In physics, chemistry an biology, diffusion denotes the mixing of two or more substances or the net motion of a substance from an area of high concentration to an area of low concentration. The theory is that both of these result from the random motion of micro-scale individual agents (such as molecules) giving rise to net changes on the macro-scale. While originally formulated within the framework of the physical sciences, the concept of diffusion has been applied to phenomena such as the manner in which information is spread amongst a population. The chemistry definition of diffusion is the movement of a fluid from an area of higher concentration to an area of lower concentration.