going from equations of interacting fields to the free-field equations. Of course, we have to do with a certain idealization; there is no possibility to exclude interactions all together, while interactions between the scattered particles are excluded. In other words, exact equations for particles at the initial and final states have to include the terms determining the interactions with the environment.
