In the world of research, diffusion is understood as a process in which tiny particles disperse uniformly throughout a gas or liquid. Although these media are made up of individual particles, diffusion is perceived as a continuous process. So far, the effects of an individual collision between particles – the cornerstone of diffusion – had not been observed. Now, physicists in Kaiserslautern and Erlangen have succeeded in observing the fundamental steps of diffusion by individual atoms in a gas and have provided a theoretical description of this mechanism. The study has been published in the renowned journal Physical Review Letters.