10
Quantum biology: life on the edge of a storm

“WEIRD” is the adjective most frequently used to describe the field of quantum mechanics. And it is weird. Any theory that allows objects to pass through impenetrable barriers, to be in two places at once or to possess “spooky connections” cannot be described as ordinary. But in fact its mathematical framework is absolutely logical and consistent, and accurately describes the way the world is at the level of fundamental particles and forces. Quantum mechanics is thus the bedrock of physical reality. Discrete energy levels, wave–particle duality, coherence, entanglement and tunneling aren’t just interesting ideas relevant only to scientists working within rarefied physics laboratories. They are as real and as normal as Grandma’s apple pie, and indeed are going on inside Grandma’s apple pie. Quantum mechanics is normal. It is the world it describes that is weird.

But, as we have discovered, most of the counterintuitive features of matter at the quantum scale are washed away in the turbulent thermodynamic interiors of big objects by the process we call decoherence, leaving just our familiar classical world. So we can view physical reality as consisting of three levels (figure 10.1). On the surface are the macroscopic, everyday objects such as footballs, trains and planets, whose overall behavior adheres to Newton’s mechanical laws of motion involving such familiar concepts as speed, acceleration, momentum and forces. The middle layer is the thermodynamic layer that describes the behavior of liquids and gases. Here, the same classical Newtonian rules apply; but, as Schrödinger pointed out and as we described in chapter 2, these underlying thermodynamic laws, which describe for example how a gas expands when heated or how a steam engine drives trains up hillsides, are based on the “order from disorder” averaging of the disorderly billiard-ball-like jostling of trillions of atoms and molecules. The third and deepest level is the bedrock of reality: the quantum world. Here is where the behavior of the atoms and molecules and the particles from which they are made obeys the precise and orderly rules of quantum, not classical, mechanics. However, most of the weird quantum stuff is generally invisible to us. It is only when we carefully observe individual molecules, as for example in the double-slit experiment, that we see the deeper, quantum laws. The behavior they describe appears unfamiliar to us because we normally see reality through a decoherence filter that strips out all the weirdness from bigger objects.

Figure 10.1: The three strata of reality. The top layer is the visible world, filled with objects such as falling apples, cannonballs, steam trains and airplanes, whose motions are described by Newtonian mechanics. Lying beneath is the thermodynamic layer of billiard-ball-like particles whose motion is almost entirely random. This layer is responsible for generating the “order from disorder” laws that govern the behavior of objects such as steam engines. The next layer down is the layer of fundamental particles ruled by orderly quantum laws. The visible features of most of the objects that we see around us appear to be rooted in either the Newtonian or thermodynamic layers but living organisms have roots that penetrate right down to the quantum bedrock of reality.

Most living organisms are relatively large objects. Like trains, footballs and cannonballs, their overall motion adheres pretty well to Newtonian laws: a man fired out of a cannon has a similar trajectory as that of a cannonball. At a deeper level, the physiology of tissues and cells is also well described by the thermodynamic laws: the expansion and contraction of a lung is not so different from the expansion and contraction of a balloon. So at first glance you would tend to assume, and most scientists have assumed, that the quantum behavior similarly gets washed away in robins, fish, dinosaurs, apple trees, butterflies and us, just as it does in other classical objects. But we have seen that this is not always true for life; its roots reach down from the Newtonian surface through the turbulent thermodynamic waters to penetrate the quantum bedrock, allowing life to harness coherence, superposition, tunneling or entanglement (figure 10.1). The question we want to address in this final chapter is: How?

We have already explored part of the answer. Erwin Schrödinger pointed out more than sixty years ago that life is different from the inorganic world because it is structured and orderly even at a molecular level. This order all the way down endows life with a kind of rigid leverage that connects the molecular to the macroscopic, such that quantum events taking place within individual biomolecules can have consequences for an entire organism: the kind of amplification from the quantum to the macroscopic asserted by that other quantum pioneer, Pascual Jordan.

Of course, when Schrödinger and Jordan were writing about biology nobody knew what a gene was made of, or how enzymes or photosynthesis worked. But half a century of intensive molecular biology research has provided us with an extraordinarily detailed map of the structure of biomolecules at the level of individual atoms in DNA or proteins. And, as we have discovered, the quantum pioneers’ prescient insights have, rather belatedly, been vindicated. Photosystems, enzymes, respiratory chains and genes are structured right down to the position of individual particles, and their quantum motions do indeed make a difference to the respiration that keeps us alive, the enzymes that build our bodies or the photosynthesis that makes nearly all the biomass on our planet.

And yet many questions remain, principally concerning how life manages to maintain quantum coherence in the warm, wet sea of biomolecules within a living cell. Proteins or DNA are not steel-built machines with rigid parts, like the instruments used to detect quantum effects in physics laboratories; they are squishy, flexible structures that are constantly subjected to their own thermal vibrations as well as being continuously battered by the bumping of surrounding molecular billiard balls, a constant barrage of molecular noise.*1 These random vibrations and collisions would be expected to shatter the delicate arrangement of atoms and molecules those particles need to maintain their quantum behavior. How this coherence is preserved in biology remains a puzzle; but, as we will discover, it is one that is beginning to be unraveled to reveal fascinating insights into how life works; insights that might even be exploited to drive the quantum technologies of the future.

Good, good, good, good vibrations (bop bop)

Few popular science books require revision during their writing; but in this final chapter we will describe results that are emerging right now. Indeed, the science of quantum biology is moving so fast, on so many different fronts, that this book will inevitably be a little out of date by the time it is published. The biggest surprises to emerge from recent studies are new insights into how life copes with molecular vibrations or noise.

Some of the most exciting new results in this area are emerging from further studies of photosynthesis. You will remember from chapter 4 that microbes and plant leaves are packed full of chloroplasts filled with forests of chlorophyll pigment molecules, and that the first step in photosynthesis involves the capture of a photon of light by a pigment molecule and its conversion to an oscillating exciton that gets whisked through the chlorophyll forest to the reaction center. You will also remember that the signature of coherence, quantum beating, was detected in this energy transport process—evidence that its near 100 percent efficiency is thanks to excitons quantum walking their way to the reaction center. But how excitons maintain their coherent wave-like behavior while strolling through the molecularly noisy environment of a living cell has, until recently, been a puzzle. We have now discovered that the answer seems to be that living systems don’t try to avoid molecular vibration; instead, they dance to its beat.

In chapter 4 we envisaged quantum coherence in photosynthesis as a kind of molecular version of an orchestra being “in tune” and “in time,” with all the coherent pigment molecules playing to the same beat. But the problem the system has to overcome is that the inside of the cell is very noisy. This molecular orchestra is playing not in a quiet concert hall, but in something more like a busy city center, amid a cacophony of molecular noise that disturbs each of the musicians so that their exciton oscillations are likely to be knocked out of tune, causing their delicate quantum coherence to be lost.

This challenge is familiar to physicists and engineers attempting to build devices such as quantum computers. They tend to use two main strategies to keep the noise at bay. First, whenever they can, they cool their systems down to very close to absolute zero. At these very low temperatures, the molecular vibrations are damped, which in turn subdues the molecular noise. Second, they shield their equipment within the molecular equivalent of a sound studio, thereby keeping any environmental noise at bay. There are no sound studios inside living cells, and plants and microbes live in hot environments, so how do photosystems maintain their tuneful quantum coherence for so long?

The answer appears to be that photosynthetic reaction centers exploit two varieties of molecular noise to maintain rather than destroy coherence. The first is a relatively weak and low-level noise, sometimes called white noise, which is rather like TV or radio static that is spread across all frequencies.*2 This white noise comes from the thermal molecular jostling of all the surrounding molecules, such as water or metal ions, that are packed inside living cells. The second kind, sometimes called colored noise, is “louder” and limited to certain frequencies, just as colored (visible) light is limited to a narrow range of frequencies on the electromagnetic spectrum. The source of colored noise is the vibrations of the larger molecular structures within the chloroplasts, such as the pigment (chlorophyll) molecules and the protein scaffolds that hold them in place, which are composed of strings of amino-acid beads that are bent and twisted into shapes suitable for housing pigment molecules. Their bends and twists are flexible and they can vibrate, but they do so only at certain frequencies, rather like the strings of a guitar. The pigment molecules themselves also have their own vibrational frequencies. These vibrations generate the colored noise that, like a musical chord, is composed of just a few notes. Both white and colored noise appear to be exploited by photosynthetic reaction systems to help shepherd the coherent exciton to the reaction center.

A clue to how life exploits this type of molecular vibration was discovered independently by two groups in 2008–9. One was the then UK-based husband-and-wife team of Martin Plenio and Susana Huelga, who had long been interested in the effects of external “noise” on the dynamics of quantum systems and so were not surprised when they heard about Graham Fleming’s 2007 experiment on photosynthesis that we discussed in chapter 4. They quickly published several, now widely cited, papers providing a model of what they thought was going on.1 They proposed that the noisy interior of a living cell might act to drive quantum dynamics and maintain quantum coherence in photosynthetic complexes and other biological systems rather than destroy it.

The other group, across the Atlantic, was that MIT-based quantum information team led by Seth Lloyd who initially thought quantum mechanics in plants was a crackpot idea. Together with colleagues from nearby Harvard University, Lloyd took a closer look at the algal photosynthetic complex in which Fleming and Engel had detected quantum beating.2 They showed that transporting the quantum coherent exciton can be either retarded or assisted by environmental noise, depending on just how loud that noise is. If the system is too cold and quiet, then the exciton tends to oscillate aimlessly without actually getting anywhere in particular; whereas in a very hot and noisy environment something called the quantum Zeno effect kicks in, which retards quantum transport. Between these two extremes is a Goldilocks zone where vibrations are just right for quantum transport.

The quantum Zeno effect is named after the ancient Greek philosopher Zeno of Elea, who posed philosophical problems in the form of a set of paradoxes, one of which is known as the arrow paradox. Zeno considered an arrow in flight that, he argued, must inhabit a particular position in space for every instant of time. If the arrow could be glimpsed at that instant then it would be indistinguishable from a truly motionless arrow suspended in the same position. The paradox is that the flight of an arrow consists of a sequence of these frozen slices in time, with a motionless arrow at each point along its path. Yet when you put all the slices together, the arrow moves. So how can a sequence of such zero motions ever add up to real motion? The answer, we now know, is that a finite duration of time is not made up of a sequence of indivisible units of zero time. But that resolution had to wait until the invention of calculus in the seventeenth century, more than two thousand years after Zeno posed his puzzle. Nevertheless, Zeno’s paradox survives, at least in name, in one of the most peculiar features of quantum mechanics. Quantum arrows really can be frozen in time by the act of observation.

In 1977, physicists at the University of Texas published a paper that showed how something akin to Zeno’s arrow paradox can occur in the quantum world.3 The quantum Zeno effect, as it came to be known, describes how continuous observations can prevent quantum events from happening. For example, a radioactive atom, if observed closely and continuously, will never decay—an effect often described in terms of the old adage “the watched pot never boils.” Real pots do, of course, eventually boil; time only seems to slow down when you badly need a cup of tea. However, as Heisenberg pointed out, in the quantum realm the act of watching (measuring) inevitably alters the state of the thing that is being watched.

To see how Zeno’s paradox is relevant to life, we will return to the energy transport step of photosynthesis. Let’s imagine that a leaf has just picked up a solar photon and converted its energy to an exciton. Considered classically, the exciton is a particle that is localized in space and time. But, as the double-slit experiment revealed, quantum particles also possess a diffuse wave character that enables them to exist in multiple places simultaneously as a quantum superposition. It is the exciton’s waviness that is essential for efficient quantum transport, for this enables it, like a water wave, to explore multiple paths simultaneously. But if its quantum waviness breaks on the molecularly noisy rocks of decoherence inside the leaf, then its waviness will be lost and it will become a localized particle stuck in a single position. The noise essentially acts as a kind of continuous measurement, and if it is very intense then decoherence will take place very quickly, before quantum coherence has a chance to help the exciton wave reach its destination. This is the quantum Zeno effect: constantly collapsing the quantum wave into the classical world.

When the MIT team estimated the influence of molecular noise/vibrations in the bacterial photosynthetic complex, they discovered that quantum transport was optimal at temperatures around those at which microbes and plants perform photosynthesis. This perfect match between optimal transport efficiency and the kind of temperatures in which living organisms live is remarkable and, the team claim, suggests that three billion years of natural selection have fine-tuned the quantum-level evolutionary engineering of exciton transport to optimize the most important biochemical reaction in the biosphere. As they argue in a later paper, “natural selection tends to drive quantum systems to the degree of quantum coherence that is ‘just right’ for attaining maximum efficiency.”4

However, good molecular vibrations are not just limited to the white noise variety. “Colored” noise, generated by a limited set of vibrations of the chlorophyll molecules themselves, or even the surrounding proteins, is now also thought to play a key role in keeping decoherence at bay. If we imagine the white thermal noise as a molecular version of the static on a badly tuned radio, then the good vibrations of colored noise are akin to a simple beat like the Beach Boys’ “bop bop” in their song “Good Vibrations.” But remember that the exciton also behaves in a wave-like manner to generate those coherent quantum beats that Graham Fleming’s group detected. Two recent papers from Martin Plenio’s group at the University of Ulm in Germany in 2012 and 2013 demonstrated that if the oscillation of the exciton and the oscillations of the surrounding proteins—the colored noise—are beating to the same drum then, when the coherent exciton gets knocked out of tune by the white noise, it can be knocked back into tune by the protein oscillations.5 Indeed, in a 2014 Nature paper, Alexandra Olaya-Castro at University College London showed in a beautiful theoretical study that the exciton and the molecular vibrations—the colored noise—share a single quantum of energy in a way that simply cannot be explained without recourse to quantum mechanics.6

To fully appreciate the contributions of the two kinds of molecular noise to exciton transport, let us return to a musical metaphor once again and imagine the photosystem is an orchestra, with the various instruments playing the role of the pigment molecules, and the exciton is a musical tune. We imagine that the music opens with a violin solo, representing the pigment molecule that captures the photon and converts its energy into a vibrating exciton. The music of the exciton is then picked up by the other string instruments, then the wind instruments, and eventually reaches the percussion, whose rhythm plays the role of the reaction center. We will further imagine that this music is playing in a theater packed with an audience who will provide the white noise of crisp packets being opened, chairs being shuffled, coughs and sneezes. The conductor will be the colored noise.

Let’s first imagine we have arrived on a very rowdy night, with the audience making such a racket that the musicians cannot hear either themselves or their colleagues. In all the hubbub, the first violin begins the piece but the other musicians cannot hear it and so are unable to pick up the melody. This is the quantum Zeno scenario, where too much noise is preventing quantum transport. However, at very low levels of noise, say in an empty theater without any audience present, the musicians are only listening to one another, so they all pick up the first melody, like a tune that you can’t get out of your head, and keep playing it. This is the opposite scenario of too much quantum coherence, where the exciton remains oscillating throughout the whole system but doesn’t end up anywhere in particular.

In the Goldilocks zone, with just the right amount of noise delivered by a self-controlled audience, the disturbance is sufficient to jog the musicians out of their monotonous repetition to play the full score with all its dynamics. Some of the instruments are still knocked into a different beat when an occasional crisp bag is popped by a rowdy spectator, but, with a wave of his baton, the conductor is able to bring them back into sync to deliver the music of photosynthesis.

Reflections on the motive force of life

In chapter 2 we peered inside a steam engine to discover that its motive force involved capturing the random motion of the sea of billiard-ball-like molecules and directing the molecular turbulence toward driving the piston within the cylinder. We then asked whether life can be entirely accounted for by the same “order from disorder” thermodynamic principle that drives steam engines. Is life just an elaborate steam engine?

Many scientists are convinced that it is, but in a subtle way that needs a little elaboration. Complexity theory studies the tendency of certain forms of random chaotic motion to generate order through the phenomenon of self-organization. For example, as we have already discussed, the molecules within liquids are moving entirely chaotically, yet when your bathtub is draining the water spontaneously flows around the drain in an orderly clockwise or counterclockwise direction. This macroscopic order can also be seen in the patterns of convection flow in a heated pot of water, in hurricanes, tornadoes, the red spot on Jupiter and many other natural phenomena. Self-organization is also involved in several biological phenomena, such as the swarming behavior of birds, fish or insects, or in the pattern of stripes of a zebra, or in the complex fractal structure of some leaves.

What is remarkable about all these systems is that the macroscopic order we can see is not reflected at the molecular level. If you had a very powerful microscope that could reveal the individual molecules that were flowing down your drain you might be surprised to see that their motions are nearly entirely random, with just a very slight bias from randomness in a clockwise or counterclockwise direction. At a molecular level, there is only chaos—but chaos with a slight bias that can generate order at a macroscopic level: order from chaos, as this principle is sometimes termed.7

Order from chaos is conceptually quite similar to Erwin Schrödinger’s “order from disorder,” which, as we have already described, lies behind the motive force of steam engines. But, as we have discovered, life is different. Although there is plenty of disorderly molecular motion inside living cells, the real action of life is a tightly choreographed motion of fundamental particles within enzymes, photosynthetic systems, DNA and elsewhere. Life has built-in order at a microscopic level; and so “order from chaos” cannot be the only explanation for life’s fundamental distinguishing features. Life is nothing like a steam train.

However, recent research suggests that life may operate along the lines of a quantum version of the steam engine.

The principle of how steam engines work was first outlined in the nineteenth century by a Frenchman, Sadi Carnot. He was the son of Napoleon’s minister of war, Lazare Carnot, who obtained a commission in the engineer corps of Louis XVI’s army. After the king was deposed, Lazare Carnot did not, like many of his aristocratic colleagues, flee the country, but instead joined the revolution; and, as war minister, he was largely responsible for creating the French revolutionary army that repelled the Prussian invasion. But as well as being a brilliant military strategist, Lazare was also a mathematician, a lover of music and poetry (he named his son after the medieval Persian poet Saadi Shirazi) and an engineer; he wrote a book on how machines convert one form of energy into another.

Sadi exhibited some of his father’s revolutionary and nationalistic fervor, taking part in the defense of Paris as a student in 1814 when the city was once again besieged by the Prussians. He also demonstrated some of his father’s engineering insight, writing a remarkable book entitled Reflections on the Motive Force of Fire (1823), which is often credited as initiating the science of thermodynamics.

Sadi Carnot drew inspiration from the design of steam engines. He believed that France had been defeated in the Napoleonic wars because it hadn’t harnessed the power of steam to build heavy industry in the way that England had. However, although the steam engine had been invented and successfully commercialized in England, its design had been mostly down to trial and error and the intuition of engineers such as the Scottish inventor James Watt. What it lacked was any theoretical foundation. Carnot sought to rectify this situation by describing in mathematical terms how any heat engine, such as those that drove steam trains, could be used to do work via a cyclical process that is to this day known as the Carnot cycle.

The Carnot cycle describes how a heat engine transfers energy from a hot to a cold place and harnesses some of this energy to do useful work, before returning to its initial state. For example, a steam engine transfers heat from the hot boiler to the condenser, where it is cooled, and in the process harnesses some of the heat energy as steam to do the work of moving a piston and thereby the wheels of a locomotive. The cooled water is then returned to the boiler ready to be heated up again for another round of the Carnot cycle.

The principle of the Carnot cycle applies to all kinds of engines that use heat to do any sort of work, from the steam engines that powered the industrial revolution to the gas engine that drives your car or the electrical pump that cools your fridge. Carnot showed that the efficiency of each of these—in fact, “every imaginable heat engine,” as he put it—depends on a few fundamental principles. Moreover, he proved that the efficiency of any classical heat engine cannot exceed a theoretical maximum, now known as the Carnot limit. For example, an electric motor that is using 100 watts of electric power to supply 25 watts of mechanical power has an efficiency of 25 percent: it is losing 75 percent of its supplied energy as heat. Classical heat engines are not very efficient.

The principles and limitations of Carnot heat engines are extraordinarily broad and can even be applied to photocells, such as those found on the roofs of some buildings, that capture light energy and convert it into electricity. The same is true of the biological photocells in the chloroplasts of leaves that we have described in this book. Such a quantum heat engine does a similar job to a classical heat engine, but with electrons instead of steam and photons of light replacing the heat source. Electrons first absorb photons and are excited to a higher energy. They can then give up this energy, when required, to do useful chemical work. This idea goes back to the work of Albert Einstein and would later underpin the principles of the laser. The problem is that many of these electrons will lose their energy as wasted heat before they have a chance to put it to use. This puts a limit on the efficiency of such a quantum heat engine.

You will remember that the reaction center is the final destination for all those oscillating excitons in photosynthetic complexes. So far, we have focused on the energy delivery process; but the real action of photosynthesis takes place in the reaction center itself. Here the fragile energy of excitons is converted into the stable chemical energy of the electron carrier molecule that plants or microbes use to do lots of useful work, like building more plants and microbes.

What takes place in the reaction center is just as remarkable as the exciton transport step, and even more mysterious. Oxidation is the chemical process by which electrons are moved between atoms. In many oxidations, electrons actively hop from one atom (which becomes oxidized) to another. But in other oxidations, such as the burning of coal, wood or any carbon-based fuel, electrons that are initially possessed solely by one atom end up being shared with other atoms: a net loss of electrons to the electron donor (just as sharing your chocolate bar involves a net loss of chocolate). So, when carbon is burnt in air, electrons in its outer orbits end up being shared with oxygen to form the molecular bonds of carbon dioxide. In these burning reactions the outer electrons of carbon are only relatively loosely bound, so they are relatively easy to share. But in the photosynthetic reaction center of a plant or microbe, energy is used to pluck electrons right out of water molecules in which the electrons are far more tightly bound. Essentially, a pair of H2O molecules is split to produce one O2 molecule, four positively charged hydrogen ions and four electrons. So, since water molecules lose their electrons, the reaction center is the only natural place where water is oxidized.

In 2011 the American physicist Marlan Scully, currently a professor jointly at Texas A&M University and Princeton, along with his coworkers at several US universities, described a clever way for a hypothetical quantum heat engine to be engineered to exceed the efficiency limits of a standard quantum heat engine.8 To do this, molecular noise is used to nudge an electron into a superposition of two energy states at the same time. When this electron then absorbs the energy of a photon and is “excited,” it will remain in a superposition of two (now higher) energies at once. Now the probability of the electron falling back to its original state and losing its energy as wasted heat can be reduced, thanks to the quantum coherence of its two energy states—this is similar to the example of the interference pattern produced by the double-slit experiment we described in chapter 4. There, certain positions on the back screen that are available to the atom when just one slit is open become inaccessible owing to destructive interference when both slits are open. Here, the delicate collaboration between molecular noise and quantum coherence tunes a quantum heat engine to reduce inefficient wastage of thermal energy and thereby increase its efficiency beyond the quantum Carnot limit.

But is such delicate tuning at the quantum level possible? You would need to engineer at a subatomic scale both the position and the energies of individual electrons to deliver just the right amount of interference to increase the flow of energy along efficient paths and eliminate flow down the wasteful ones. You would also need to tune the surrounding molecular white noise so that it would nudge the off-beat electrons into the same beat—but not too vigorously, or they would be knocked into different rhythms and coherence would be lost. Is there anywhere in the universe where we might expect to find this finely tuned degree of molecular order capable of exploiting delicate quantum effects in the subatomic world?

Scully’s 2011 paper was entirely theoretical. No one has yet built a quantum heat engine that can capture the expected Carnot-busting energy bonus. But in 2013 another paper from the same team pointed out a curious fact regarding photosynthetic reaction centers.9 They are all equipped, not with a single chlorophyll molecule that might be able to operate a straightforward quantum heat engine, but with a pair of chlorophyll molecules known as a special pair.

Although the chlorophyll molecules in the special pair are identical, they are embedded in different environments in the protein scaffold, which makes them vibrate at slightly different frequencies: they are slightly out of tune. In their later paper, Scully and his colleagues pointed out that this structure provides photosynthetic reaction centers with the precise molecular architecture needed for them to work as quantum heat engines. The researchers showed that the chlorophyll’s special pair appears to be tuned to exploit quantum interference to inhibit inefficient wasteful energy routes and thereby deliver energy to the acceptor molecule with about 20 percent higher efficiency. That may not seem a huge amount until we consider the current estimate that world energy consumption will grow by about 56 percent between 2010 and 2040: then developing a technology capable of boosting solar energy capture by a comparable margin could be very interesting. These findings remain controversial in the fast-evolving field; however, a more recent study from the University of Ulm10 confirms many aspects of the quantum heat engine hypothesis.

This extraordinary result provides yet another remarkable example of how living organisms rooted in the quantum world seem to have abilities denied to inanimate macroscopic machines. Of course, quantum coherence is necessary for this scenario to work; but in another result published in July 2014, a team of researchers from the Netherlands, Sweden and Russia detected quantum beating in plant photosystem reaction center II*3 and went on to claim that these centers function as “quantum-designed light traps.”11 And remember that photosynthetic reaction centers evolved between two and three billion years ago. So for nearly the entire history of our planet, plants and microbes seem to have been utilizing quantum-boosted heat engines—a process so complex and clever that we have yet to work out how to reproduce it artificially—to pump energy into carbon and thereby make all the biomass that formed microbes, plants, dinosaurs and, of course, us. Indeed, we are still harvesting ancient quantum energy in the form of fossil fuels that warm our homes and power our cars and drive most of today’s industry. The potential benefits of modern human technology learning from ancient natural quantum technology are huge.

So, in photosynthesis, noise seems to be utilized both to enhance the efficiency of delivery of excitons to the reaction center and to capture that solar-derived energy once it arrives in the reaction center. But this ability to make a quantum virtue out of a molecular vice—noise—is not limited to photosynthesis. In 2013, Nigel Scrutton’s group at the University of Manchester, the team who studied proton tunneling in enzymes in the experiments that we discussed in chapter 3, replaced the regular atoms in an enzyme with heavier isotopes. The isotope exchange had the effect of adding extra weight to the protein’s molecular springs so that they vibrated—its colored noise—at different frequencies. The researchers found that proton tunneling and enzyme activity were perturbed in the heavier enzyme,12 suggesting that in the normal state with the natural, lighter isotopes, the metronome-like oscillations of its protein backbone contribute to tunneling and enzyme activity. Similar results, with other enzymes, have been obtained by Judith Klinman’s group at the University of California.13 So, as well as guiding photosynthesis, noise appears also to be involved in boosting enzyme action. And remember that enzymes are the engines of life that have made every single molecule inside every cell of every living creature on our planet. Good vibrations may be playing a crucial role in keeping us all alive.

Life on the quantum edge of a classical storm

On a ship at sea: a tempestuous noise

WILLIAM SHAKESPEARE, The Tempest, ACT I, SCENE 1, OPENING STAGE DIRECTION

Do any of these insights provide an answer to the question Schrödinger posed decades ago about the nature of life? We have already taken on board his insight that life is a system dominated by order that goes all the way down, from highly organized whole organisms through the stormy thermodynamic ocean to the quantum bedrock below (figure 10.1). And, crucially, these dynamics of life are delicately poised and balanced so that quantum-level events can make a difference to the macroscopic world, just as Pascual Jordan predicted in the 1930s. This macroscopic sensitivity to the quantum realm is unique to life and allows it potentially to exploit quantum-level phenomena, such as tunneling, coherence and entanglement, to make a difference to us all.

But, and this is a big but, this exploitation of the quantum world can only take place if decoherence can be kept at bay. Otherwise the system loses its quantum character and behaves entirely classically or thermodynamically, relying on the “order from disorder” rules. Scientists have fended off decoherence by shielding their quantum reactions from intrusive “noise.” This chapter has revealed that life appears to have adopted a very different strategy. Instead of allowing noise to hinder coherence, life uses noise to maintain its connection to the quantum realm. In chapter 6, we imagined life as a granite block delicately poised to render it susceptible to quantum-level events. For reasons that will become clear in a moment, we will make a metaphorical shift by replacing our granite block with a tall sailing ship.

Our imaginary sailing ship will initially be in dry dock, with its narrow keel exquisitely balanced on a single line of carefully aligned atoms. In this perilously poised state our ship, like a living cell, is sensitive to quantum-level events taking place in its atomic keel. The tunneling of a proton, the excitation of an electron or the entanglement of an atom can all have an influence on the entire ship, perhaps by affecting its delicate balance on the dry dock. However, we will further imagine that its captain has found clever and surprising ways to make good use of these delicate quantum phenomena such as coherence, tunneling, superposition or entanglement to help navigate his craft once it sets sail.

But remember that we are still in dry dock: this ship isn’t going anywhere just yet. And although in its delicately balanced state it can potentially harness quantum-level phenomena, its precarious perch leaves it vulnerable to even the faintest imaginable breeze—perhaps being touched by just a single air molecule—which could topple the whole vessel. The engineer’s approach to the problem of keeping the craft upright and thus retaining its sensitivity to the quantum events in its keel would be to enclose the ship in a shielded box and pump out all the air to prevent any stray billiard-ball-like molecule from disturbing the vessel. The engineer would also cool the entire system down to close to absolute zero so that not even a molecular vibration could disturb its delicate balance. But skilled sea captains know that there is another way to keep a ship upright: it must first be launched into turbulent thermodynamic waters.

We take it for granted that a ship is easier to keep upright in water than on land, but thinking about it at a molecular level we find that the reason for its increased stability isn’t immediately obvious. We have just said that an engineer’s approach to keeping a narrow-keeled ship upright in dry dock would be to protect the vessel from any potential disturbance from stray atoms or molecules. But isn’t the sea full of stray atoms and molecules randomly jostling one another and the keel of any ship in that billiard-ball fashion that we explored in chapter 2? How is it that the precariously balanced ship can be toppled by tiny impacts on land but remains impervious to them when on the water?

Figure 10.2: Life navigates the edge of the quantum and classical worlds. The living cell is like a ship whose narrow keel penetrates right down to the quantum layer of reality and can thereby capture phenomena such as tunneling or entanglement to keep itself alive. This connection to the quantum realm has to be actively maintained by living cells harnessing the thermodynamic storms—molecular noise—to maintain, rather than disrupt, quantum coherence.

The answer comes back to those “order from disorder” rules that Schrödinger described. The ship will indeed be bombarded with trillions of molecular impacts from both its port and starboard sides. Of course, it is now no longer balancing on its ultrathin keel but kept afloat by the buoyancy of the water, and with so many impacts on both sides of the ship, the average force to the bow and stern or to port and starboard will be the same. So buoyant ships do not topple because they are being held up by trillions of random molecular bombardments: order (the ship’s vertical orientation) from disorder (trillions of random billiard-ball-like molecular impacts).

But ships can of course be toppled, even on the high seas. Imagine that the captain has launched his ship onto a tempestuous sea, but hasn’t yet hoisted its sail. The waves buffeting the vessel aren’t so random anymore, and big swells may surge from one side or another that could easily topple an unstable vessel. But our clever captain knows how to increase the stability of his ship: he hoists the sails so that he can harness the power of the wind to keep his vessel on an even keel (figure 10.2).

Once again, this stratagem may, at first sight, appear to be contradictory. We would expect that haphazard winds and unpredictable gusts would act to topple rather than stabilize an already unsteady ship—particularly as they won’t be random but will tend to arrive with more force on one side of the ship or the other. But the captain knows how to adjust the angle of the sail and the tiller so that the action of the wind and currents acts against the gusts and the gales to correct any listing to one side or the other. In this way, he can harness the surrounding tempest to keep his ship stable.

Life, it seems, is like that metaphorical ship sailing through stormy classical waters with a clever captain on board: the genetic program, honed by nearly four billion years of evolution, is able to navigate the various depths of the quantum and classical realms. Rather than hiding from the tempests, life embraces them, marshaling their molecular squalls and gales to fill its sails and keep the ship upright so that its narrow keel penetrates the thermodynamic waters to connect with the quantum world (figure 10.2). Life’s deep roots allow it to harness those weird phenomena that prowl the quantum edge.

Figure 10.3: Perhaps death represents the severing of the living organism’s connection with the orderly quantum realm, leaving it powerless to resist the randomizing forces of thermodynamics.

Does this provide us with a new insight into what life really is? Well, there is one further speculation, and we emphasize that it is indeed speculation, but one that, having journeyed this far, we cannot resist making. Remember the question that we posed in chapter 2 concerning the difference between the living and the lifeless, that difference that the ancients described as our soul? Death, they believed, was brought about by the departure of the soul from the body. Descartes’s mechanistic philosophy expelled vitalism and discarded the soul, at least from plants and animals, but the difference between the living and the dead remained mysterious. Can our new understanding of life replace the soul with a quantum vital spark? Many will regard the very posing of this question as suspect, pushing the boundaries of conventional science beyond respectability and into the realms of pseudoscience or even a kind of spirituality. That is not what we are proposing here. Instead, we want to offer what we hope is an idea that might replace mystical and metaphysical speculations with at least the grain of a scientific theory.

In chapter 2, we compared the capacity of life to preserve its highly organized state to a billiard-table contraption that could maintain a triangle of balls in the center of the table by detecting and replacing any balls knocked out of place by the collisions from other balls in a thermodynamic-like system. Now that you have discovered more about how life works, you can see that this self-sustainability is maintained by the complex molecular machinery of enzymes, pigments, DNA, RNA and other biomolecules, some of whose properties depend on quantum mechanical phenomena such as tunneling, coherence and entanglement.

The recent evidence that we have examined in this chapter suggests that some or all of these diverse quantum-boosted activities, which we could imagine as the activities taking place on the busy deck of our ship, are maintained by life’s remarkable ability to harness thermodynamic storms and gales to retain its connection with the deeper quantum realm. But what happens if the thermodynamic storm blows too strongly, metaphorically breaking the ship’s mast? No longer able to harness the thermodynamic gusts and gales—the white and colored noise—to maintain an even keel, the sail-less cell will be buffeted by the waves and swells of its interior, causing our metaphorical ship to pitch and roll, eventually severing its connection with the orderly quantum realm (figure 10.3). Without this connection, coherence, entanglement, tunneling or superposition can no longer influence the cell’s macroscopic behavior, so the quantum-disconnected cell will sink beneath the thermodynamically turbulent waters, becoming an entirely classical object. Once a ship has sunk, no storm will refloat it; and perhaps, once a living organism has been captured by the stormy ocean of molecular motion, no tempest can restore its quantum connection.

Can we exploit quantum biology to make new living technology?

Storms may not be able to refloat a sunken boat, but humans can. Human ingenuity can achieve so much more than random forces. As we discussed in chapter 9, the probability of a tornado blowing mindlessly through a junkyard and assembling a jumbo jet through sheer chance is stupendously tiny. But aviation engineers can build planes. Can we also assemble life? As we have pointed out on several occasions in this book, no one has yet succeeded in making life out of inert chemicals, which, according to Richard Feynman’s famous dictum, means that we do not yet fully understand the phenomenon of life. But perhaps our newfound understanding of quantum biology can provide us with the means to create new life and even build a revolutionary form of living technology.

Living technology is of course familiar. We are completely dependent on it, in the form of agriculture, to make our food. We also rely on the products of living technology, such as the bread, cheese, beers and wines that have been transformed from flour, milk, grain and fruit juices by yeast and bacteria. Our modern world similarly benefits from its harvest of the nonliving products of once-living cells, such as the enzymes that Mary Schweitzer used to break down dinosaur bone. Similar enzymes are used to break down natural fibers to make the fabrics for clothes or are added to the biological detergents that wash those clothes. The multimillion-dollar biotechnology and pharmacology industries produce hundreds of natural products, such as the antibiotics that protect us from infection. The energy industry exploits the ability of microbes to turn excess biomass into biofuels; and many of the materials that support modern life, such as timber and paper, were once alive, as were the fossil fuels that heat our homes and power our cars. So even in the twenty-first century we remain extraordinarily reliant on our millennia-old living technology. If you harbor any remaining doubts, try reading Cormac McCarthy’s The Road, a dystopian novel describing the bleak world that would be left to us if we carelessly destroyed our living technology.

But the existing living technology has its limitations. For example, although—as we have discovered—some of the steps in the process of photosynthesis are extraordinarily efficient, most are not, and the overall energy efficiency of the conversion of solar energy into chemical energy that we can harvest in agriculture is very low. The reason is that plants and microbes have a different agenda from ours: they carry out inefficient chores like making flowers and seeds that are not really necessary for energy capture but are nevertheless essential for their own survival. Similarly, the microbes that make antibiotics, enzymes or pharmaceuticals do so very wastefully because their evolution-honed agenda forces them to make lots of unnecessary stuff, like more microbial cells.

Can we engineer life that sticks to our agenda? Of course we can, and we already benefit hugely from humankind’s successful transformation of wild plants and animals into the living technology of domesticated crops and livestock, optimized for human exploitation. But the process of artificial selection that gave us plants with bigger seeds or docile animals suitable for farming, although highly successful, has its limitations. We cannot select what nature has not already fashioned. For example, billions of dollars are spent each year on fertilizers that replenish the soil’s nitrogen, lost through intensive agriculture. Leguminous crops, such as peas, don’t need nitrogen fertilizers because they harbor bacteria in their roots that capture the gas directly from the air. Agriculture could be far more efficient if we could engineer leguminous cereal crops that fix their own nitrogen, like peas do. But this capability hasn’t evolved in any cereal.

However, even this limitation can be at least partly overcome. The genetic manipulation of plants, microbes and even animals (genetic engineering) took off in the late twentieth century. Today, much of the harvest of major crops such as soya comes from genetically engineered plants resistant to disease or herbicide, and efforts are under way to, for example, insert nitrogen-capturing genes into cereal crops. The biotechnology industry similarly relies heavily on genetically modified microbes to produce our pharmaceuticals and antibiotics.

Even so, once again there are limitations. Genetic engineering mostly just moves genes around from one species to another. For example, the rice plant makes vitamin A (beta carotene) in its leaves but not in its seed, so hardly any is present in the staple crop that feeds much of the developing world. Vitamin A is essential for our immune system and our vision, so its deficiency in the poorest rice-dependent regions of the world leads to millions of children dying of infections or becoming blind each year. In the 1990s Peter Beyer from the University of Freiberg and Ingo Potrykus from the Swiss Federal Institute of Technology in Zurich genetically inserted two genes needed to make vitamin A, one from daffodils and the other from a microbe, into the rice genome to make rice with high levels of vitamin A in its seeds. Golden rice, as Beyer called it because of the yellow color of its seeds, can now provide most of the daily vitamin A requirement for children. However, although genetic engineering is a very successful technology, it is really just tinkering with life. The new science of synthetic biology aims to make a truly revolutionary living technology by engineering entirely novel forms of life.

There are two complementary approaches to synthetic biology. The top-down approach is the one we have already met in the course of discussing how the genome-sequencing pioneer Craig Venter constructed so-called “synthetic life” by replacing the genome of a bacterium called mycoplasma with a chemically synthesized version of the same genome. This genome swap allowed his team to make relatively minor modifications to the entire mycoplasma genome. Nevertheless, it was still a mycoplasma: they did not introduce any radical changes into the bacterium’s biology. Over the coming years Venter’s team plans to engineer more radical changes; but these changes will be introduced step-by-step in this top-down synthetic biology approach. The team did not make new life: they modified existing life.

The second approach is bottom-up and is far more radical: rather than modifying an existing living organism, bottom-up synthetic biology aims to engineer completely new life forms out of inert chemicals. Many would consider such an endeavor dangerous, even sacrilegious. Is it even feasible? Well, living organisms, like us, are extraordinarily elaborate machines. Like any machine, they can be reverse-engineered to discover their design principles; and those design principles can then be harnessed to build even better machines.

Building life from the bottom up

Bottom-up synthetic life enthusiasts dream of making completely novel life forms that could transform our world. For example, today’s architects are rightly preoccupied with the notion of sustainability: sustainable houses, offices, factories and cities. However, although modern buildings or cities are often described as self-sustainable, they mostly rely on the efforts and skills of truly self-sustainable beings, humans, to keep them in shape: when your roof tiles are blown off in a storm, you hire the builder to climb up and replace them; when your pipes leak, you call the plumber; when your car breaks down, you have it towed to a mechanic. Essentially, all this manual maintenance is needed to repair the damage inflicted on our homes or machines by all that billiard-ball-like molecular jostling inflicted by wind, rain and other environmental insults.

Life is different: our bodies are able to continually maintain themselves by renewing, replacing and repairing damaged or worn-out tissue. For as long as we are alive, we are indeed self-sustainable. Modern architecture has attempted to mimic certain features of life in many of the signature buildings of recent years. For example, Norman Foster’s “Gherkin” tower, which was added to the London skyline in 2003, possesses a hexagonal skin inspired by the Venus Flower Basket Sponge (which is a sponge, not a flower) that efficiently distributes the building’s stresses. The Eastgate Centre in Harare, Zimbabwe, designed by architect Mick Pearce, mimics the air-conditioning system of termite mounds to provide ventilation and cooling. Rachel Armstrong, codirector of the architectural research group AVATAR based at the University of Greenwich, has a bolder vision: truly self-sustaining buildings, the ultimate biometric architecture. Along with several other architectural visionaries, she dreams of engineering buildings out of artificial living cells that possess the ability to sustain, self-repair and even self-replicate.14 If such living buildings were damaged by wind, rain or flood they would, like living organisms, sense their injury and self-repair just like living bodies.

Armstrong’s ideas could be extended to enhance other synthetic features of our lives. Living material could also be used to construct prosthetics, such as artificial limbs or joints, that would be able to self-repair and protect themselves from microbial attack, just like living tissue. Artificial life forms could even be injected into the human body to, for example, search out and destroy cancer cells. Pharmaceuticals, fuels and food could all be made by custom-engineered synthetic life forms unencumbered by any evolutionary history. Further into the future is the sci-fi vision of living robots, androids, which could take over the menial tasks of society or even “terraform” Mars to make it habitable for human colonies, or construct living spaceships that could explore the galaxy.

The idea of the bottom-up creation of synthetic life can be traced back to the early twentieth century, when the French biologist Stéphane Leduc wrote that, “just as synthetic chemistry began with artificial formation of the simplest organic products, so biological synthesis must content itself at first with the fabrication of forms resembling those of the lowest organisms.”15 As we discussed in chapter 9, even the “lowest organisms” alive today are actually extraordinarily complex bacteria made up of thousands of parts that cannot currently be synthesized by any conceivable bottom-up approach. Life must have started from something much simpler than a bacterium. Today’s best guesses for our ultimate ancestor are, as we suggested in that chapter, molecules of self-replicating enzymatic RNA (ribosomes) or protein that became enclosed within some kind of small vesicle to form a self-replicating simple cellular structure, a protocell. The nature of the first protocells, if they indeed existed, is not at all clear. Many scientists believe they sheltered within microscopic pores in rocks, such as the Isua rocks that we met in chapter 9, filled with simple biochemicals capable of supporting life. Others believe that they were bubbles or droplets of biochemicals bounded by some kind of membrane floating in the primordial ocean.

Most bottom-up synthetic life enthusiasts take inspiration from origin-of-life theories by attempting to build their own artificial living protocells capable of swimming through a laboratory-based primordial sea. Probably the simplest are the various kinds of droplets or vesicles of oil in water or water in oil. These are easy to make; in fact, you have made millions of them whenever you made a salad dressing. Oil and water famously don’t combine and so will quickly separate; but if you add a substance whose molecules embed between water and oil, a surfactant such as mustard, and give the mixture a good shake, you make a salad dressing. Although this may look smooth and homogeneous, in reality it is filled with trillions of tiny stable oil droplets.

Martin Hanczyc of the University of Southern Denmark has made remarkably lifelike protocells out of oil-in-water droplets that are stabilized by detergent. His protocells are very simple, often constructed from only five chemicals. Mixed in the right proportions, they self-assemble into oily droplets. The interior of the droplets supports a simple chemistry that causes the protocell to move through its environment, propelled by convection (heat circulation) and the same kind of chemical forces that cause oil droplets to coalesce in the first place. They are even able to undergo a simple form of growth and self-replication by absorbing raw materials from their environment, eventually causing them to break in two.16

Hanczyc’s protocells are inside-out compared to living cells, as they have an oily interior and water on the outside. Most other researchers opt for making protocells with a watery interior. This also allows them to fill them with ready-made water-soluble biomolecules. For example, in 2005 the geneticist Jack Szostak filled protocells with RNA ribozymes.17 Remember (chapter 9) that ribozymes are RNA molecules that can encode genetic information, just like DNA, but also host enzyme activity. The team showed that the ribozyme-filled protocells were capable of a simple form of heredity, essentially splitting in two like Hanczyc’s protocell. In 2014 a team led by Sebastien Lecommandoux based at Radboud University in the Netherlands made another kind of protocell whose multiple compartments were filled with enzymes that could, like living cells, support a simple metabolism that cascaded from one compartment to another.18

These dynamic, chemically active protocells are certainly intriguing and impressive constructions; but are they life? To answer this question we need to agree on a working definition of life. The obvious one, self-replication, is fine for many purposes, but it asks too much. Most of the cells in an adult body, such as red blood cells and nerve cells, do not replicate, yet they are undoubtedly alive. Even whole humans, such as Buddhist or Catholic priests, don’t (usually) bother with the messy business of self-replication, yet they remain very much alive. So, although self-replication is of course necessary for the long-term survival of any species, it is not an obligatory property of life.

A property of life that is even more fundamental than self-replication is the one that we have already discussed and which biomimetic architects strive to emulate: self-sustainability. Life is able to sustain its living state. So the minimum requirement we will demand for our bottom-up protocells to earn classification as living is that they must be capable of sustaining themselves in turbulent thermodynamic seas.

Unfortunately, using this more limited definition of life, none of the existing generation of protocells is alive. Even those that can perform a few tricks, like a simple form of replication (splitting in two), produce daughters that are not really the same as the parents: they have less of the starting components, such as ribozymes or enzymes, so that, as the replication process proceeds, these components are eventually exhausted. Similarly, although protocells such as those made by Lecommandoux’s group are able to support a metabolism resembling that of a simple living organism, they need to be filled with active biomolecules, which they are not capable of replenishing themselves. The current generation of protocells are like wound-up clocks: they can maintain their chemical start-up state, supported by premade enzymes and substrates, until it runs down. Thereafter, the continual battering received from the surrounding molecular motion erodes the organization of these protocells so that they become progressively more chaotic and random until they are eventually no different from their environment. Artificial protocells are, unlike life, incapable of winding themselves up.

Are they missing an ingredient? The field is of course very young, and it is likely that great strides will be made in the coming decades. The idea we want to explore in this last section of our book is that quantum mechanics could provide the missing spark needed to animate artificial life and make truly synthetic life. As well as launching a revolutionary technology, such an advance might also finally provide us with the means to answer that ancient question that we posed in chapter 2: What is life?

We, and others, have argued that the thermodynamic description of life is inadequate as it does not incorporate life’s ability to harness the quantum realm. Life, we believe, depends on quantum mechanics. But are we right? As we have already discussed, this is hard to prove with the technology we have today, because you can’t just turn quantum mechanics off and on in a living cell. However, we predict that life, whether natural or artificial, is impossible without the strange features of the quantum world we have discussed in this book. The only way to find out if we are right is to make synthetic life with and (if possible) without quantum weirdness and see which one works best.

Launching the primordial quantum protocell

Let us imagine building a simple living cell out of totally inanimate material, perhaps one able to perform simple tasks, such as finding its own food within a kind of laboratory-maintained primordial sea. Our aim will be to build such a device in two ways. One will seek to harness the weird features of quantum mechanics—we will call it the quantum protocell. The other will not—this will be the classical protocell.

A good starting point for both versions would be Sebastien Lecommandoux’s multicompartment, membrane-bounded protocells, the different sections of which allow us to separate the distinct functions of life into individual compartments. Next, we need to provide our protocell vessel with an energy source: let’s use that abundant source of high-energy photons, sunlight. We will load one of its compartments with a forest of pigment molecules and scaffold proteins, making a form of solar panel, able to capture photons and convert their energy into excitons, like an artificial chloroplast. However, jumbled-up pigment molecules will be unlikely to deliver the high-efficiency energy transport characteristic of photosynthesis, since the molecular muddle will be unable to maintain the quantum coherence needed for efficient energy transport. To capture the quantum beat we need to orientate the pigment molecules so that the coherent wave can flow through the system.

In 2013, a University of Chicago group led by quantum photosynthesis pioneer Greg Engel tackled this problem by chemically bolting pigment molecules together in a fixed alignment. Just like the algal FMO complex in which Engel had first detected quantum coherence (chapter 4), their artificial pigment system showed coherent quantum beats that continued for tens of femtoseconds, even at room temperature.19 So, to provide the solar panel of our quantum protocell with coherence-boosted excitons, we will fill it with a forest of Engel’s bolted-together pigment molecules. The classical photocell will contain the same pigments, but they will be randomly aligned so that the exciton will have to meander its way through the system. We could thereby test whether quantum coherence is essential or dispensable for exciton transport in photosynthesis.

However, as we have discovered, catching light is only the first step in the job of photosynthesis; we next need to transform the unstable exciton energy into a stable chemical form. Once again, some progress has already been made. When the Scully group demonstrated in their 2013 paper that the photosynthetic reaction center appears to be a quantum heat engine, they went on to argue that biological quantum heat engines could inspire the design of more efficient photocells.20 Later that same year, a team from the University of Cambridge took them at their word and produced a detailed blueprint for such an artificial photocell that would work as a quantum heat engine.21 The group modeled an artificial reaction center from the bolted-together pigment molecule made in Engel’s laboratory and showed that it should deliver an energetic electron to an acceptor molecule with a similar Carnot limit-busting efficiency enhancement as the Scully group had discovered for natural photosynthesis.

So let us imagine our quantum solar cell rigged onto an artificial reaction center, inspired by the Cambridge team’s model, that is able to capture energetic electrons as stable chemical energy. Once again, we will engineer a rival system for our classical protocell that attempts a similar energy transfer process, but without the quantum Carnot-busting efficiency. Once the light energy has been captured, it can be used to build complex biomolecules, such as the cell’s pigment molecules.

However, as well as electrons, biosynthetic reactions need an additional energy boost that, in our own cells, is provided by cellular respiration (chapter 3). We will take inspiration from respiration and shunt some of the high-energy electrons delivered by photosynthesis into a “power plant” compartment, where they will tunnel from one enzyme to another, as in natural respiratory chains, to make ATP, the cell’s molecular energy carrier. Once again, our aim will be to engineer the respiratory compartment and to explore the role of quantum mechanics in this vital biological process.

With a source of electrons and energy, our quantum protocell is now equipped to make all its own biochemicals; but it needs a source of raw material—food. So we provide it with a food source, a simple sugar: glucose dissolved in our laboratory-based primordial sea. We will have to install ATP-powered sugar transporters, able to pump the glucose inside the cell, together with another suite of enzymes, capable of manipulating its atoms—quantum-level engineering—to build more complex biomolecules. Many of these enzymes normally utilize electron and proton tunneling, as we discussed in chapter 3, but our aim will be to engineer versions that work with and without the capability of dipping into the quantum world to discover whether quantum mechanics really provides an essential lubricant for these engines of life.

Another feature that we would like to engineer into our quantum-supported protocell is the capability of harnessing the tempest of molecular noise to maintain quantum coherence. At present, too little is known about how life manages this trick to have any confidence in how it might be engineered. Many factors may be involved: for example, the extremely crowded molecular environment of living cells is known to modify many biochemical reactions,22 and might help to restrict the randomizing impact of noise. So we will pack the protocells very tightly with biomolecules to simulate that crowded living environment in the hope that it will help to harness those thermodynamic squalls and gales to maintain quantum coherence.

But our quantum protocell remains a very needy vessel, since all its enzymes have to be preloaded on board. To make it self-sufficient we must furnish another compartment, its control room, with an artificial DNA-based genome able to encode everything it needs, together with the machinery needed to turn its quantum-level proton code into proteins. This is similar to the top-down approach utilized by Craig Venter; only our genome will be injected into a nonliving protocell. Lastly, we could even endow our protocell with a navigational system, perhaps a molecular nose to enable it to locate its food by utilizing the quantum entanglement olfactory receptor principle that we explored in chapter 5 and a molecular motor to propel itself through its primordial sea. We could even equip it with a quantum-powered navigational system, like our robin’s, which could help it to orientate itself in the laboratory-based primordial ocean.

What we have described is little more than a biological whimsy—no more real than Shakespeare’s Ariel. We have omitted a huge amount of detail and, in the interests of simplicity and intelligibility, failed to mention the colossal challenges that would face any real bottom-up synthetic biology project. Even if such a project were ever attempted, it would certainly not try to instantiate all these processes in a single step, as in our imaginary recipe above, but would instead first attempt to install the simplest or the best-understood process—maybe photosynthesis—into a protocell. This would, of course, be a major achievement in itself, and would be the perfect model system to use to investigate the role of quantum coherence in photosynthesis. Were such a feat indeed proved possible, the next steps would be to include additional components to implement greater and greater complexity, leading eventually, perhaps, to a truly artificial living cell. But this will only be possible, we predict, along the quantum route to life: life simply won’t work, we believe, without being connected to the quantum realm.

If such a project were indeed ever undertaken, then it might be possible, at last, to make new life. Such an advance could launch a truly revolutionary living technology: artificial life able to navigate the edge between the quantum and classical worlds. Artificial living cells could be engineered to serve as the bricks of truly sustainable living buildings; micro-surgeons could be constructed to repair and replace our damaged and worn tissues. The fantastic features of quantum biology that we have explored in this book, from photosynthesis to enzyme action, and from quantum noses to quantum genomes, quantum compasses and maybe even quantum brains, could all be harvested to potentially build a brave new world of quantum synthetic living organisms that could free their natural-born relatives from the drudgery of providing humanity with most of its needs.

But, perhaps even more important, the ability to make new life from scratch would finally provide biology with a reply to answer Feynman’s famous dictum that “what I can’t make, I don’t understand.” If such a project were indeed successful, then we could, finally, claim that we do at last understand life and its remarkable ability to harness the forces of chaos to sail that narrow edge between the classical and quantum worlds.

The noontide sun, call’d forth the mutinous winds,

And ’twixt the green sea and the azured vault

Set roaring war: to the dread rattling thunder …

WILLIAM SHAKESPEARE, The Tempest, ACT V, SCENE 1

*1 The term often used to describe incoherent molecular vibrations.

*2 The amplitude of the vibrations is quite small, so they do not deliver much energy.

*3 Plants have two photosystems, I and II.