Discovery Science: Thermodynamics – Order and Disorder

Earth Science: Thermodynamics – Order and Disorder

When we pour milk into a cup of coffee, it mixes forming a light brown liquid. The opposite—the spontaneous separation of coffee and milk—has never been observed, although it is theoretically possible

The spontaneous separation of a mixed liquid is possible, although it does not seem at all obvious, according to the laws of thermodynamics. The concept of thermodynamics includes a condition or value called entropy (often identified with “disorder”), which was first identified in the field of chemistry.

Entropy helps balance the energy equations for certain chemical reactions: for instance, a gas has higher entropy than a liquid; warm objects have higher entropy than cold ones; and the entropy of a mixture is higher than that of an “orderly” system, which is separated into components. The key to understanding entropy was discovered by Ludwig Boltzmann (1844-1906). His realization was that entropy describes the probability of a particular state within a system.

Thus, there may be only one way to sort the papers on a desk by size and content, but there are countless ways to scatter them in unorganized piles. Similarly, milk and coffee molecules can be distributed in many more ways as a mixture than if they were neatly divided into layers. For this reason, unorganized conditions are generally more likely. In fact, the number of atoms in a cup of coffee is so unimaginably large that the probability of spontaneous separation is less than 1 in 10^(-20)

The second law

Our knowledge about entropy is summarized in the second law of thermodynamics: entropy (or “disorder”) in a closed system never decreases. If we look at the universe as a whole, then total entropy must always increase over time. This means that sometime in the far future, structures such as galaxies, planetary systems, and even chromosomes can be expected to break up.

The thermodynamically stable final condition would be a uniformly mixed cloud of assorted particles at a constant temperature, permeating the entire universe. Many multiples of the current age of the universe will have to pass before this state, called “heat death,” is reached, a state where all energy will be evenly distributed through- out the universe, a universe that will be barely warmer than absolute zero.


Living things are highly intricate, orderly structures, whose complexity has continually increased through evolution. We live viewed on a cosmic scale— in a paradise of order. The Earth has been warmed by the sun for billions of years and we are far from reaching thermal equilibrium.

The complex self-organizing system called life has plenty of time to avoid the inevitability of entropy and heat death.