Our imaginations are forlornly under-equipped to cope with distances outside the narrow middle range of the ancestrally familiar. We try to visualize an electron as a tiny ball, in orbit around a larger cluster of balls representing protons and neutrons. That isn't what it is like at all. Electrons are not like little balls. They are not like anything we recognize. It isn't clear that 'like' even means anything when we try to fly too close to reality's further horizons. Our imaginations are not yet tooled-up to penetrate the neighbourhood of the quantum. Nothing at that scale behaves in the way matter - as we are evolved to think - ought to behave. Nor can we cope with the behaviour of objects that move at some appreciable fraction of the speed of light. Common sense lets us down, because common sense evolved in a world where nothing moves very fast, and nothing is very small or very large.
At the end of a famous essay on 'Possible Worlds', the great biologist J. B. S. Haldane wrote, 'Now, my own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose ... I suspect that there are more things in heaven and earth than are dreamed of, or can be dreamed of, in any philosophy.' By the way, I am intrigued by the suggestion that the famous Hamlet speech invoked by Haldane is conventionally misspoken. The normal stress is on 'your':
There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.
Indeed, the line is often plonkingly quoted with the implication that Horatio stands for shallow rationalists and sceptics everywhere. But some scholars place the stress on 'philosophy', with 'your' almost vanishing: '. . . than are dreamt of inya philosophy.' The difference doesn't really matter for present purposes, except that the second interpretation already takes care of Haldane's 'any' philosophy.
The dedicatee of this book made a living from the strangeness of science, pushing it to the point of comedy. The following is taken from the same extempore speech in Cambridge in 1998 from which I have already quoted: 'The fact that we live at the bottom of a deep gravity well, on the surface of a gas-covered planet going around a nuclear fireball ninety million miles away and think this to be normal is obviously some indication of how skewed our perspective tends to be.' Where other science-fiction writers played on the odd-ness of science to arouse our sense of the mysterious, Douglas Adams used it to make us laugh (those who have read The Hitchhiker's Guide to the Galaxy might think of the 'infinite improbability drive', for instance). Laughter is arguably the best response to some of the stranger paradoxes of modern physics. The alternative, I sometimes think, is to cry.
Quantum mechanics, that rarefied pinnacle of twentieth-century scientific achievement, makes brilliantly successful predictions about the real world. Richard Feynman compared its precision to predicting a distance as great as the width of North America to an accuracy of one human hair's breadth. This predictive success seems to mean that quantum theory has got to be true in some sense; as true as anything we know, even including the most down-to-earth common-sense facts. Yet the assumptions that quantum theory needs to make, in order to deliver those predictions, are so mysterious that even the great Feynman himself was moved to remark (there are various versions of this quotation, of which the following seems to me the neatest): 'If you think you understand quantum theory . . . you don't understand quantum theory.'*
* A similar remark is attributed to Niels Bohr: 'Anyone who is not shocked by quantum theory has not understood it.'
Quantum theory is so queer that physicists resort to one or another paradoxical 'interpretation' of it. Resort is the right word. David Deutsch, in The Fabric of Reality, embraces the 'many worlds' interpretation of quantum theory, perhaps because the worst that you can say of it is that it is preposterously wasteful. It postulates a vast and rapidly growing number of universes, existing in parallel and mutually undetectable except through the narrow porthole of quantum-mechanical experiments. In some of these universes I am already dead. In a small minority of them, you have a green moustache. And so on.
The alternative 'Copenhagen interpretation' is equally preposterous - not wasteful, just shatteringly paradoxical. Erwin Schrodinger satirized it with his parable of the cat. Schrodinger's cat is shut up in a box with a killing mechanism triggered by a quantum-mechanical event. Before we open the lid of the box, we don't know whether the cat is dead. Common sense tells us that, nevertheless, the cat must be either alive or dead inside the box. The Copenhagen interpretation contradicts common sense: all that exists before we open the box is a probability. As soon as we open the box, the wave function collapses and we are left with the single event: the cat is dead, or the cat is alive. Until we opened the box, it was neither dead nor alive.
The 'many worlds' interpretation of the same events is that in some universes the cat is dead; in other universes the cat is alive. Neither interpretation satisfies human common sense or intuition. The more macho physicists don't care. What matters is that the mathematics work, and the predictions are experimentally fulfilled. Most of us are too wimpish to follow them. We seem to need some sort of visualization of what is 'really' going on. I understand, by the way, that Schrodinger originally proposed his cat thought-experiment in order to expose what he saw as the absurdity of the Copenhagen interpretation.
The biologist Lewis Wolpert believes that the queerness of modern physics is just the tip of the iceberg. Science in general, as opposed to technology, does violence to common sense.156 Here's a favourite example: every time you drink a glass of water, the odds are good that you will imbibe at least one molecule that passed through the bladder of Oliver Cromwell. It's just elementary probability theory. The number of molecules per glassful is hugely greater than the number of glassfuls in the world. So every time we have a full glass, we are looking at a rather high proportion of the molecules of water that exist in the world. There is, of course, nothing special about Cromwell, or bladders. Haven't you just breathed in a nitrogen atom that was once breathed out by the third iguanodon to the left of the tall cycad tree? Aren't you glad to be alive in a world where not only is such a conjecture possible but you are privileged to understand why? And publicly explain it to somebody else, not as your opinion or belief but as something that they, when they have understood your reasoning, will feel compelled to accept? Maybe this is an aspect of what Carl Sagan meant when he explained his motive in writing The Demon-Haunted World: Science as a Candle in the Dark: 'Not explaining science seems to me perverse. When you're in love, you want to tell the world. This book is a personal statement, reflecting my lifelong love affair with science.'
The evolution of complex life, indeed its very existence in a universe obeying physical laws, is wonderfully surprising - or would be but for the fact that surprise is an emotion that can exist only in a brain which is the product of that very surprising process. There is an anthropic sense, then, in which our existence should not be surprising. I'd like to think that I speak for my fellow humans in insisting, nevertheless, that it is desperately surprising.
Think about it. On one planet, and possibly only one planet in the entire universe, molecules that would normally make nothing more complicated than a chunk of rock, gather themselves together into chunks of rock-sized matter of such staggering complexity that they are capable of running, jumping, swimming, flying, seeing, hearing, capturing and eating other such animated chunks of complexity; capable in some cases of thinking and feeling, and falling in love with yet other chunks of complex matter. We now understand essentially how the trick is done, but only since 1859. Before 1859 it would have seemed very very odd indeed. Now, thanks to Darwin, it is merely very odd. Darwin seized the window of the burka and wrenched it open, letting in a flood of understanding whose dazzling novelty, and power to uplift the human spirit, perhaps had no precedent - unless it was the Copernican realization that the Earth was not the centre of the universe.
'Tell me,' the great twentieth-century philosopher Ludwig Wittgenstein once asked a friend, 'why do people always say it was natural
for man to assume that the sun went round the Earth rather than that the Earth was rotating?' His friend replied, 'Well, obviously because it just looks as though the Sun is going round the Earth.' Wittgenstein responded, 'Well, what would it have looked like if it had looked as though the Earth was rotating?' I sometimes quote this remark of Wittgenstein in lectures, expecting the audience to laugh. Instead, they seem stunned into silence.
In the limited world in which our brains evolved, small objects are more likely to move than large ones, which are seen as the background to movement. As the world rotates, objects that seem large because they are near - mountains, trees and buildings, the ground itself - all move in exact synchrony with each other and with the observer, relative to heavenly bodies such as the sun and stars. Our evolved brains project an illusion of movement onto them rather than the mountains and trees in the foreground.
I now want to pursue the point mentioned above, that the way we see the world, and the reason why we find some things intuitively easy to grasp and others hard, is that our brains are themselves evolved organs: on-board computers, evolved to help us survive in a world - I shall use the name Middle World - where the objects that mattered to our survival were neither very large nor very small; a world where things either stood still or moved slowly compared with the speed of light; and where the very improbable could safely be treated as impossible. Our mental burka window is narrow because it didn't need to be any wider in order to assist our ancestors to survive.
Science has taught us, against all evolved intuition, that apparently solid things like crystals and rocks are really composed almost entirely of empty space. The familiar illustration represents the nucleus of an atom as a fly in the middle of a sports stadium. The next atom is right outside the stadium. The hardest, solidest, densest rock, then, is 'really' almost entirely empty space, broken only by tiny particles so far apart that they shouldn't count. So why do rocks look and feel solid and hard and impenetrable?
I won't try to imagine how Wittgenstein might have answered that question. But, as an evolutionary biologist, I would answer it like this. Our brains have evolved to help our bodies find their way around the world on the scale at which those bodies operate. We never evolved to navigate the world of atoms. If we had, our brains probably would perceive rocks as full of empty space. Rocks feel hard and impenetrable to our hands because our hands can't penetrate them. The reason they can't penetrate them is unconnected with the sizes and separations of the particles that constitute matter. Instead, it has to do with the force fields that are associated with those widely spaced particles in 'solid' matter. It is useful for our brains to construct notions like solidity and impenetrability, because such notions help us to navigate our bodies through a world in which objects - which we call solid - cannot occupy the same space as each other.
A little comic relief at this point - from The Men who Stare at Goats by Jon Ronson:
This is a true story. It is the summer of 1983. Major General Albert Stubblebine III is sitting behind his desk in Arlington, Virginia, and he is staring at his wall, upon which hang his numerous military awards. They detail a long and distinguished career. He is the United States Army's chief of intelligence, with sixteen thousand soldiers under his command ... He looks past his awards to the wall itself. There is something he feels he must do even though the thought of it frightens him. He thinks about the choice he has to make. He can stay in his office or he can go into the next office. That is his choice. And he has made it. He is going into the next office . . . He stands up, moves out from behind his desk, and begins to walk. I mean, he thinks, what is the atom mostly made up of anyway? Space! He quickens his pace. What am I mostly made of? He thinks. Atoms! He is almost at a jog now. What is the wall mostly made up of? He thinks. Atoms! All I have to do is merge the spaces. . . . Then General Stubblebine bangs his nose hard on the wall of his office. Damn, he thinks. General Stubblebine is confounded by his continual failure to walk through his wall. What's wrong with him that he can't do it? Maybe there is simply too much in his in-tray for him to give it the requisite level of concentration. There is no doubt in his mind that the ability to pass through objects will one day be a common tool in the intelligence-gathering arsenal. And when that happens, well, is it too naive to believe it would herald the dawning of a world without war? Who would want to screw around with an army that could do that?
General Stubblebine is appropriately described as an 'out of the box thinker' on the website of the organization which, in retirement, he now runs with his wife.
Having evolved in Middle World, we find it intuitively easy to grasp ideas like: 'When a major general moves, at the sort of medium velocity at which major generals and other Middle World objects do move, and hits another solid Middle World object like a wall, his progress is painfully arrested.' Our brains are not equipped to imagine what it would be like to be a neutrino passing through a wall, in the vast interstices of which that wall 'really' consists. Nor can our understanding cope with what happens when things move at close to the speed of light.
Unaided human intuition, evolved and schooled in Middle World, even finds it hard to believe Galileo when he tells us that a cannon ball and a feather, given no air friction, would hit the ground at the same instant when dropped from a leaning tower. That is because, in Middle World, air friction is always there. If we had evolved in a vacuum, we would expect a feather and a cannonball to hit the ground simultaneously. We are evolved denizens of Middle World, and that limits what we are capable of imagining. The narrow window of our burka permits us, unless we are especially gifted or peculiarly well educated, to see only Middle World.
There is a sense in which we animals have to survive not just in Middle World but in the micro-world of atoms and electrons too. The very nerve impulses with which we do our thinking and our imagining depend upon activities in Micro World. But no action that our wild ancestors ever had to perform, no decision that they ever had to take, would have been assisted by an understanding of Micro World. If we were bacteria, constantly buffeted by thermal movements of molecules, it would be different. But we Middle Worlders are too cumbersomely massive to notice Brownian motion. Similarly, our lives are dominated by gravity but are almost oblivious to the delicate force of surface tension. A small insect would reverse that priority and would find surface tension anything but delicate.
Steve Grand, in Creation: Life and How to Make It, is almost scathing about our preoccupation with matter itself. We have this tendency to think that only solid, material 'things' are 'really' things at all. 'Waves' of electromagnetic fluctuation in a vacuum seem 'unreal'. Victorians thought that waves had to be waves 'in' some material medium. No such medium was known, so they invented one and named it the luminiferous ether. But we find 'real' matter comfortable to our understanding only because our ancestors evolved to survive in Middle World, where matter is a useful construct.
On the other hand, even we Middle Worlders can see that a whirlpool is a 'thing' with something like the reality of a rock, even though the matter in the whirlpool is constantly changing. In a desert plain in Tanzania, in the shadow of 01 Donyo Lengai, sacred volcano of the Masai, there is a large dune made of ash from an eruption in 1969. It is carved into shape by the wind. But the beautiful thing is that it moves bodily. It is what is technically known as a barchan (pronounced bahkahn). The entire dune walks across the desert in a westerly direction at a speed of about 17 metres per year. It retains its crescent shape and creeps along in the direction of the horns. The wind blows sand up the shallower slope. Then, as each sand grain hits the top of the ridge, it cascades down the steeper slope on the inside of the crescent.
Actually, even a barchan is more of a 'thing' than a wave. A wave seems to move horizontally across the open sea, but the molecules of water move vertically. Similarly, sound waves may travel from speaker to listener, but molecules of air don't: that would be a wind, not a sound. Steve Grand points out that you and I are more like waves than perman
ent 'things'. He invites his reader to think . . .
... of an experience from your childhood. Something you remember clearly, something you can see, feel, maybe even smell, as if you were really there. After all, you really were there at the time, weren't you? How else would you remember it? But here is the bombshell: you weren't there. Not a single atom that is in your body today was there when that event took place . . . Matter flows from place to place and momentarily comes together to be you. Whatever you are, therefore, you are not the stuff of which you are made. If that doesn't make the hair stand up on the back of your neck, read it again until it does, because it is important.
'Really' isn't a word we should use with simple confidence. If a neutrino had a brain which had evolved in neutrino-sized ancestors, it would say that rocks 'really' do consist mostly of empty space. We have brains that evolved in medium-sized ancestors, who couldn't walk through rocks, so our 'really' is a 'really' in which rocks are solid. 'Really', for an animal, is whatever its brain needs it to be, in order to assist its survival. And because different species live in such different worlds, there will be a troubling variety of 'reallys'.
What we see of the real world is not the unvarnished real world but a model of the real world, regulated and adjusted by sense data - a model that is constructed so that it is useful for dealing with the real world. The nature of that model depends on the kind of animal we are. A flying animal needs a different kind of world model from a walking, a climbing or a swimming animal. Predators need a different kind of model from prey, even though their worlds necessarily overlap. A monkey's brain must have software capable of simulating a three-dimensional maze of branches and trunks. A water boatman's brain doesn't need 3D software, since it lives on the surface of the pond in an Edwin Abbott Flatland. A mole's software for constructing models of the world will be customized for underground use. A naked mole rat probably has world-representing software similar to a mole's. But a squirrel, although it is a rodent like the mole rat, probably has world-rendering software much more like a monkey's.