| Summary: | In this essay we discuss epistemological implications of relativistic quantum ?eld theory. The empirical domain of such a theory is formed by phenomena ascribed tosubnuclearparticles, sometimes still calledelementaryparticles. Thislattermoretraditionaldesignationre?ectsthelastingdesireofphysicists to eventually ?nd and isolate irreducible constituents of matter. Going down to the atomic level, electrons appear to play such a role, ˆ whereas the nuclei of atomscanbeconsideredascompoundsystemsofprotonsandneutrons,i. e. of two species of particles. This view makes sense, since the respective number of these two types of constituents essentially identi?es an atomic nucleus. Extracted from a nucleus, however, the 'free'neutron is an unstable particle: it decays spontaneously into a proton, an electron and an anti-neutrino. In the past ?fty years or so basically the bombardment of matter by protons or by electrons in specially devised experiments has revealed a large variety of furthersubnuclearobjects. Successivegenerationsofacceleratorsandre?ned collisiondevicesprovidedhigherandhighercollisionenergies. Alltheses- nuclear objects are termed 'particles'in the physics community, nearly all of these objects are unstable and decay spontaneously into other ones. The - spective lifetimes of the distinct types, however, differ widely, ranging from 3 ?25 relatively long(10 sec) to extremely short(10 sec). Because of this huge disparity in lifetime the notion of a particle deserves particular attention, a point laid stress on in our consideration. The study of the physical behaviour of these subnuclear particles led to distinguish three types of interactions: the strong, the electromagnetic and the weak interaction. As the names suggest these interactions differ in their respective strength.
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