Colloidal suspensions, Brownian motion, molecular reality: a short history

In the first decade of the 20th century, nearly a hundred years of work on the phenomenon of Brownian motion culminated in theory and experiments that demonstrated irrefutably the discontinuous or molecular nature of matter. Colloidal suspensions and the phenomenon of Brownian motion thus became the key to confirmation of the ‘new world-view’ of statistical mechanics, the statistical basis of thermodynamics. One may conveniently identify four ‘stages’ in the historical development of ‘Brownian motion science’, characterized in turn by discovery, observation, theoretical prediction, and quantitative confirmation. We are living, of course, in the fifth stage, that of application: the modern discipline of ‘soft matter’.