Quantum Field Theory
Quantum Field Theory saw its advent in the early thirties as a combination of three substantial elements of physics - Quantum Mechanics, Special Relativity and Classical Field Theory. Initially, Quantum Field Theory, in the shape of Quantum Electro Dynamics, was only applied to the electromagnetic force-fields, but through the years it became evident that the strong and weak forces as well as matter and other phenomena could be treated in a like manner. At this site, we shall not get into technical details but confine ourselves to the conceptual understanding of the key-issue - quantum fields.
What is a field?
Mathematically, a point is an entity which has no extent but is infinitely small. A mathematical field is an infinite set of such points that are continuously distributed throughout space. In physics, one or other quality is attributed to each point so the corresponding field thus becomes a medium of this quality. Depending on which quality is attributed the field may be a force field, a matter field, an energy field, etc. - Now, probably this concept of infinite sets of infinitely small entities is hard to grasp for the uninitiated but do not despair. The important thing to remember is that a field is a phenomenon which is continuously distributed throughout space.
What is a quantum field?
In Quantum Field Theory one applies certain mathematical operations to the fields whereby these become quantized. The immediate consequence of quantizing a field is that certain subsets of the points, constituting the field, are restricted to be finite and discrete quantities of the attributed quality, rather than the quality being uniformly distributed throughout the whole field. Such discrete subsets of a field are called field quanta - or quanta for short. Each kind of field has its own kind of quanta, which have been given a more or less fanciful name. E.g., photons are the quanta of the electromagnetic force-field, gluons are the quanta of the strong force-field, quarks and electrons are quanta of matter-fields, etc.
What is a quantum?
Unfortunately, the term 'particle' is often used as a synonym for 'quantum'. This unhappy mixing of concepts has served to obscure the circumstance, that through the 20'th century a brandnew world-view has gradually emerged, totally different from the world-views of preceding times. Let us be specific: A particle is a discrete entity residing or moving in an empty region of space - usually called vacuum. The particle's intrinsic substance and qualities are totally independent of this vacuum. A field quantum is a discrete entity residing or moving in a continuous medium. Its intrinsic substance and qualities are direct manifestations of this medium. Although all branches of physics agree conceptually, that the "elementary particles" are not particles but field quanta, it is almost exclusively Quantum Field Theory and General Relativity (gravitational field theory) that actually take the immanent field properties into account. However, this is mainly a matter of technical pragmatism. The mathematical complexity of field theories is tremendous and the phenomena, encountered in other branches of natural science, can be handled quite well without bothering about field properties.
Having thus settled the technical issues, what kind of world-view is that has gradually emerged through the 20'th century? - Well, since the times of the ancient Greeks the Western world-view has been dominated by the idea that everything in the physical universe was made up by minute, indivisible building blocks of a fixed size and outline - i.e. particles. From its advent until the early nineteen-thirties the main course of natural science was to detect still smaller representatives for the basic building blocks. Nevertheless, the overall, conceptual yield of Quantum Field Theory is a world-view according to which, everything in the universe is nothing but the appearances of vibrating, interacting fields. - Is there, perhaps, some kind of field which is more fundamental than any other field? - Quantum Field Theory says yes. On the next pages this issue is discussed.
