Small things

To join the conversation, sign up to Aeon now.

Follow us:

Small things

The discovery of a microscopic world shook the foundations of theology and created modern demons

by Philip Ball

Header mayfly nymph
'The greatness of nature, and the subtle and unspeakable care with which she works, is a source of unending contemplation'. A Mayfly nymph. Photo by Daniel Stoupin,

Philip Ball

is a British science writer, whose work appears in Nature, New Scientist and Prospect, among others. His latest book is Invisible: The Dangerous Allure of the Unseen (2014).

2,800 words

Edited by Brigid Hains

Send to Kindle

Popular now

Essay If the internet is addictive, why don’t we regulate it?

Opinion It's time to move beyond growth for growth's sake

Essay An ordinary person becomes a torturer with surprising ease

When the Dutch cloth merchant Antonie van Leeuwenhoek looked at a drop of pond water through his home-made microscope in the 1670s, he didn’t just see tiny ‘animals’ swimming in there. He saw a new world: too small for the eye to register yet teeming with invisible life. The implications were theological as much as they were scientific.

Invisibility comes in many forms, but smallness is the most concrete. Light ignores very tiny things rather as ocean waves ignore sand grains. During the 17th century, when the microscope was invented, the discovery of such objects posed a profound problem: if we humans were God’s ultimate purpose, why would he create anything that we couldn’t see?

The microworld was puzzling, but also wondrous and frightening. There was nothing especially new about the idea of invisible worlds and creatures — belief in immaterial spirits, angels and demons was still widespread. But their purpose was well understood: they were engaged in the Manichean struggle for our souls. If that left one uneasy in a universe where there was more than meets the eye, at least the moral agenda was clear.

But Leeuwenhoek’s ‘animalcules’ and their ilk indulged their opaque, wriggly ways everywhere one looked: in moisture, air, body fluids. In human semen — Leeuwenhoek studied his own, transferred with jarring haste from the marital bed — there were tadpole-like creatures writhing like eels. In 1687 the German mathematician Johann Sturm suggested that disease was caused by breathing in such invisible animals in air. In 1646 the Jesuit priest Athanasius Kircher proposed that the plague might be caused by the microscopic ‘seeds’ of virulent worms that enter the body through the nose and mouth — just a step away, it seemed, from a germ theory of contagion. Alas, the impossibility of seeing bacteria and viruses with the microscopes of the time obstructed that leap until Louis Pasteur and Robert Koch made it in the late 19th century.

The finest contrivances of man — a needle’s tip, a razor’s edge, a printed full stop — looked crude and clumsy under the microscope

Pestilence was everywhere, unseen and impossible to fend off — just like medieval demons. The narrator in Daniel Defoe’s A Journal of the Plague Year (1722) claims he has heard that if a person with the plague breathes on glass, ‘there might living Creatures be seen by a Microscope of strange, monstrous and frightful Shapes, such as Dragons, Snakes, Serpents and Devils, horrible to behold’. He admits some doubt as to whether this is true, but the message is clear: the invisible microworld is labelled ‘Here be dragons.’

Little has changed. Electron microscopes now reveal miniature viral monsters that look like science-fiction aliens, with arachnoid legs and crystal heads from which they inject genetic venom into cells. MRSA bacteria lurk unseen on hospital door handles and bed sheets. We sprinkle anti-bacterial fluids like holy water to fend off these invisible fiends.

The idea that matter might be composed of particles and processes too small to see has a long history — from the atoms of Democritus to the whirling vortices of Descartes and the corpuscles of Newton. Yet this fine-grained structure only came to seem like an ‘invisible world’ once the microscope had enabled us, first, to appreciate the intricacy with which it was wrought, and second, to identify life among the grains. When Galileo used one of the first microscopes to study insects, he was astonished and repelled, writing to his friend Federico Cesi in 1624 that:

I have observed many tiny animals with great admiration, among which the flea is quite horrible, the mosquito and the moth very beautiful… In short, the greatness of nature, and the subtle and unspeakable care with which she works is a source of unending contemplation.

The 17th-century philosopher Robert Hooke echoed this wonder at nature’s invisible intricacy. It was his book, Micrographia (1665), that put microscopy on the map. Crucially, Hooke’s volume was not merely descriptive: it included large, gorgeous engravings of what he saw through the lens, skilfully prepared by his own hand. The power of these illustrations was impossible to resist. Here were fantastical gardens discovered in mould, snowflakes like fronds of living ice and, most shockingly, insects such as fleas got up in articulated armour like lobsters, and a fly that gazes into the lens with 14,000 little eyes, arranged in perfect order on two hemispheres.

This was surely a demonstration of the infinite scope of God’s creative power. In comparison, the finest contrivances of man — a needle’s tip, a razor’s edge, a printed full stop — looked crude and clumsy under the microscope. Yet what excited Hooke and his contemporaries most of all was the thought that microscopes might uncover, not just the invisible structures of nature, but its hidden mechanisms as well. In previous ages, natural philosophers had attributed the causes of processes to invisible, occult forces and emanations — vague and insensible agencies. The new mechanistic philosophers of the 17th century argued that nature worked like a machine, filled with levers, hooks, mills, pins and other familiar devices too small to be seen. As Hooke put it: ‘Those effects of Bodies, which have been commonly attributed to Qualities, and those confess’d to be occult, are perform’d by the small Machines of Nature.’

He never quite found them — what the microscope revealed was more often unintelligible in these terms. But there was no shortage of other marvels.

If Micrographia had recorded life in the microscopic realm, it contained nothing that couldn’t be discerned, with effort, by the eye alone: ‘eels’ in vinegar and mites in cheese. Leeuwenhoek’s discoveries, reported in 1676 and verified by Hooke a year later, brought home the full force of a teeming, invisible microworld. The anxieties about scale and perspective that run through Swift’s Gulliver’s Travels (1726) make it clear how unsettling this was; recall Gulliver’s disgust at the gigantic bodies of the Brobdingnagians when seen close up: ‘Their skins appeared so coarse and uneven, so variously coloured when I saw them near, with a mole here and there as broad as a trencher, and hairs hanging from it thicker than pack-threads.’

In the 19th century, refinements to the design of the microscope allowed scientists to peer into the invisible world with unprecedented resolution. Yet there remained questions about what might be happening down there. In 1896 the pioneering British psychiatrist Henry Maudsley proclaimed that:

The universe, as it is within [man’s] experience, may be unlike the universe as it is within other living experience, and no more like the universe outside his experience, which he cannot think, than the universe of a mite is like his universe.

Maudsley’s protestation of ignorance was an attack on the complacent assumption held by some of his contemporaries that the invisible realms were peopled with beings like us. But this lack of knowledge could equally license the most exotic speculations. The beginnings of molecular science had suggested that life might have a minimal possible size. When the ‘indivisible’ atom began to display a finer-grained structure of subatomic particles, and light waves proved to have many unexpectedly fine oscillations in the form of X-rays, no one could rule out the possibility of an entire hierarchy of material existences on ever smaller scales.

Littleness has been a consistent theme in the folklore of demons and faeries

The physicist George Johnstone Stoney declared in 1891 that the physical universe is really an infinite series of worlds within worlds. The scientist Edmund Fournier d’Albe developed these ideas in Two New Worlds (1907), where he envisaged an ‘infra-world’ at a scale below that which microscopes could register, peopled, like Leeuwenhoek’s drop of water, with creatures that ‘eat, and fight, and love, and die, and whose span of life, to judge from their intense activity, is probably filled with as many events as our own’. The human body, he estimated, could play host to around 10 to the 40th power of these ‘infra-men’, experiencing joys and woes ‘without the slightest net effect on our own consciousness’.

As is often the case with scientific advance, the new and unfamiliar was popularly interpreted by reference to the old and prosaic. Littleness has been a consistent theme in the folklore of demons and faeries. Mischievous imps and fairies that interfere in domestic matters were a commonplace of folk tradition, and if these beings were not necessarily invisibly small, their diminutive stature enabled them to pass unseen. One might be tempted to imagine that, by the late 19th century, such beliefs persisted only in rural backwaters, but that would be to underestimate the grip of the invisible world on the imagination. Nowhere is this better illustrated than in the ‘demon’ of James Clerk Maxwell, perhaps the most profound physicist of the 19th century.

Maxwell’s idea was a response to the gloomy prediction of a ‘cosmic heat death’ of the universe. In 1851 William Thomson (later Lord Kelvin) pointed out that the second law of thermodynamics, which can be expressed as the condition that heat energy always flows from hot to cold, must eventually create a universe of uniform temperature, a universe from which no useful work can be extracted and in which nothing really happens.

A devout Christian, Maxwell could not accept that God would let this happen. He believed that the second law was statistical rather than fundamental: temperature gradients dissipated because it was far more likely that faster, ‘hotter’ molecules would mingle with slower ones, rather than by chance congregating into a ‘hot’ patch. But what if there were, as Maxwell put it in 1867, a ‘finite being’ small enough to ‘see’ each molecule and keep track of it, one who could open and shut a trapdoor in a wall that divided a gas-filled vessel? Such a being could let through fast-moving molecules in one direction so as to congregate the heat in one compartment, separating hot from cold and creating a temperature gradient that could be tapped to do work.

The nanobot was, in other words, a human avatar on an invisible scale

Maxwell didn’t intend his creature to be called a demon; that label was applied by Thomson, and Maxwell was not pleased. ‘Call him no more a demon but a valve,’ he grumbled — albeit a ‘valve’ with intelligence and autonomy. Or, as he put it elsewhere: ‘a doorkeeper, very intelligent and exceedingly quick’.

Several of his contemporaries took these ‘demons’ quite literally. Thomson himself took pains to stress that the demon was plausible, calling it ‘a being with no preternatural qualities, [which] differs from real animals only in extreme smallness and agility’. Maxwell’s friend, the Scottish physicist Peter Guthrie Tait, evidently believed they might exist, and he enlisted them for an extraordinary cause. In 1875, he and a fellow Scot named Balfour Stewart, an expert on the theory of heat, published a tract in which they attempted to show that ‘the presumed incompatibility of Science and Religion does not exist’. There must be, they wrote, ‘an invisible order of things which will remain and possess energy when the present system has passed away’. Tait and Stewart were aware of the apparent conflict between the Christian doctrine of the immortality of the soul and the second law of thermodynamics, which seemed to enforce an eventual universe of insensate stasis. Maxwell gave them a way out. ‘Clerk-Maxwell’s demons,’ they wrote, ‘could be made to restore energy even in the present universe without spending work’ — and as a result, ‘immortality is possible’.

Alas, modern studies have shown that Maxwell’s demon cannot evade the second law after all, since it would dissipate heat as part of the process of gathering information about molecular speeds. The conceit is now generally regarded as an amusing thought experiment: it is forgotten that, in Maxwell’s day, the notion of invisibly small demons going about their micro-business seemed plausible, even quite likely.

It should not be forgotten that the demonisation of invisible beings goes on in our own time, though now it is adapted to the fantasies of our age. And so viruses are ‘alien invaders’; we go to ‘war’ on ‘superbugs’ with super-powers, repelling them with ‘magic bullets’ as if they were werewolves. Children are taught that invisible ‘germs’ are the omnipresent enemy. Microbes are invoked, as imps and demons once were, to instil safe behaviour. It is a case, as the microbiologist Abraham Louis Baron declared in 1957, of ‘man against germs’. ‘We share the world with an incredible vast host of invisible things,’ he announced, but that wasn’t an expression of wonder so much as a warning. As the physician Robert Hessler wrote in his 1912 study of the hazards of dust: ‘It is the invisible we have to guard against.’

This fear of the malevolent designs of imperceptibly small entities became particularly evident in the early reception of nanotechnology. Among scientists, nanotechnology was a loosely defined collection of attempts to visualise and manipulate matter on scales ranging from ångströms (the size of atoms) to hundreds of nanometres (the size of small bacteria). In public discourse, however, it became dominated by a single, hypothetical entity: the nanobot. This, it was said, would be an autonomous device that could patrol the bloodstream for pathogenic invaders, or else construct materials and molecules, atom by atom. It was, in other words, a human avatar on an invisible scale.

Is the person who is gesticulating and talking out loud in the street communing with demons of the mind, or with a friend?

But what if nanobots ran amok, as robots (in fiction) are almost predestined to do? A rogue robot might be a menace, but it is a comprehensible one, a kind of superhuman being. A rogue nanobot, capable of replicating like bacteria and of pulling matter into its component particles, would be an unthinkable threat. Hidden from sight, it could reduce anything in seconds to a formless mass of atoms, which would then be reconstituted into replica nanobots: an amorphous ‘grey goo’. Michael Crichton exploited the terror of this imagery, crudely but effectively, in his novel Prey (2002).

If the grey goo idea is frightful, it is also familiar. Invisible powers have long been held capable of animating clay, creating the fearsome Golem, or of disintegrating and deliquescing matter and flesh (think now of the Ebola virus). What’s more, the nanobot connects with long-standing images of the exploration of new worlds, most notably the submarine Nautilus in which Captain Nemo explores the hidden deep sea in Jules Verne’s 20,000 Leagues Under the Sea (1870). Once again, it seems we must remake the invisible microworld in our own image before we can explore its promise and peril. This became most explicit in the 1966 film Fantastic Voyage, and its parodic 1987 remake, Innerspace, in which humans are shrunk to a scale that allows them to navigate through the human body.

The extreme miniaturisation that has its ultimate expression in nanotechnology has not yet given birth to an invisible nemesis. Indeed, it shows no sign of doing so. Instead, in conjunction with invisible rays such as Marconi’s ‘wireless’ emanations, it has created an age of technological invisibility, a world in which things happen with no mechanism in sight, even without our volition, via an omnipresent field of information. Items in stores speak to barriers and computers; miniaturised sensors control our cars and refine our household environment; libraries leap into our pockets. Dust, a metaphor for worthless matter while it was the smallest thing that could (just) be seen with the naked eye, has become ‘smart dust’, a nanotechnological promise of particles laced with invisible circuitry, programmed to self-assemble as we will them: to make a Golem, perhaps, rebranded now as a ‘reconfigurable robot’.

It has become a cliche that these advances would have seemed like magic in earlier times. Something that is acknowledged less frequently is how traditional reactions to invisibility might help us comprehend the cultural changes that have ensued. The boundaries between rationality and insanity can no longer be policed in behavioural terms. Is the person who is gesticulating and talking out loud in the street communing with demons of the mind, or with a friend? Is the person fretting over the invisible threats of nearby radio masts succumbing to some modern version of the mal aria theory of contagion, or do they have a point? We entrust our digital secrets to the intangible Cloud, assuming that this nebulous entity can be summoned to regurgitate them at will. With invisibly small technology harnessed to the invisible ether, we have animated the world.

Popular conversations

Ask your question

Topics: Biology History of Science History of Technology

Card spider dances for his life main


Dance or die! A male spider must impress a female with his moves, or be eaten

4 minutes

Card essay 525371733


Better babies

The long and peculiar history of the designer human, from Plato’s citizen breeders to Nobel sperm banks and beyond

by Nathaniel Comfort

Card why cant we walk straight main 2


Why can’t blindfolded people walk in a straight line? It’s a scientific mystery

4 minutes

Card final scf10040


Made to order

Parents already put their children under intense pressure to compete in the world. Will gene editing make it worse?

by Erik Parens