The Lagoon Read online

  When Aristotle does biology one senses his solitude. Of course he could talk to Theophrastus and, later, his students; but who among his contemporaries cared about sponges and suchlike – cranky old Speusippus? Maybe. Astronomy was different. By the mid-fourth century there was a network of mathematical astronomers that spanned the Hellenic world.* Two of them, Eudoxus of Cnidus and Callippus of Cyzicus, were at the Academy with Aristotle. The former was a first-class mathematician who had Archytas of Tarantum, said to be the founder of mathematical mechanics, as a teacher.

  Aristotle is uncharacteristically generous towards them. This is the verbal theorist’s deference towards colleagues who can actually do the maths. (How well I know it.) In any event, when Aristotle needs a geometrical model of the cosmos, he just elaborates theirs. This model postulated a spherical Earth* located in the middle of a series of concentric spheres in which the heavenly bodies were embedded. The system (or, rather, systems since Callippus improved, or at least modified, Eudoxus’) was complex and designed primarily to explain the retrograde motion of the ‘wanderers’ (planētai) – the peculiar way in which they danced across the night sky instead of progressing across it as the regular stars did.*

  The details need not concern us; as far as Aristotle is concerned it isn’t natural science at all. The models produced by the mathematical astronomers may describe heavenly events; they may ‘save the appearances’ (phainomena) – the phrase is attributed to Plato – and, while that’s important, it’s not enough. The stars aren’t just mathematical constructs, they’re natural bodies; natural bodies are the objects of natural science; and natural science needs causal explanations. What are the heavens made of? Why do they rotate? It’s not just that the astronomers had no answers to such questions; they didn’t even think to ask them.

  Of all the natural entities in Aristotle’s cosmos, the celestial bodies – the moon, sun, planets and, most especially, the stars – are most perfect and divine. They are, he admits, the hardest to study: they are so far away and we know so little about them, but that should not stop us from trying to understand them. When we tackle hard problems we should be content with even modest results. We find more delight in even a partial glimpse of a beloved’s face than the plain sight of commonplace things.

  RETROGRADE MOTION OF MARS AGAINST THE STARS, AUGUST 2003

  Aristotle tackles the celestial bodies in The Heavens. He claims that the heavenly bodies, indeed the spheres in which they are embedded, are made of a unique substance – the ‘first element’ – to prōton stoicheion, traditionally called aithēr. This brings the total number of Aristotelian elements to five. Just as the four sublunary elements have a natural principle of change and rest, aithēr does too. Here, as always, when Aristotle wants eternity he looks for a circle; he thinks it’s the simplest of all movements.* So he postulates that aithēr’s natural motion is circular but that it has no natural place of rest. Since it moves in a circle (rather than up or down) it is weightless. It isn’t part of the four-element transformational cycle, so it’s indestructible too.

  Elemental aithēr was controversial stuff. In The Timaeus Plato gave the conventional view that the stars were made of fire. Proclus, writing in the fifth century AD, said that the Platonists thought aithēr positively barbaric. Some of Aristotle’s Peripatetic successors abandoned it too. (It caught on in the Middle Ages.) Yet his reasons for dreaming it up were cogent. Were the stars made of some combination of the conventional sublunary elements it would be hard to explain the beautiful regularity of their movements – aithēr does so effortlessly. Aithēr also gives eternal existence. It means that the stars don’t have to contend with the internal elemental turmoil that ultimately destroys everything on Earth, including us.

  The strangest aspect of Aristotle’s cosmology is not, however, its chemistry, but his application of teleological – functional – reasoning to the heavens. To say that the celestial bodies rotate about the Earth because they’re made of aithēr is merely to give the material and moving causes. But, as always, Aristotle also wants a final cause. The celestial bodies rotate for the same reason that animals and plants reproduce: for the sake of being eternal. It’s an odd claim – why should the stars move for the sake of anything? Odd it may be, but it’s just a start.

  Aristotle investigates the mechanism of their movement. He wants to show that each star is not motoring along under its own steam, but that they’re being collectively transported in a single, rotating aithēr sphere. He provides some evidence for this: they all move in synchrony, so transportation seems like the most economical explanation – he compares them to ships being carried in a stream. Moreover, if they did move themselves, we’d see them rolling; but the moon doesn’t roll since we can always see its ‘face’. And here’s another argument: if they moved themselves, then they should have locomotor appendages – feet, fins or wings – but they don’t. (Aristotle does not bother to say that no one has seen wings sticking out of the moon. I suppose it’s obvious.) But it cannot be, he continues, that nature has just neglected to give them locomotor appendages; after all, the celestial bodies are perfectly designed to do what they do – far better (he asserts) than any animal is. So their method of locomotion must be of a sort that does not require appendages: transport in a crystalline sphere of aithēr.

  It is easy to translate Aristotle’s teleological explanations of animal bodies into the adaptationist design-talk of modern biology. But celestial bodies? Planetary science tells us that the moon is round and orbits the Earth because brute physics made it so; the fact that it lacks wings doesn’t even arise. But that’s the point. For us, the sun, moon and stars are inanimate; for Aristotle they are alive – as alive as a bee, an elephant or you. In a sense they are more alive; they are the most perfect of all living things. The cosmos as a whole may not have a soul – but a star does.

  Aristotle’s celestial biology is a little vague – how could it be otherwise? – for sometimes he suggests that it’s not the stars (or planets) themselves that are alive, but the spheres in which they’re embedded. Stars or spheres, there’s definitely Life Out There. Is this another of Aristotle’s cosmological novelties? ‘But we think of them only as bodies, and units that have an order, but nevertheless are wholly without soul. However, they have to be accepted as possessing life and activity.’ He even extends his zoological ladder-of-perfection upwards. The stars, or their spheres, are by virtue of their motions – and hence the means by which they achieve their goal – the most perfect; the planets, sun and moon are, in decreasing proximity to Earth, less so. The motionless Earth has no goal at all.

  Like any plant or animal, the celestial bodies are, in general, designed to fulfil their own goals. But they are not entirely indifferent to sublunary affairs. The stars, unvarying in their orbits, have a very simple motion, but the other celestial bodies do not. The planets retrograde and the sun not only moves east to west but also has a secondary, west-to-east movement along the ecliptic. These are precisely the movements that the mathematical astronomers’ models sought to describe. Aristotle, however, wants to give these more complex movements a purpose too. The secondary motions of the sun and the moon drive the seasons on Earth, and so the sublunary elemental cycle that stops the world from turning into an onion. But, he seems to suggest, this isn’t just the consequence of material necessity, it’s the reason that these secondary motions exist. Note the direction of causality. The sublunary elements do not merely cycle because the sun has secondary motions; the sun has secondary motions in order to make the sublunary elements cycle. Aristotle appears to be invoking the principle of conditional necessity from his zoology, which claims that the features of a living animal are designed to fit with each other, to the cosmos as a whole. The household analogy of Metaphysics λ, 10, then, is not just about how sublunary organisms depend on each other for their existence, but how they depend on the actions of the creatures orbiting the Earth. Entities both higher and lower in the chain of being are connected to ea
ch other by a criss-crossing network of benefits. Aristotle’s ecology is literally cosmic in scope. That is why, in Generation & Corruption, he calls the sun ‘the generator’ and why, in the Physics, he amends his usual slogan ‘a man gives rise to a man’ to ‘a man and the sun give rise to a man [italics mine]’. This isn’t just a statement about the connectedness of all things; it’s an assertion of cosmic purpose.

  The whole scheme is magnificently absurd. Setting aside the claim that the celestial bodies are alive, even the weaker claim of a designed universe strikes us as strange. No astronomer believes that any of the universe’s features – moons, planets, stars, nebulae, black holes, supernovae, galaxies – show evidence of design. Outside biology, teleology has no place in the scientific explanation of cosmic order. The universe just is.

  Or is it? There is, at the heart of modern physics, a deep mystery. The Standard Model of particle physics and the λCDM cosmological model* that explain our universe so well – at least between scales of 10−21 and 1025 m – contain some thirty input parameters, for example, the masses of the elementary particles and the strengths of the three fundamental forces (electroweak, strong nuclear and gravity). Many are dimensionless and take apparently arbitrary values – except that, were they to vary from observed, the universe as we know it would not exist. To give but two examples, the cosmological constant, λ, is approximately the mass-energy density of one hydrogen atom per cubic metre. Quantum theory says it should be much greater, but if it were our universe would have expanded so quickly that neither galaxies nor we would be here. Again, neutrons are ~0.1 per cent heavier than protons: were the reverse true, protons would decay into neutrons, hydrogen would be unstable and conventional chemistry would not exist. This is known as the ‘fine-tuning’ problem.

  Some physicists have tried to explain cosmic fine-tuning away by invoking the ‘weak anthropic principle’ – the idea that, were the physical constants of the universe not such that stars, planets, life and intelligent life could form, we wouldn’t be here to wonder at the fact that they have. That is true, but does not solve the problem. If there is only one universe, and only a few solutions in the parameter space consistent with the evolution of sentient life, the odds against nature having got everything right must be, literally, astronomical. As Aristotle said, attacking Democritus et al. – ‘They [the materialists] assert that chance is not responsible for the existence or generation of animals and plants . . . and yet at the same time they assert that the heavenly sphere and the divinest of visible things arose spontaneously, having no such cause as assigned to animals and plants.’ The empirical regularities that puzzle Aristotle and modern cosmologists are different: the root problem is the same.

  Let’s accept, ex hypothesi, that the cosmos shows the signature of purposeful order, the hallmark of design. Where does it come from? There are three, and only three, possible answers. The first is to appeal, as Plato did and Christians still do, to a beneficent creator who arranged things just so. The second is to appeal, as Democritus did and Epicurus would, to an infinite universe – infinity solving all low-probability dilemmas. The first can be discarded; the second I have no views on, though some cosmologists believe it to be true.* As a biologist, however, I like the third for it depends on the only known mechanism capable of creating order from disorder: natural selection.

  This is the reasoning behind Cosmological Selection Theory, which proposes the existence of a population of universes – a multiverse; that these universes reproduce, that they do so with unequal success, and that they transmit their physical constants, allowing for some mutation, to their progeny universes. It’s nothing more or less than cosmic Darwinism and an easy route to a universe which, depending on the fitness function, has any non-lethal combination of parameter values that you please. One multiverse theory holds that universes give birth to baby universes via black holes. In that case, the number of black holes in our universe (millions) would be a design feature. The plausibility of the physics need not detain us; but, granting them, or some similar scheme, it is clear that natural selection among universes will work. If it has, far from being the mere product of brute material necessity, some of the features of the universe would be as teleologically explicable as the parts of an elephant.

  Such a cosmos would have a purpose. In such a cosmos, Aristotle would surely be at home. And yet he would reject a selectionist explanation for its origins, just as he would reject a creator and chance. Ask Aristotle, how did the cosmos come to have its purposeful features?, and he would say: that’s a meaningless question since the cosmos didn’t come to be. It just is and was and always will be, forever and forever and forever. Of all his theories this, I think, is the one that we most struggle to understand.

  CIII

  WE ARE APPROACHING GOD. I have mentioned, in passing, how Aristotle thinks that stars, humans and even bees are ‘divine’, but perhaps you took that merely as a façon de parler, Aristotle’s way of describing beauty, high intelligence or a complicated social life. God has even cropped up once or twice by name, but perhaps you thought that He was just a metaphor for something like Plato’s absolute good. If so, that is doubtless my fault. I have kept Aristotle’s theos in the shadows. It may even be that I have done so deliberately; that I have been reluctant to reveal the degree to which my hero’s scientific system is riddled with religion. Yet it is. In truth, God has been with us all this time.

  Why does Aristotle think that the stars are alive? He certainly doesn’t give any evidence for it. In The Soul he says, ‘By life we mean the capacity for self-nourishment, growth and decay’ – but the stars, he also says, do nothing of the sort. They neither have nor need organs. True, he says that they have souls and that they’re enjoying themselves up there, but how does he know? It’s mere assertion. It’s a bizarre stance to take – at least it is for a scientist who’s so cautious about the reproductive habits of bees. He seems to be star-struck:

  The reasons why the first body [aithēr] is eternal and not subject to increase or diminution, but unageing and unalterable and unmodified, will be clear from what has been said to anyone who believes in our assumptions. Our theory seems to confirm experience and to be confirmed by it. For all men have some conception of the nature of the gods, and all who believe in the existence of gods at all, whether barbarian or Greek, agree in allotting the highest place to the deity [italics mine], surely because they suppose that immortal is linked with immortal and regard any other supposition as inconceivable.

  Which shows that he’s God-struck too.

  There is a passage in the Metaphysics where Aristotle undertakes some religious archaeology. Our remote forefathers have, he says, handed down to us a tradition that the heavenly entities are gods and that the divine encompasses all nature. Later, however, mythical elements were added on – the zoomorphic and anthropomorphic gods of popular religion. But these were merely invented for ‘the multitude’ and because they were ‘useful’. (I take this to mean that the mob needed pretty statues to worship, and the state needed religion to control the mob.) But, he continues, we should separate the original ‘divine utterances’ from these later accretions . . .

  Aristotle has invented a new theology that seamlessly interweaves prehistoric superstition with cutting-edge science. He repeatedly refers to some antique belief about the gods – that they are located in heaven, are immortal or unchanging – and then shows, with a flourish, its consistency with cosmological theory. The reason, then – the only reason as far as I can tell – why Aristotle thinks that the celestial spheres are alive is because he thinks they’re gods.

  Aristotle says that theology is not a branch of natural science. It is, in his terms, first philosophy, a branch of our metaphysics; natural science is second philosophy. Different domains of knowledge, he also says, should be kept firmly apart because they depend on different first principles. Yet in his relentless drive for intellectual Lebensraum he marches across any disciplinary frontier he pleases. He discusses t
he nature of the gods not only in the Metaphysics but also in The Heavens, The Soul, Generation & Corruption and the Physics. They even appear in The Movement of Animals.

  It can hardly be otherwise since the functioning of the world depends on them in so many ways. The rotations of celestial spheres are the ultimate moving cause of all natural sublunary change. As moving causes the celestial spheres can keep the cosmos going whether they’re dead, alive or divine. But Aristotle also relies on them to give its creatures their goals; and for that they must be gods. Aeschylus died as the unwitting instrument of an eagle’s ends. Her goal (we may suppose) was merely to feed the tortoise to her ceaselessly ravenous brood. In doing so she sought to emulate the eternal motion of the stars – not the petrified perfection of crystalline spheres, but the immortality of living deities. All she sought was a little slice of for ever. So, looking to our mates, do we all.

  What do the motions of the god-spheres depend on? It may be thought that they depend on nothing: they’re gods, after all. Besides, they’re built of aithēr that just naturally moves in a circle. That, indeed, seems to be the theory that Aristotle gives in The Heavens; in the Metaphysics and Physics, however, he gives another, or perhaps it’s just a shift in emphasis. In this second version celestial spheres do not move themselves. Their divinity is downgraded. Aithēr fades into the background and a host of mysterious entities appear on stage: the ‘unmoved movers’.

  The unmoved movers are the new deities. The spheres were almost mundanely comprehensible. Any science-fiction fan will take AU-scale sentient entities composed of exotic matter in his stride. The unmoved movers, by contrast, are gratifyingly abstract and paradoxical. There are said to be fifty-five of them, but also just one. They power the celestial spheres yet are utterly static themselves. They do this despite being indivisible, devoid of parts or even bodies. They are, in fact, immaterial. Aristotle means that they’re not made of any physical substance.