Are Languages like Atoms? On Modelling Language Spread as a Physicist

In physics, the spread of particles such as atoms is called diffusion. The same term is employed in linguistics to describe the spread of language features or languages as a whole. In this paper, we investigate how models for physical diffusion can be transferred to linguistics to study language spread. We review the different ways of describing physical diffusion and then look at two types of models to study language spread. By examining the differences and similarities between speakers, languages and atoms, we show that it is important to be clear about what is being modelled: languages or speakers, as these are quite different but cannot be completely separated - languages cannot exist without speakers and vice versa.