How much do I want to read more? 7/10
Reading the history of quantum physics and biology can be fascinating. Not everything is clear, but this book gives the thrills of what has been overcome by the human race.
What if Quantum physics could be applied in biology?
Some migratory birds (European Robin) find their way thanks to an "inclination compass", but how can it work biologically? What if Quantum physics could explain this phenomenon?
"down in the microscopic quantum world, particles can behave in these strange ways, like doing two things at once, being able to pass through walls, or possessing spooky connections, only when no one is looking. Once they are observed, or measured in some way, they lose their weirdness and behave like the classical objects that we see around us."
How animals manage to find their way around the globe has been a mystery for centuries. We now know that they employ a variety of methods: some use solar navigation during the day and celestial navigation at night; some memorize landmarks; others can even smell their way around the planet. But the most mysterious navigational sense of all is the one possessed by the European robin: the ability to detect the direction and strength of the earth’s magnetic field, known as magnetoreception.
How, then, can that magnetic field be perceptible to the robin?
Mysteries, however small, are fascinating because there’s always the possibility that their solution may lead to a fundamental shift in our understanding of the world. Copernicus’s ponderings in the sixteenth century on a relatively minor problem concerning the geometry of the Ptolemaic geocentric model of the solar system, for instance, led him to shift the center of gravity of the entire universe away from humankind. Darwin’s obsession with the geographical distribution of animal species and the mystery of why isolated island species of finches and mockingbirds tend to be so specialized led him to propose his theory of evolution. And German physicist Max Planck’s solution to the mystery of blackbody radiation, concerning the way warm objects emit heat, led him to suggest that energy came in discrete lumps called “quanta,” leading to the birth of quantum theory in the year 1900. So, could the solution to the mystery of how birds find their way around the globe lead to a revolution in biology? The answer, bizarre as it may seem, is: yes.
A hidden spooky reality
For while compasses tell the difference between magnetic north and south poles, a robin could only distinguish between pole and equator.
The problem was that no one had a clue how any such biological inclination compass might work, because there was at that time simply no known, or even conceivable, mechanism that could account for how the angle of dip of the earth’s magnetic field could be detected within an animal’s body. The answer turned out to be within one of the most startling scientific theories of modern times, and it had to do with the strange science of quantum mechanics.
In fact, it has been estimated that over one-third of the gross domestic product of the developed world depends on applications that would simply not exist without our understanding of the mechanics of the quantum world.
The twentieth century’s quantum revolution is picking up pace in the twenty-first century and will transform our lives in unimaginable ways.
But what exactly is quantum mechanics? This is a question we will be exploring throughout this book; for a taster, we will start here with a few examples of the hidden quantum reality that underpins our lives.
We are familiar with the fact that we and all the things around us are composed of lots of tiny, discrete particles such as atoms, electrons, protons and neutrons.
You may also be aware that energy, such as light or sound, comes as waves, rather than particles. Waves are spread out, rather than particulate; and they flow through space as—well, waves, with peaks and troughs like the waves of the sea.
Quantum mechanics was born when it was discovered in the early years of the twentieth century that subatomic particles can behave like waves; and light waves can behave like particles.
Our second example is even more fundamental. Why does the sun shine?
Most people are probably aware that the sun is essentially a nuclear fusion reactor that burns hydrogen gas to release the heat and sunlight that sustain all life on earth;
but fewer people know that it wouldn’t shine at all were it not for a remarkable quantum property that allows particles to “walk through walls.”
The sun, and indeed all stars in the universe, is able to emit these vast amounts of energy because nuclei of hydrogen atoms, each composed of just a single positively charged particle called a proton, are able to fuse, and as a result to release energy in the form of the electromagnetic radiation that we call sunlight.
Two hydrogen nuclei have to be able to get very close in order to fuse; but the closer they get, the stronger the repulsive force between them becomes, as each carries a positive electric charge and “like” charges repel.
In fact, for them to get close enough to fuse, the particles have to be able to get through the subatomic equivalent of a brick wall: an apparently impenetrable energy barrier.
such as atomic nuclei, have a neat trick up their sleeve: they can easily pass through such barriers via a process called “quantum tunneling.” And it is essentially their wave–particle duality that enables them to do this.
they can also flow through objects, like the sound waves that pass through your walls when you hear your neighbor’s TV.
Of course, the air that carries sound waves doesn’t actually pass through the walls itself: it’s the vibrations in the air—sound—that cause your common wall to vibrate and push on the air in your room to transmit the same sound waves to your ear.
The third example is related, but illustrates a different and even weirder feature of the quantum world: a phenomenon called superposition whereby particles can do two—or a hundred, or a million—things at once.
This property is responsible for the fact that our universe is richly complex and interesting.
Not long after the Big Bang through which this universe came into being, space was awash with just one type of atom: the simplest in structure, hydrogen, which is made up of one positively charged proton and one negatively charged electron. It was a rather dull place, with no stars or planets and definitely no living organisms, because the elemental building blocks of everything around us, including us, consist of more than just hydrogen, including heavier elements such as carbon, oxygen and iron. Fortunately, these heavier elements were cooked up inside the hydrogen-filled stars; and their starting ingredient, a heavy hydrogen isotope called deuterium, owes its existence to a bit of quantum magic.
The first step in the recipe is the one we’ve just described, when two hydrogen nuclei, protons, get close enough together via quantum tunneling to release some of that energy that turns into the sunlight that warms our planet.
This is precisely what happens when two protons come together: a composite of two protons cannot exist and one of them will beta-decay into a neutron. The remaining proton and the newly transformed neutron can then bind together to form an object called a deuteron (the nucleus of an atom of deuterium), after which further nuclear reactions enable the building of the more complex nuclei of other elements heavier than hydrogen, from helium (with two protons and either one or two neutrons) through to carbon, nitrogen, oxygen, and so on.
The key point is that the deuteron owes its existence to its ability to exist in two states simultaneously, by virtue of quantum superposition.
It was discovered back in the late 1930s that within the deuteron these two particles are not dancing together in either one or the other of these two states, but in both states at the same time—they are in a blur of waltz and jive simultaneously—and it is this that enables them to bind together.
if the proton and neutron were performing the equivalent of either a quantum waltz or a quantum jive, then the nuclear “glue” between them would not be quite strong enough to bind them together; it is only when these two states are superimposed on top of each other—the two realities existing at the same time—that the binding force is strong enough.
So if particles couldn’t jive and waltz simultaneously our universe would have remained a soup of hydrogen gas and nothing more—no stars would shine, none of the other elements would have formed and you would not be reading these words. We exist because of the ability of protons and neutrons to behave in this quantum counterintuitive way.
no one had a clue how a biological inclination compass might work.
Why don’t all objects we see do all these weird and wonderful things that quantum particles can do? The answer is that, down in the microscopic quantum world, particles can behave in these strange ways, like doing two things at once, being able to pass through walls, or possessing spooky connections, only when no one is looking. Once they are observed, or measured in some way, they lose their weirdness and behave like the classical objects that we see around us. But then, of course, this only throws up another question: What is so special about measurement that allows it to convert quantum behavior to classical behavior? The answer to this question is crucial to our story, because measurement lies on the borderline between the quantum and classical worlds, the quantum edge, where we, as you will have guessed from the title of this book, are claiming life also lies.
To observe the quantum weirdness you either have to go to unusual places (such as the interior of the sun), peer deep into the microworld (with instruments like electron microscopes) or carefully line up the quantum particles so that they are marching in step (as happens to the spins of hydrogen nuclei within your body when it is inside an MRI scanner—until the magnet is turned off, when the spin orientation of the nuclei is randomized again, canceling out the quantum coherence once more).
Quantum phenomena such as superposition and tunneling have been detected in lots of biological phenomena, from the way plants capture sunlight to the way that all our cells make biomolecules.
Even our sense of smell or the genes that we inherit from our parents may depend on the weird quantum world.
2. What is life?
Life is remarkable.
And our robin is just one of the trillions of living organisms that are capable of performing scores of these and many other equally bewildering feats.
Another remarkable organism is, of course, you. Gaze up at the night sky and photons of light enter your eyes to be transmuted by retinal tissue into tiny electric currents that travel along your optic nerves to reach the nervous tissue of your brain.
Yet the physical feats performed by the tissue of our own bodies, however extraordinary, pale by comparison with those executed by many of our fellow living creatures.
The leafcutter ant is able to carry a load weighing thirty times its own weight, equivalent to you carrying a car on your back.
And the trap-jaw ant is able to accelerate its jaws from 0 to 230 km per hour in just 0.13 milliseconds, while a Formula 1 racing car takes about forty thousand times as long (around five seconds) to reach the same speed.
The Amazon electric eel can generate six hundred volts of potentially lethal electricity.
Birds can fly, fish can swim, worms can burrow and monkeys can swing through trees.
And, as we have already discovered, many animals, including our European robin, can find their way across thousands of miles using the earth’s magnetic field.
All living organisms have their particular skills and specialities, such as the robin’s magnetoreception or the trap-jaw ant’s speedy snapping, but there is one human organ whose performance is unparalleled. The computation skill of the gray fleshy material locked within our bony skulls exceeds that of every computer on the planet and has created the Pyramids, the General Theory of Relativity, Swan Lake, the Rig Veda, Hamlet, Ming pottery and Donald Duck. And, perhaps most remarkably of all, the human brain possesses the capacity to know that it exists.
The biggest question in science, one that is central to this book, is how the inert atoms and molecules found in rocks are transformed every day into running, jumping, flying, navigating, swimming, growing, loving, hating, lusting, fearing, thinking, laughing, crying, living stuff.
it is worth remembering that even in this age of genetic engineering and synthetic biology, nothing living has ever been made by humans entirely from nonliving materials. That our technology has so far failed to manage a transformation that is effortlessly executed by even the simplest microbe on our planet suggests that our knowledge of what it takes to make life is incomplete.
To discover why we need the hidden world of quantum mechanics to account for the amazing properties of living matter, we need first to embark on a short tour of science’s efforts to understand what is so special about life.
The “life force”
“What is it that, when present in a body, makes it living?—A soul.” Aristotle agreed with Socrates that living beings possessed souls, but he claimed that they came in different grades. The lowliest were those that inhabited plants, enabling them to grow and obtain nourishment; animal souls, one rung higher, endowed their hosts with feeling and movement; but only the human soul conferred reason and intellect.
The ancient Chinese similarly believed that living beings were animated by an incorporeal life force called Qi (pronounced “chi”) that flowed through them. The concept of a soul was later incorporated into all of the major world religions; but its nature and its connection with the body remained mysterious.
Another puzzle was mortality. Souls were generally believed to be immortal, but then why is life ephemeral? The answer that most cultures came up with was that death was accompanied by departure of the animating soul from the body.
Aristotle claimed that living creatures, unlike inanimate objects, were capable of initiating their own motion, and that in this case the cause of such motion was the creature’s soul.
Triumph of the machines
Life was different because it was moved by a spiritual soul rather than by any of those mundane mechanical forces.
But this was always an unsatisfactory explanation—equivalent to accounting for the motion of the sun, moon and stars by claiming that they were pushed around by angels.
William Harvey, who discovered that the heart was nothing more than a mechanical pump.
He accordingly concluded that “respiration is thus a very slow combustion phenomenon, very similar to that of coal.” As Descartes might have predicted, animals appeared not to be so very different from the coal-powered locomotives that were soon hauling the industrial revolution across Europe.
A molecular billiard table
The science of how heat interacts with matter is called thermodynamics;
A remarkable aspect of the science of thermodynamics is that this really is all there is to it. The orderly motion of every heat engine that has ever been built is delivered by harnessing the average motion of trillions of randomly moving atoms and molecules.
In fact, almost all of the nonbiological (physical and chemical) processes that cause change in our world are driven by thermodynamic principles. Ocean currents, violent storms, the weathering of rocks, the burning of forests and the corrosion of metals are all controlled by the inexorable forces of chaos that underpin thermodynamics. Each complex process may appear structured and orderly to us, but at their core they are all driven by random molecular motion.
Life as chaos?
In thermodynamics, the term entropy is used to describe a lack of order
Just like a bird, a fish or a human, our imaginary device is able to sustain and replicate itself by harvesting free energy from random molecular collisions.
the principle is the same: free energy harvested from random molecular collisions (and their chemical reactions) is directed to maintain a body and make a copy of that body.
Is life, then, just a branch of thermodynamics?
Peering deeper into life
He also observed plant cells, red blood cells and even spermatozoa. It was later understood that all living tissue was divided into these cellular units, the building blocks of living bodies.
Every animal presents itself as a sum of vital entities, every one of which manifests all the characteristics of life.
As living cells were studied in ever greater detail by more powerful microscopes, their internal structure was revealed to be highly complex, each with a nucleus in the center filled with chromosomes and surrounded by cytoplasm in which were embedded specialized subunits called organelles that, like our body’s organs, perform particular functions within the cell.
For example, an organelle called the mitochondrion performs respiration inside human cells, whereas the chloroplast organelle performs photosynthesis inside plant cells. Overall, the cell gives the impression of a busy miniature manufacturing plant.
But what keeps it going? What animates the cell? Initially, cells were generally thought to be filled with “vital” forces, essentially equivalent to Aristotle’s concept of the soul; and for much of the nineteenth century, the belief in vitalism—that living creatures were animated by a force absent from the nonliving—persisted. Cells were thought to be filled with a mysterious living substance called protoplasm that was described in almost mystical terms.
Increasingly, the matter of the living appeared to be made up from pretty much the same chemicals that made up the nonliving, and thereby likely to be governed by the same chemistry. Vitalism gradually gave way to mechanism.
Cells were considered to be bags of biochemicals operated by a complex chemistry, but one that was nevertheless based on the random billiard-ball-like molecular motion described by Boltzmann. Life, it was generally believed, was indeed just elaborate thermodynamics.
Except for one aspect—arguably the most important of all.
The ability of living organisms to faithfully transmit the instructions to make another of themselves—whether a robin, rhododendron or a person—was, for centuries, profoundly puzzling.
His observations led him to propose that traits such as flower color or pea shape were controlled by heritable “factors” that could be transmitted, unchanged, from one generation to the next.
The discovery of the structure of DNA provided a mechanistic key that unlocked the mystery of genes. Genes are chemicals and chemistry is just thermodynamics;
Life’s curious grin
Yet every living cell in your body is continually synthesizing thousands of distinct biochemicals within a reaction chamber filled with just a few millionths of a microliter of fluid. How do all those diverse reactions proceed concurrently? And how is all this molecular action orchestrated within a microscopic cell? These questions are the focus of the new science of systems biology; but it is fair to say that the answers remain mysterious!
Life is different. No one has ever discovered a condition that favors the direction: dead cell → live cell. This was of course the puzzle that prompted our ancestors to come up with the idea of a soul. We no longer believe that a cell possesses any kind of soul; but what is it then that is irrevocably lost when a cell or a person dies?
The Nobel Prize–winning physicist Richard Feynman is credited with insisting that “what we can’t make, we don’t understand.” By this definition, we do not understand life because we have not yet managed to make it.
So why is it that we are still unable to perform a trick that is effortlessly executed by trillions of the lowliest microbes every second?
Are we missing an ingredient? This is the question that a famous physicist, Erwin Schrödinger, pondered more than seventy years ago; and his very surprising answer is central to the theme of this book.
The quantum revolution
The explosion of scientific knowledge during the Enlightenment of the eighteenth and nineteenth centuries produced Newtonian mechanics, electromagnetism and thermodynamics, and showed that together these three areas of physics successfully described the motion and behavior of all macroscopic everyday objects and phenomena in our world, from cannonballs to clocks, from storms to steam trains, from pendulums to planets.
But in the late nineteenth and early twentieth centuries, when physicists turned their attention to the microscopic constituents of matter—atoms and molecules—they discovered that the familiar laws no longer applied. Physics needed a revolution.
The problem was that the wave theory could not explain the way certain hot objects radiate energy. So Planck proposed the radical idea that the matter in the walls of these hot bodies vibrated at certain discrete frequencies, which had the consequence that the heat energy was only radiated in tiny discrete lumps, or “quanta,” that could not be subdivided.
His theory suggested that energy, instead of flowing out of matter like water pouring continuously from a tap, came out as a collection of separate, indivisible packages—as if from a slowly dripping tap.
But there was also plenty of evidence that light behaves as a spread-out and continuous wave. So how can light be both lumpy and wavy? It didn’t seem to make sense at the time; at least, not within the framework of classical science.
According to standard electromagnetic theory, the negatively charged electrons would constantly emit light energy as they orbited the positively charged nucleus. In doing so, they would lose energy and very quickly (within a thousand billionth of a second) spiral inward toward the nucleus, causing the atom to collapse. But electrons don’t do this. So what was their trick?
To explain the stability of atoms, Bohr proposed that electrons aren’t free to occupy any orbit around the nucleus, but instead only certain fixed (“quantized”) orbits. An electron can only drop to the next lower orbit by emitting a lump, or quantum, of electromagnetic energy (a photon) of exactly the same value as the difference in energies between the two orbits involved. Likewise, it can only jump to a higher orbit by absorbing a photon of the appropriate energy.
For instance, Heisenberg argued not only that we could not say exactly where an atomic electron was if we weren’t measuring it, but that the electron itself did not have a definite location because it was spread out in a fuzzy, unknowable way.
Heisenberg was forced to conclude that the atomic world is a ghostly, insubstantial place that crystallizes into sharp existence only when we set up a measuring device to interact with it.
Schrödinger equation, which describes not the way a particle moves but the way that a wave evolves. It suggested that rather than an electron being a fuzzy particle in the atom, with an unknowable position as it orbits the nucleus, it is instead a wave spread throughout the atom.
Unlike Heisenberg, who believed that it is impossible to have a picture of an electron at all when we are not measuring it, Schrödinger preferred to think of it as a real physical wave when we aren’t looking at it, which “collapses” to a discrete particle whenever we do look.
Schrödinger’s wave function
When we wish to describe the motion of everyday objects, whether cannonballs or steam trains or planets, each one composed of trillions of particles, we solve the problem using a set of mathematical equations that date back to the work of Isaac Newton. But if the system we are describing resides in the quantum world, then we have to use Schrödinger’s equation instead.
And here lies the profound difference between the two approaches, for in our Newtonian world the solution of an equation of motion is a number, or a set of numbers, that define(s) the precise location of an object at a given moment in time. In the quantum world, the solution of the Schrödinger equation is a mathematical quantity called the wave function, which does not tell us the precise location of, say, an electron at a particular moment in time, but instead provides a whole set of numbers that describe the likelihood of the electron’s being found at different locations in space if we were to look for it there.
But unlike a classical object that always occupies a definite position in space, an electron could be in multiple places at once until the moment it is measured.
It is important to realize, however, that these quantum probabilities do not represent some deficiency in our knowledge that could be cured by obtaining more information; rather, they are a fundamental feature of the natural world at this microscopic scale.
Likewise, if the electron is detected in a certain location then its wave function is instantly altered. At the moment of detection there will be zero probability of finding it anywhere else.
Instead, all we have to describe it is the wave function, which is everywhere at once. Only through the act of looking (carrying out a measurement) can we “force” the electron to become a localized particle.
By 1927, thanks to the efforts of Heisenberg, Schrödinger and others, the mathematical underpinnings of quantum mechanics were essentially complete. Today, they constitute the foundation on which much of physics and chemistry are built and give us a remarkably complete picture of the building blocks of the entire universe. Indeed, without the explanatory power of quantum mechanics in describing how everything fits together, much of our modern technological world would simply not be possible.
The early quantum biologists
But life, he argued, was different, because it was ruled by a very few molecules within the Steuerungszentrum that have a dictatorial influence, such that quantum-level events that govern their motion, such as Heisenberg’s Uncertainty Principle, are amplified to influence the entire organism.
Order all the way down
The problem that intrigued Schrödinger was the mysterious process of heredity. You may recall that at this time, in the first half of the twentieth century, scientists knew that genes were inherited by one generation from the previous, but not what genes were made of or how they worked. What laws, Schrödinger wondered, provided heredity with its high level of fidelity? In other words, how could identical copies of genes be passed virtually unchanged from one generation to the next?
statistical laws, which means they are only true on average, and only reliable because they involve very large numbers of particles interacting.
Thermodynamics works like this: it is the average behavior of lots of molecules that is predictable, not the behavior of individual molecules. Schrödinger pointed out that statistical laws, such as those of thermodynamics, cease to accurately describe systems composed of just a small number of particles.
How does disorderly motion generate orderly laws?
The important point is that the singular object that is the balloon strictly obeys the gas law because the orderly motion of its single continuous elastic surface arises from the disorderly motions of very large numbers of particles, generating, as Schrödinger put it, order from disorder.
Schrödinger argued that it is not only the gas laws that derive their accuracy from the statistical properties of large numbers; all the laws of classical physics and chemistry—including the laws governing the dynamics of fluids or chemical reactions—are based on this “averaging of large numbers” or “order from disorder” principle.
Schrödinger went further than simply observing that the statistical laws of classical physics could not be relied on at the microscopic level: he quantified the decline in accuracy, calculating that the magnitude of deviations from those laws is inversely proportional to the square root of the number of particles involved.
But what about life? Can its orderly behavior, such as its laws of heredity, be accounted for by statistical laws? When Schrödinger pondered this question he concluded that the “order from disorder” principle that underpinned thermodynamics could not govern life—because, as he saw it, at least some of the tiniest biological machines are just too small to be governed by classical laws.
life is different from inanimate objects because relatively small numbers of highly ordered particles, such as those inside a gene or the avian compass, can make a difference to an entire organism.
This is what Jordan termed amplification and Schrödinger called order from order.
The color of your eyes, the shape of your nose, aspects of your character, your level of intelligence and even your propensity to disease have in fact all been determined by precisely forty-six highly ordered supermolecules: the DNA chromosomes you inherited from your parents.
No inanimate macroscopic object in the known universe has this sensitivity to the detailed structure of matter at its most fundamental level—a level where quantum mechanical rather than classical laws reign. Schrödinger argued that this is what makes life so special.