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Some useful fictions

The object of this article is not to encourage scepticism but rather to combat it by attempting to distinguish between concepts which correctly express physical reality and those deliberate fictions which aid visualization or simplify calculations. At the outset a distinction needs to be made between idealizations, models and fictions. An idealized object, such as a perfect gas or a perfectly smooth wall, is not found in the observed world but it is not a contradiction of it either; it might be regarded as a higher limit to empirical realization. A model, such as the Bohr atom or the drop-model of the nucleus, is of uncertain representative value yet it is retained as a useful tool in discovery. A fiction, such as a magnetic pole or centrifugal force, is a deliberate falsification of reality which has been found useful. It is this very usefulness which is the criterion whether it should be retained or not. Fictions are rather dangerous guests in physics in that a constant vigilance is required to remember their fictitious character, a vigilance that is all too easy to lose. If these convenient myths are tacitly presented to the intelligent student as real it can cause him to unconsciously abandon the effort to make physics intelligible and coherent beyond a certain point. The present writer does not subscribe to the view that the whole qualitative content of physics is merely a useful mental  construct or model without  any necessary reference to reality. A selection, by no means exhaustive, is given of some fictions which are employed in sixth form physics and each is followed by a brief analysis. It is hoped that this may contribute to the constant battle to make physics ever more clear and comprehensible.