Similitude and Model Experiments

Abstract

Somewhat unprecise and stretching the correct definition, a physical model is a mapping of Nature or at least of a subprocess that occurs in Nature or in our world of experience to smaller scale. “Projection” instead of “mapping” would be the better denotation, since some information is lost in the mapping. It is not necessary that the processes describe a physical incidence, however in this chapter we shall limit ourselves to physical systems. Naturally, every theory that describes processes of any kind, already represents a model; the theory would better be called a model, and it is imputed that the theory describes the processes in a certain sense and is able to also predict them adequately. The restriction that is imposed by such a theory is the fact, that it only adequately describes partial facts of the reality, those which are important, and that it ignores unimportant facets or even may describe these erroneously. In this sense, every theory or model is a projection of Nature, which enjoys only some similarity with the latter. Its intention is the determination and possibly the forecast of those physical quantities which are thought to be important as derivatives on the basis of the presentation of external sources and of initial conditions. The problems are generally formulated as initial boundary value problems.