Science: Ugly Nature, by Jim Holt

GRANTA 102  

Arguing with global warming sceptics over the years, I have noticed an interesting evolution in their case. First, I heard that no warming was taking place. Then I heard from them that yes, there might be warming after all, but that it was not caused by human activity. Then I heard that yes, there might be global warming, and yes, it might be caused by human activity, but that its effects, on the whole, will actually benefit humanity. Sure, global warming might result in a bit of severe drought here and there, along with rising sea levels, more destructive hurricanes and the extinction of species. But it will be good for American retirees, allowing them to stay in Minnesota for the winter rather than having to travel all the way to Florida. It will open up the Northwest Passage to shipping. Canada will become the world’s hot new wine region.

Cost-benefit analysis is a tricky business, mixing, as it does, empirical science with individual values. If your preferences are weird enough, you might actually enjoy living in a world where the average temperature is a few degrees higher than it is today. As David Hume remarked, ‘’Tis not contrary to reason to prefer the destruction of the world to the scratching of my finger.’) Yet there is one point of view from which global warming is incontestably bad: the aesthetic point of view. A warming planet is a planet that’s getting uglier. I’m not talking about the beauty of polar ice caps or coral reefs, but something more abstract and profound, something that goes right to the very nature of life and its relation to the rest of the universe.

What exactly do we get from the sun? Ask most people and they’ll probably say ‘heat’ or ‘energy’. But this is inaccurate. It’s not really energy (of which temperature is a measure) that the earth has been amassing from the sun these five billion or so years. What terrestrial nature actually sucks out of the sky is order; or, to put it more abstractly, information. Properly viewed, global warming is a build-up of disorder – of information-destroying ‘noise’.

The realization that nature imports order rather than energy from the sky is a relatively new one. In 1944, the Austrian theoretical physicist Erwin Schrödinger wrote a little book called What is Life? A couple of decades earlier, he had discovered the famous Schrödinger equation, the key to the new quantum theory. Now, as the heroic age of physics was giving way to that of molecular biology, he focused his attention on life.

Living things are made of matter, Schrödinger observed, yet they seem to violate the laws of physics. One of the most basic of these laws is the second law of thermodynamics, a universal tendency towards disorder. Entropy – a mathematical measure of the disorder present in a system – is always on the rise. Left on their own, things fall apart, run down, become inert; they tend towards an equilibrial state of chaos and dissolution. This is a matter of cruel probability: as we all know from our own domestic lives, there are vastly more ways for things to be disordered than to be ordered, so it is far more likely that things will slip from orderly to disorderly rather than the reverse.

But living things seem to buck this trend towards chaos. They ‘keep going’ much longer than inanimate things, putting off the moment when they reach that dangerous state of disorder known as death. How, Schrödinger asked, do living things cheat the second law of thermodynamics? Well, the second law says that entropy always increases in any system that is left alone; that is isolated from outside influences – the universe as a whole, for example. But living things are not isolated.They are always exchanging stuff with their environment. (Indeed, the German word for metabolism is Stoffwechsel – ‘stuff exchange’.) What is this stuff? It’s not matter: unless you are a child who is growing or an adult who is getting fat, your material content stays the same over time. It’s not energy, either. True, animals do use up some energy moving around (unlike plants), but most of the energy we take in is radiated back into the environment in the form of heat. The crucial stuff – Schrödinger concluded – that a living thing absorbs from its environment is order.

Animals eat food containing highly ordered organic compounds and then return the material back to the environment as disordered waste (not entirely disordered: it’s still of some value as manure). By feeding upon order, we offset our body’s internal tendency towards greater entropy.We get these highly ordered organic compounds from green plants, which assemble them from (less ordered) water and carbon dioxide through the process of photosynthesis. Thanks to their chloroplasts, green plants are able to absorb what Schrödinger called ‘negative entropy’ from sunlight and fix it in material form.

Why, though, should the sun be a source of orderliness? Schrödinger did not say. But you can get a clue by going outside on a clear day and looking up. The sky is quite neat. It’s nicely organized into a bright little disc surrounded by a lot of blue. If the sun were messily spread out over the entire sky, daytime and nighttime, it would be useless to life on earth. Because of this orderliness, the sky is our friend in the struggle against entropy.

Terrestrial nature drinks up the sky’s orderliness in a beautifully simple way. During the day, the earth gets energy from the sun in the form of photons of visible light. At night, the same amount of energy is dumped back out into space in the form of infrared photons, otherwise known as radiant heat. Taken individually, visible-light photons are more energetic than infrared photons. (The energy of a photon is determined by its wavelength: the shorter the wavelength, the higher the energy.) So, if the total incoming/outgoing energy is to balance, there must be many more energy-poor photons leaving at night than energy-rich photons arriving by day. The key point is that more means messier. (In technical language, each photon represents a ‘degree of freedom’, and the more degrees of freedom, the greater the entropy.) The energy the earth dumps back into space at night is less ordered than the energy it receives from the sun during the day – just as
the waste animals excrete is less ordered than the foodstuffs they eat. While there is a net gain in order, which sustains terrestrial life in its struggle against entropy, there is no net gain in energy.

Or so we hope. Greenhouse gases trap the waste energy that should be dumped into space. They keep the biosphere from excreting disorder. Toxic entropy is building up. A warming planet is not a more energetic planet, it’s a more costive planet. It’s a more common planet, probabilistically speaking. And, if you are neoclassical in your aesthetics and prize order as the essence of beauty, it’s an uglier planet.

Disorder is the essence of global warming, just as order is the essence of life. But a mystery remains: why should the sky be a net source of order for terrestrial nature? It didn’t start out orderly. Astronomical observations over the last couple of decades have given us a snapshot of the early universe as a diffuse chaos: plenty of entropy, no information. Gradually, however, this mess began to grow more organized, as bits of it clumped together to form stars and galaxies. Information spontaneously appeared: a featureless chaos is simple to describe, whereas a galaxy is complex. And the origin of the information must have been the gravity that caused the clumping. ‘In some as yet ill-understood way,’ the physicist Paul Davies has written, ‘a huge amount of information evidently lies secreted in the smooth gravitational field of a featureless, uniform gas. As the system evolves, the gas comes out of equilibrium, and information flows from the gravitational field to the matter. Part of this information ends up in the genomes of organisms, as biological information.’

So the possibility of life was written into the gravitational field at the very origin of the universe. Somehow, the big bang was rather precisely organized. How precisely? The mathematical physicist Sir Roger Penrose has done the maths. To appreciate the odds against the early bang being smooth enough to give rise to a universe as rich in information as ours, you have to wrap your mind around this number: one, followed by a thousand trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion zeros. (That’s many more zeros than there are atoms in the universe.) In other words, for nature to be possible, the universe had to originate in a stupendously unnatural state. Otherwise it would have forever been a lifeless and chaotic wasteland. How to explain the fine-tuned smoothness? Three possibilities leap to mind. The first is that it was just wonderful dumb luck. The second is that God did it. The third is that physics will tell us once we finally arrive at a Final Theory that merges gravity, the theory of the big, with quantum mechanics, the theory of the small. My bet is on physics.

Meanwhile, perhaps we should do something about these greenhouse gases. The disorder is getting to be oppressive.