A Financial Times, Sunday Times, and Telegraph Best Science Book of the Year
What is life? For generations, scientists have struggled to make sense of this fundamental question, for life really does look like magic: even a humble bacterium accomplishes things so dazzling that no human engineer can match it. Huge advances in molecular biology over the past few decades have served only to deepen the mystery.
In this penetrating and wide-ranging book, world-renowned physicist and science communicator Paul Davies searches for answers in a field so new and fast-moving that it lacks a name; it is a domain where biology, computing, logic, chemistry, quantum physics, and nanotechnology intersect. At the heart of these diverse fields, Davies explains, is the concept of information: a quantity which has the power to unify biology with physics, transform technology and medicine, and force us to fundamentally reconsider what it means to be alive—even illuminating the age-old question of whether we are alone in the universe.
From life’s murky origins to the microscopic engines that run the cells of our bodies, The Demon in the Machine journeys across an astounding landscape of cutting-edge science. Weaving together cancer and consciousness, two-headed worms and bird navigation, Davies reveals how biological organisms garner and process information to conjure order out of chaos, opening a window onto the secret of life itself.
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What is Life?
In February 1943 the physicist Erwin Schrödinger delivered a series of lectures at Trinity College in Dublin called What is Life? Schrödinger was a celebrity, a Nobel prizewinner, and world famous as an architect of quantum mechanics, the most successful scientific theory ever. It had already explained, within a few years of its formulation in the 1920s, the structure of atoms, the properties of atomic nuclei, radioactivity, the behaviour of subatomic particles, chemical bonds, the thermal and electrical properties of solids and the stability of stars.
Schrödinger's own contribution had begun in 1926 with a new equation that still bears his name, describing how electrons and other subatomic particles move and interact. The decade or so that followed was a golden age for physics, with major advances on almost every front, from the discovery of antimatter and the expanding universe to the prediction of neutrinos and black holes, due in large part to the power of quantum mechanics to explain the atomic and subatomic world. But those heady days came to an abrupt end when in 1939 the world was plunged into war. Many scientists fled Nazi Europe for Britain or the United States to assist the Allied war effort. Schrödinger joined the exodus, leaving his native Austria after the Nazi takeover in 1938, but he decided to make a home in neutral Ireland. Ireland's president, Éamon de Valera, himself a physicist, founded a new Institute for Advanced Studies in 1940 in Dublin. It was de Valera himself who invited Schrödinger to Ireland, where he stayed for sixteen years, accompanied by both wife and mistress living under the same roof.
In the 1940s biology lagged far behind physics. The details of life's basic processes remained largely mysterious. Moreover, the very nature of life seemed to defy one of physics' fundamental laws – the so-called second law of thermodynamics – according to which there is a universal tendency towards degeneration and disorder. In his Dublin lectures Schrödinger set out the problem as he saw it: 'how can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?' In other words, can the baffling properties of living organisms ultimately be reduced to atomic physics, or is something else going on? Schrödinger put his finger on the key issue. For life to generate order out of disorder and buck the second law of thermodynamics, there had to be a molecular entity that somehow encoded the instructions for building an organism, at once complex enough to embed a vast quantity of information and stable enough to withstand the degrading effects of thermodynamics. We now know that this entity is DNA.
In the wake of Schrödinger's penetrating insights, which were published in book form the next year, the field of molecular biology exploded. The elucidation of the structure of DNA, the cracking of the genetic code and the merging of genetics with the theory of evolution followed swiftly. So rapid and so sweeping were the successes of molecular biology that most scientists adopted a strongly reductionist view: it did indeed seem that the astonishing properties of living matter could ultimately be explained solely in terms of the physics of atoms and molecules, without the need for anything fundamentally new. Schrödinger himself, however, was less sanguine: '... living matter, while not eluding the "laws of physics" as established up to date, is likely to involve "other laws of physics" hitherto unknown ...' he wrote. In this he was not alone. Fellow architects of quantum mechanics such as Niels Bohr and Werner Heisenberg also felt that living matter might require new physics.
Strong reductionism still prevails in biology. The orthodox view remains that known physics alone is all that is needed to explain life, even if most of the details haven't been entirely worked out. I disagree. Like Schrödinger, I think living organisms manifest deep new physical principles, and that we are on the threshold of uncovering and harnessing those principles. What is different this time, and why it has taken so many decades to discover the real secret of life, is that the new physics is not simply a matter of an additional type of force – a 'life force' – but something altogether more subtle, something that interweaves matter and information, wholes and parts, simplicity and complexity.
That 'something' is the central theme of this book.
GOODBYE LIFE FORCE
Throughout history it was recognized that living organisms possess strange powers, such as the ability to move autonomously, to rearrange their environment and to reproduce. The philosopher Aristotle attempted to capture this elusive otherness with a concept known as teleology – derived from the Greek word telos, meaning 'goal' or 'end'. Aristotle observed that organisms seem to behave purposefully according to some pre-arranged plan or project, their activities being directed or pulled towards a final state, whether it is seizing food, building a nest or procreating through sex.
In the early scientific era the view persisted that living things were made of a type of magic matter, or at least normal matter infused with an added ingredient. It was a point of view known as vitalism. Just what that extra essence might be was left vague; suggestions included air (the breath of life), heat, electricity, or something mystical like the soul. Whatever it might be, the assumption that a special type of 'life force' or ethereal energy served to animate matter was widespread into the nineteenth century.
With improvements in scientific techniques such as the use of powerful microscopes, biologists found more and more surprises that seemed to demand a life force. One major puzzle concerned embryo development. Who could not be astonished by the way that a single fertilized egg cell, too small to see with the unaided eye, can grow into a baby? What guides the embryo's complex organization? How can it unfold so reliably to produce such an exquisitely arranged outcome? The German embryologist Hans Dreisch was particularly struck by a series of experiments he performed in 1885. Dreisch tried mutilating the embryos of sea urchins – a favourite victim among biologists – only to find they somehow recovered and developed normally. He discovered it was even possible to disaggregate the developing ball of cells at the four-cell stage and grow each individual cell into a complete sea urchin. Results such as these gave Dreisch the impression that the embryonic cells possessed some 'idea in advance' of the final shape they intended to create and cleverly compensated for the experimenter's meddling. It was as if some invisible hand supervised their growth and development, effecting 'midcourse corrections' if necessary. To Dreisch, these facts constituted strong evidence for some form of vital essence, which he termed entelechy, meaning 'complete, perfect, final form' in Greek, an idea closely related to Aristotle's notion of teleology.
But trouble was brewing for the life force. For such a force actually to accomplish something it must – like all forces – be able to move matter. And at first sight, organisms do indeed seem to be self-propelled, to possess some inner source of motive power. But exerting any kind of force involves expending energy. So, if the 'life force' is real, then the transfer of energy should be measurable. The physicist Hermann von Helmholtz investigated this very issue intensively in the 1840s. In a series of experiments he applied pulses of electricity to muscles extracted from frogs, which caused them to twitch, and carefully measured the minute changes in temperature that accompanied the movement. Helmholtz concluded that it was chemical energy stored in the muscles that, triggered by the jolt of electricity, became converted into the mechanical energy of twitching which, in turn, degraded into heat. The energy books balanced nicely without any evidence of the need for additional vital forces to be deployed. Yet it took several more decades for vitalism to fade away completely.
But even without a life force, it's hard to shake the impression that there is something special about living matter. The question is, what?
I became fascinated with this conundrum after reading Schrödinger's book What is Life? as a student. At one level the answer is straightforward: living organisms reproduce, metabolize, respond to stimuli, and so forth. However, merely listing the properties of life does not amount to an explanation, which is what Schrödinger sought. As much as I was inspired by Schrödinger's book, I found his account frustratingly incomplete. It was clear to me that life must involve more than just the physics of atoms and molecules. Although Schrödinger suggested that some sort of new physics might be at play, he didn't say what. Subsequent advances in molecular biology and biophysics gave few clues. But very recently the outline of a solution has emerged, and it comes from a totally novel direction.
LIFE SPRINGS SURPRISES
'Base metals can be transmuted into gold by stars, and by intelligent beings who understand the processes that power stars, and by nothing else in the universe.'
– David Deutsch
Understanding the answer to Schrödinger's question 'What is life?' means abandoning the traditional list of properties that biologists reel off, and beginning to think about the living state in a totally new way. Ask the question, 'How would the world be different if there were no life?' It is common knowledge that our planet has been shaped in part by biology: the build-up of oxygen in the atmosphere, the formation of mineral deposits, the worldwide effects of human technology. Many non-living processes also reshape the planet – volcanic eruptions, asteroid impacts, glaciation. The key distinction is that life brings about processes that are not only unlikely but impossible in any other way. What else can fly halfway round the world with pinpoint precision (the Arctic tern), convert sunlight into electrical energy with 90 per cent efficiency (leaves) or build complex networks of underground tunnels (termites)?
Of course, human technology – a product of life – can do these things too, and more. To illustrate: for 4.5 billion years, since the solar system formed, Earth has accumulated material – the technical term is 'accretion' – from asteroid and comet impacts. Objects of various sizes, from hundreds of kilometres across to tiny meteoric grains, have rained down throughout our planet's history. Most people know about the dinosaur-destroying comet that slammed into what is now Mexico 65 million years ago, but that was just one instance. Aeons of bombardment means that our planet is slightly heavier today than it was in the past. Since 1958, however, 'anti-accretion' has occurred. Without any sort of geological catastrophe, a large swarm of objects has gone the other way – up from Earth into space, some to travel to the moon and planets, others to journey into the void for good; most of them have ended up orbiting Earth. This state of affairs would be impossible based purely on the laws of mechanics and planetary evolution. It is readily explained, however, by human rocket technology.
Another example. When the solar system formed, a small fraction of its initial chemical inventory included the element plutonium. Because the longest-lived isotope of plutonium has a half-life of about 81 million years, virtually all the primordial plutonium has now decayed. But in 1940 plutonium reappeared on Earth as a result of experiments in nuclear physics; there are now estimated to be a thousand tonnes of it. Without life, the sudden rise of terrestrial plutonium would be utterly inexplicable. There is no plausible non-living pathway from a 4.5-billion-year-old dead planet to one with deposits of plutonium.
Life does not merely effect these changes opportunistically, it diversifies and adapts, invading new niches and inventing ingenious mechanisms to make a living, sometimes in extraordinary ways. Three kilometres below ground in South Africa's Mponeng gold mine colonies of exotic bacteria nestle in the microscopic pores of the torrid, gold-bearing rocks, isolated from the rest of our planet's biosphere. There is no light to sustain them, no organic raw material to eat. The source of the microbes' precarious existence is, astonishingly, radioactivity. Normally deadly to life, nuclear radiation emanating from the rocks provides the subterranean denizens with enough energy by splitting water into oxygen and hydrogen. The bacteria, known as Desulforudis audaxviator, have evolved mechanisms to exploit the chemical by-products of radiation, making biomass by combining the hydrogen with carbon dioxide dissolved in the scalding water that suffuses the rocks.
Eight thousand kilometres away, in the desiccated heart of the Atacama Desert in Chile, the fierce sun rises over a unique landscape. As far as the eye can see there is only sand and rock, unrelieved by signs of life. No birds, insects or plants embellish the view. Nothing scrambles in the dust, no green patches betray the presence of even simple algae. All known life needs liquid water, and it virtually never rains in this region of the Atacama, making it the driest, and deadest, place on the Earth's surface.
The core of the Atacama is Earth's closest analogue to the surface of Mars, so NASA has a field station there to test theories about Martian soil. The scientists went originally to study the outer limits of life – they like to say they are looking for death, not life – but what they found instead was startling. Scattered amid the outcrops of desert rock are weird, sand-encrusted shapes, pillars rising to a height of a metre or so, rounded and knobbed, resembling a riot of sculptures that might have been designed by Salvador Dalí. The mounds are in fact made of salt, remnants of an ancient lake long since evaporated. And inside the pillars, literally entombed in salt, are living microbes that eke out a desperate existence against all the odds. These very different weird organisms, named Chroococcidiopsis, get their energy not from radioactivity but, more conventionally, from photosynthesis; the strong desert sunlight penetrates their translucent dwellings. But there remains the question of water. This part of the Atacama Desert lies about a hundred kilometres inland from the cold Pacific Ocean, from which it is separated by a mountain range. Under the right conditions, fingers of sea mist meander through the mountain passes at night when the temperature plunges. The dank air infuses water molecules into the salt matrix. The water doesn't form liquid droplets; rather, the salt becomes damp and sticky, a phenomenon well known to those readers who live in wet climes and are familiar with obstinate salt cellars. The absorption of water vapour into salt is called deliquescence, and it serves well enough – just – to keep the microbes happy for a while before the morning sun bakes the salt dry.
Desulforudis audaxviator and Chroococcidiopsis are two examples illustrating the extraordinary ability of living organisms to survive in dire circumstances. Other microbes are known to withstand extremes of cold or heat, salinity and metal contamination, and acidity fierce enough to burn human flesh. The discovery of this menagerie of resilient microbes living on the edge (collectively called extremophiles) overturned a long-standing belief that life could flourish only within narrow margins of temperature, pressure, acidity, and so forth. But life's profound ability to create new physical and chemical pathways and to tap into a range of unlikely energy sources illustrates how, once life gets going, it has the potential to spread far beyond its original habitat and trigger unexpected transformations. In the far future, humans or their machine descendants may reconfigure the entire solar system or even the galaxy. Other forms of life elsewhere in the universe could already be doing something similar, or may eventually do so. Now that life has been unleashed into the universe, it has within it the potential to bring about changes of literally cosmic significance.
THE VEXING PROBLEM OF THE LIFE METER
There is a dictum in science that if something is real, then we ought to be able to measure it (and perhaps even tax it). Can we measure life? Or 'degree of aliveness'? That may seem an abstract question, but it recently assumed a certain immediacy. In 1997 the US and European space agencies collaborated to send a spacecraft named Cassini to Saturn and its moons. Great interest was focused on the moon Titan, the largest in the solar system. Titan was discovered by Christiaan Huygens in 1655 and has long been a curiosity to astronomers, not only because of its size but because it is covered in clouds. Until the Cassini mission, what lay beneath was, literally, shrouded in mystery. The Cassini spacecraft conveyed a small probe, fittingly called Huygens, which was dropped through Titan's clouds to land safely on the moon's surface. Huygens revealed a landscape featuring oceans and beaches, but the oceans are made of liquid ethane and methane and the rocks are made of water ice. Titan is very cold, with an average temperature of -180°C.(Continues…)
Excerpted from "The Demon in the Machine"
Copyright © 2019 Paul Davies.
Excerpted by permission of The University of Chicago Press.
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Table of Contents
1. What is Life?
2. Enter the Demon
3. The Logic of Life
4. Darwinism 2.0
5. Spooky Life and Quantum Demons
6. Almost a Miracle
7. The Ghost in the Machine