Cheer up: things can only get worse

If you have ever agonised over the Second Law of Thermodynamics, stop now. Peter Atkins says it's really quite simple, and nothing to worry about ot knowing the Second Law of Thermodynamics is like never having read a work of Shakespeare,' wrote C.P. Snow in his The Two Cultures. I suspect that in the light of modern education the remark is now completely meaningless, but I can presume that most readers of this journal will understand its general thrust. The Second Law is held up by many as, or just presumed by most to be, the epitome of incomprehensibility. But is it? And why do people make such a fuss about it?

I write about it today because the editor of this magazine challenged me to name the single most important scientific insight granted to mankind. This is it.

The law is easy to grasp, as are all really great laws. All it states is that things get worse. Few, I am sure, would argue. Of course, scientists have been able to refine this awesomely simple idea, and have expressed it more precisely. In doing so, they have endowed the banal with astonishing potency. They have exposed the spring of the universe, the motive power that drives all change, the engine of creation.

Thermodynamics, of which the Second Law is a central component, has had a somewhat confused history dating from when people started to think about how to improve the efficiency of early steam engines and when the nature of heat was the hot topic of the day. Few people regard the subject in its true light, which is to illuminate the everyday, from the delicate unfolding of a leaf to the formation of a thought (not to mention the building of great power stations and the efficiency of every kind of engine).

The Second Law was first formulated by two 19th-century quasi-geniuses who did what the best scientists do: they noticed the obvious. William Thomson, later Lord Kelvin, stood in front of a steam engine and thought to himself, 'Damn me, the blessed thing wouldn't work if the heat hadn't got anywhere to escape to.' That became, with appropriate refinement, the first statement of the Second Law. Over in Germany, Rudolph Clausius, reflecting glumly on his now cold cup of coffee, noticed something else, turned to his neighbour and said, 'You know what? Heat doesn't flow uphill.' The neighbour probably moved gently away, as anyone might, but Clausius published his observation, and it became the second statement of the Second Law.

Noticing the obvious is a powerful technique of science. The biochemist Albert SzentGyOrg captured the essence of this remark very well when he said that science consists of seeing what everyone else has seen but thinking what no one else has thought. The simplicity of Kelvin's and Clausius' observations resulted in a surge in the quantitative treatment of heat engines and a deep and effective understanding of their efficiency.

A deeper insight into the underlying mechanism of the law came from the short-sighted Austrian scientist Ludwig Boltzmann, who saw further into the nature of matter than most of his contemporaries. Depressed at the obduracy of stupidity, he hanged himself when he was confronted with opposition and disbelief.

Still, truth will out, in science at least, and we now know that Boltzmann was dead right. Broadly speaking, and this is where the things-get-worse bit of the story gets elucidated, matter and energy tend to spread out in disorder. That is all there is to understand about why anything happens at all: spreading out is the spring of the universe. All change is driven by the tendency of matter and energy to disperse. If you are happy to regard this tendency as a sinking into corruption, then — in that guarded sense — corruption is the spring of change.

What I have described accounts for a gas spreading out to fill the available space, because the gas molecules are dashing about chaotically (the word 'gas' comes from the same root as 'chaos). Although they might be bunched up in one corner of the room initially, after a few milliseconds they are everywhere, and will never be found back simultaneously in the original corner, or any other corner for that matter. That your forgotten cup of coffee is getting cold while you are gripped by this account is due to the molecules in the cup bumping against the atoms in the walls, jostling them into vibra

tion, then those atoms jostling the atoms in the table and the surrounding air into vibration, and so on, out to China, or wherever.

Now for the really super-important point: that spreading out can be constructive. Out of disorder, order can rise. The key idea is that we can tap into the dispersal, and use it to build. The only constraint is that the overall outcome can't be more ordered than before. The order we introduce into the universe by piling brick upon brick cannot be greater than the increase in disorder of whatever is driving the construction. Although structure emerges locally, and locally things might thereby improve, ineluctably overall things get worse. Any orderly construction is but a local abatement of chaos in the ocean of increased disorder.

Let's think of a real example. When fuel burns in an engine, the long spindly fuel molecules are broken up and spread away as lots of little carbon dioxide molecules. At the same time energy is released in the burning, and jostles away in disorder. The design of the engine, the piston and all the other gubbins is such as to harness this dispersal, and cause it to drive the raising of bricks or whatever construction is going on.

The same principle applies to any kind of construction, including the construction of human bodies and the thoughts they have. A sandwich is fuel, and its metabolism in the body is exactly like the combustion of a fuel. Instead of pistons and metal parts, we have organic gubbins, enzymes, and instead of bricks we have amino acids. Instead of walls being built to form cathedrals, inside us amino acids are piled on one another to form proteins. Thus our molecules grow, and with them so do we. We are the efflorescence of corruption, driven by the dispersal of matter and energy. We too are local abatements of chaos.

Our thoughts are the manifestation of chemical processes going on in that elaborately twisted and convoluted test-tube that we call the brain. Those processes are marshalled by metabolism, just as amino acids are marshalled, just as bricks are marshalled. Thus, creativity, the piling of thought upon thought, is driven by corruption. Words are marshalled into poems, notes are marshalled into symphonies. . . there is nothing that is not driven forward by corruption, even politics.

Oh, I forgot to mention entropy. Everyone understands `energy', until they are asked to explain what it means. Everyone is frightened of 'entropy', fearful of its mystical sophistication. In fact, entropy is just a measure of disorder (admittedly in a slightly erudite way), and the greater the disorder the greater the entropy. So as a classier way of saying things get worse, we could say, 'Entropy tends to increase'. That is the Second Law.

Entropy makes the world go round. As this event and then that result in increased disorder (entropy), their coupling to other events results in construction, physical construction. biological construction, and mental construction. The Victorians were distrustful of the concept of entropy, for they considered that God had endowed the universe with a variety of properties in judiciously chosen quantities that no amount of man's fiddling could increase. That there was a property — disorder — which with man's meddling resulted in an increase of the initial endowment was distasteful and quite unacceptable.

In a certain well-defined sense, we now know that there can never be an energy crisis, for the quantity of energy in the universe is absolutely fixed, and however profligate we are with its deployment, we cannot change its total amount. We should realise, instead, that there is a looming entropy crisis. For the world to move forward — for events to occur — we need low entropy, compact accumulations of energy (oil is an example). Such compact accumulations can release their energy into the surroundings, and we can tap into that dispersal (with our power stations and our intestines). When such accumulations have been exhausted, we shall still have exactly the same amount of energy, but we shall be up to our ears in entropy. When entropy can no longer increase, when the flood of corruption (in the sense in which I have used the term) is stemmed, the world will be dead.

Peter Atkins is professor of chemistry at the University of Oxford. His recent books include Galileo's Finger: the Ten Great Ideas of Science (OUP, 2003).