Q: Why is it that if you pour one cup of milk and one cup of chocolate syrup together and mix it, you can never get back into that formation of the top being milk and the bottom being chocolate no matter how much you stir it? There is no chemical reaction, is there?

A: It might be possible to separate the milk and chocolate, but it would require energy to do so, and it might not be worth the effort. There is no chemical reaction, but there is a physical mixing which degrades the order of the system comprising the milk and chocolate. Mixing equal amounts of hot and cold water produces a similar degradation of order. These are called irreversible processes because the lukewarm water will not spontaneously reorganize into hot and cold regions any more than the chocolate milk will become unmixed. And for the same reason. These mixing processes have something in common with other types of physical changes, for example when marbles spill from a jar. While in the jar the marbles are confined to a small volume of space. Outside the jar there are many more places the marbles can be, so it is likely that they will scatter when spilled. It is extremely unlikely that they will arrange themselves in a jar-like pattern somewhere else in the room. The scattering is random, within the confines of gravity, and successive scatterings will produce different distributions of marbles. With marbles and with molecules there are many more ways to be disordered than there are ways to be ordered. In general, there are many more "out-of-place" places than there are "in- place" places. This tendency for spontaneous process to move towards disorder is quantified by the concept of entropy, which was originally formulated to explain the one-way flow of heat. The rules are simple: Entropy increases in spontaneous processes and an input of energy is required to decrease it. These rules apply not only to heat flow and spilling marbles, but to many other natural processes, such as the corrosion of metals and the noise in communications lines. In fact we spend much of our time and effort trying to maintain order in one area or another. Whether it is to preserve the integrity of information during storage, retrieval, and transmission or to prevent our cars from rusting, we must constantly deal with entropy and disorder.

Richard Brill is assistant professor of science at Honolulu Community College. Send questions to Honolulu Community College, 874 Dillingham Blvd., Honolulu, HI 96817, fax to 239-5152 , email to rickb@hcc.hawaii.edu or visit the web page at http://www.hcc.hawaii.edu/~rickb/SciDoc.html

Order and Disorder ©1996 Richard C. Brill