peter_atkins's picture
Emeritus Professor of Chemistry, University of Oxford; Author, What is Chemistry?

Why Things Happen

There is a wonderful simplicity in the view that events occur because things get worse. I have in mind the Second Law of thermodynamics and the fact that all natural change is accompanied by an increase in entropy. Although that is in my mind, I understand those words in terms of the tendency of matter and energy to disperse in disorder. Molecules of a gas undergo ceaseless virtually random motion, and spread into the available volume. The chaotic thermal motion of atoms in a block of hot metal jostle their neighbors into motion, and as the energy spreads into the surroundings so the block cools. All natural change is at root a manifestation of this simple process, that of dispersal in disorder.

The astonishing feature of this perception of natural change is that the dispersal can generate order: through dispersal in disorder structure can emerge. All it needs is a device that can link in to the dispersal, and just as a plunging stream of water can be harnessed and used to drive construction, so the stream of dispersal can be harnessed too. Overall there is an increase in disorder as the world progresses, but locally structures, including cathedrals and brains, dinosaurs and dogs, piety and evil deeds, poetry and diatribes, can be thrown up as local abatements of chaos.

Take, for instance, an internal combustion engine. The spark results in the combustion of the hydrocarbon fuel, with the generation of smaller water and carbon dioxide molecules that tend to disperse and in so doing drive down a piston. At the same time the energy released in the combustion spreads into the surroundings. The mechanical design of the engine harnesses these dispersals and through a string of gears that harnessing can be used to build from bricks a cathedral. Thus, dispersal results in a local structure even though overall the world has sunk a little more into disorder.

The fuel might be our dinner, which as it is metabolised releases molecules and energy that spread. The analog of the gears in a vehicle is the network of biochemical reactions within us, and instead of a pile of bricks molded into a cathedral amino acids are joined together to generate the intricate structure of  a protein. Thus, as we eat, so we grow. We too are local abatements of chaos driven into being by the generation of disorder elsewhere.

Is it then too fanciful to imagine intellectual creativity, or just plain inconsequential reverie, as being driven likewise? At some kind of notional rest, the brain is a hive of electric and synaptic activity. The metabolic processes driven by the digestion of food can result in the ordering, not now of brick into cathedral, not now of amino acid into protein, but now current into concept, work of artistic expression, foolhardy decision, and scientific understanding.

Even that other great principle, natural selection, can be regarded as an extraordinarily complex reticulated unwinding of the world, with the changes that take place in the biosphere and its evolution driven ultimately by descent into disorder. 

Is it then any wonder that I regard the Second Law as a great enlightenment? That from so simple a principle great consequences flow is, in my view, a criterion of the greatness of a scientific principle. No principle, I think, can be simpler than that things get worse, and no consequences greater than the universe of all activity, so surely the Law is the greatest of all?