Symmetries Obeyed and Broken
Lucifer's Legacy: The Meaning of Asymmetry. Frank Close. 259 pp. Oxford University Press, 2000. $27.50.
Antimatter: The Ultimate Mirror. Gordon Fraser. 213 pp. Cambridge University Press, 2000. $24.95.
Popularization has its perils. It is hard enough to recount complex theories and experiments clearly, harder still to make them accessible and attractive, and hardest of all to rouse the reader from unreflective passivity. As a reader, I may at first be content only to gaze at the mysteries of science with mute admiration. In the end, though, if I cannot begin to think about these mysteries on my own, I may lose interest and turn away in despair or disgust. Or I may feel cheated, as if I had come to a great banquet and read the enticing menu but had come away unfed.
Like other popular works about science, these two books confront a hunger in readers for a deeper understanding of science and must be judged in part on how well they satisfy it. They both treat the symmetries of nature, but they approach them differently.
Lucifer's Legacy concentrates on the importance of asymmetry. (The title refers to the author's encounter with a striking violation of the formal symmetry in the Tuileries Gardens in Paris, a statue of Lucifer whose fallen head seems to spoil the garden's perfect design.) Beginning with the symmetries of the human body and brain, Frank Close, a physicist and broadcaster, discusses the left- and right-handedness of molecules and the important asymmetries of organic compounds crucial to life. His examples are fascinating and often fresh. He makes only a few missteps (the last chord of Bach's St. Matthew Passion is not simply unresolved, nor does the color range of visible light span the interval of even one octave in frequency, as he says).
He tells the story of modern physics from the discovery of x-rays to the symmetries obeyed and broken in the atomic and nuclear realms. Throughout, his presentation is lively and charming. One can readily imagine him linking several children hand to hand to form a human battery, as he describes having done when he lectured in 1993 in the famous series of Christmas talks at London's Royal Institution.
Although Close's examples are sometimes homey, they are not condescending, because he engages the reader in a real process of thought. For instance, he pauses to wonder about ordinary mirrors. Do they really reverse right and left? What about up and down? We are invited, directly and unpretentiously, to think it through with him, and he helps us consider the options without foreclosing our own reflections. When you think it through, with his guidance, the answer is surprising and rather wonderful. These are the finest moments in the book, and readers will come away not merely having heard about physics but having thought about it for themselves.
Take the image of a mirror, especially antimatter as "the ultimate mirror" of matter. Though attractive, this analogy remains somewhat confusing. Fraser mentions in passing that mirrors reverse left and right, whereas Close leads us to question that commonplace. How can we think about antiparticles as mirror images of particles if we can't get straight what a mirror does in the first place? This is especially true since it emerges that the antimatter "mirror" changes what it reflects, for nature can distinguish between left and right.
If the reader is to follow such strange ideas, many questions need to be raised and addressed more carefully. For instance, how could gravity ever become a repulsive force? How could cosmic inflation proceed faster than the speed of light, as Fraser tells us it does? Since the author does not help us think about such questions, we can merely admire the incomprehensible exploits of scientists that he describes, without much clue as to how one could ever make sense of them.
Fraser does provide some engaging details that enrich his exposition, and one is grateful that he includes such figures as Hans Dehmelt, the thoughtful "master trapper" of matter and antimatter, who deserves far greater renown. Yet much of Fraser's history is schematic and unquestioning. Sometimes this simplified approach leads him to misrepresent history. Fraser gives an account of the origins of quantum theory in terms of reaction to a presumed "ultraviolet catastrophe." In this, he is following the regrettable precedent of many scientific textbooks that give this version. The physicist and historian Martin J. Klein long ago showed that Max Planck knew of no such "catastrophe" when he made his first steps toward the quantum in 1900. That "catastrophe" was only formulated years later, then taken up by textbooks to make the course of history seem simpler.
Elsewhere, Fraser implies that followers of "the powerful Socrates" were skeptical of atomism because it clashed with his "dogma," unaccountably ignoring that thinker's oft-reiterated claim to know nothing, to promulgate no dogma. Questions about atomic theory are not just dogmatic objections. Also, Fraser's claim that the atomic theory was "ready for the textbooks" in 1860 is based on a simplistic notion of scientific truth and ignores the fact that a number of distinguished scientists doubted the reality of atoms well into the 20th century.
Fraser's historical account of more recent figures seems more accurate, as if he had been careful to consult scientific advisers to avoid gaffes. One wishes he had been as assiduous in exploring what thoughtful historians of science could have taught him.
More fundamentally, Fraser is not clear about the significance of asymmetry. For instance, he uses the image of the Taj Mahal to illustrate "perfect but nevertheless superficial symmetry" and to serve as an analogy: "Like the grand plan of the Taj Mahal, perhaps antimatter is there to ensure an overall superficial symmetry which we can no longer see from our viewpoint." This is deeply puzzling, especially the word "superficial," which suggests that the symmetry should be obvious or apparent. So far as is now known, the universe apparently does not contain equal amounts of matter and antimatter, and in that way is not symmetrical. Then what has happened to Fraser's symmetric image of the Taj Mahal?
In contrast, Close emphasizes the crucial importance of deviations from symmetry, especially in the development of life. Unlike Fraser, who simply identifies beauty and symmetry, Close notes that deviations from symmetry are critical in visual design. A Persian rug, it is said, always includes a telling "flaw," enhancing its beauty while acknowledging the limits of human art.
A popular treatment can also be thoughtful. A good reporter probes and asks hard questions to help his readers delve deeper. Perhaps because he is also a physicist, Close is readier to ask such questions, and this gives his book added value. Unfortunately, both books lack substantial notes giving sources or suggestions for further reading, leaving readers without guidance if they wish to learn more. In their different ways, these books show how important it is for readers to be shown the central questions and encouraged to think for themselves.
Lucifer's LegacyThe Meaning of Asymmetry
By FRANK CLOSEOxford University Press
By FRANK CLOSEOxford University Press
Lucifer
`Headless body found in topless bar'
(USA newspaper headline)
The world is an asymmetrical place full of asymmetrical beings. If the Creation had been perfect, and its symmetry had remained unblemished, nothing that we now know would ever have been. There would have been no you to read this book, nor me to have written it; there would have been no Paris in the spring, and no Tuileries Gardens. So I would not have come across the headless body—the chance event that started me wondering on the accident, or design, that has created life out of arid equations.
Lest you mistake this for a seamy pot-boiler, or even Hercule Poirot-style murder mystery, I should make clear at the outset that the body in question was made of stone, its head lying in the gravel at the base of a plinth which bore the legend `Lucifer'. Had it been other than in the Tuileries I would probably have passed by without giving a second glance, but the gardens are beautiful, laid out with mathematical precision. I paused and looked again at headless Lucifer. Its disfigured presence in the midst of an otherwise all pervading perfection was as profound as the unresolved chord that ends Bach's St Matthew Passion and seemed like a metaphor for existence.
The spring day had started slowly as I had come to Paris by train from London. The carriages had meandered through southern England, as if to give the passengers time to appreciate the picture postcard views of Kent, before speeding through the featureless landscapes of northern France, impatient for the graceful architecture of Paris, among which is one of the most remarkable perspectives in Europe. From the midpoint of the Arc de Triomphe the line of sight along the Champs Elysées leads first to the obelisk at the centre of the Place de la Concorde and then runs the length of the Tuileries Gardens to the open arms of the Louvre. Where this line passes through the Tuileries it has been used like a mirror such that with draughtsmanlike precision the two halves of the gardens are perfect reflections of one another (Fig. 1.1).
To experience the symmetry to the full, first stand at the western end in the Place de la Concorde looking in the direction of the Louvre at the far end of the Tuileries. Within the park and a hundred metres to your right is the Orangerie, a hothouse erected by Napoleon III and now used for art shows; its mirror image, the same distance on your left, is the Musée du Jeu de Paume, Napoleon's tennis court. Identical mirrored paths connect the two buildings to your position at the park's entrance. On your immediate left you will see a high stone wall, curved with its concave side towards you; to the right of you is another wall, its arc a perfect mirror of its partner. The pair are a miniature imitation of the curved collonades that caress your arrival before the entrance of St Peter's in Rome. Whereas statues of angels decorate Michael-angelo's creation, the entrance to the Tuileries holds sinister statues of philosophers, gods, and dead Frenchmen in its embrace; to your left and to your right the guardians stand in perfect symmetry. The effect though is similar. The pair of symmetric concave curves are like a mother's arms taking her child; they welcome and encourage you to enter within.
The central avenue leads proudly from the far side of the curve, diametrically opposite you. This gravel carriageway defines the axis of the imaginary mirror, identical trees and flower-beds bordering it to left and right. Were you to rest briefly on one of the benches alongside the path and survey the beauty of the gardens, you would find the view obscured by a corresponding bench across the way. To every statue on one side there is a statue on the other, to every tree a tree, to every flower garden on the north side there is another planted at the same distance to the south. A water fountain sprays from the mouth of a nymph who is gazing soulfully at its clone, forever separated by twice the distance to the centre line of the park.
And so it went on until I saw the headless devil twenty metres down a side path. I knew that behind me, as yet unseen, would be a mirror image of this path that would lead to a correspondingly positioned plinth and fiendish statue. I half expected that this too would be broken, so preserving the symmetry of the park, but when I turned and looked I saw that its diabolic twin grinned from its plinth as it had done since its creation. In the entire gardens the designer symmetry was perfect with the sole exception of headless Lucifer.
The symmetry of the Tuileries Gardens and its interruption by the disfigured devil are metaphors for our grander perceptions of the natural world. Symmetry is fascinating and appealing; scientists seek it in their data and incorporate it in their theories, ironically even when there is no immediate evidence for it. Perhaps the most arcane example of this concerns the nature of matter and the fabric of existence embodied in the current cosmophysical description of Creation.
There is direct evidence that the stuff of which we are made is but half of a symmetric whole. Scientists speak casually of antimatter, the faithful opposite of matter, the symmetry so perfect that when any particle of matter meets its mirror antiparticle, mutual annihilation occurs. It is the romance of this mutual suicide pact and the accompanying burst of energy that has made antimatter so beloved by science fiction writers and the chosen power source of the Starship Enterprise in `Star Trek'. Physicists at CERN, the European Centre for Particle Physics in Geneva, can even watch this happen, confirming time and again the vulnerability of matter for antimatter. They also see the converse, where a large enough concentration of energy can coagulate into the two forms of substance: matter, as we know it, and its mirror image, antimatter.
So precisely balanced are these twins, so symmetrical their behaviour, that it has become the dogma of the new theology (or at least the one that is most popular among cosmologists) that the two were made equally in the Creation. In the beginning, they say, there was no time, no space, no substance of any kind; this is a modern version of `there was darkness on the face of the void'. Then came a burst of energy: `let there be light and there was light'. Where did it come from? You may well ask. I don't know and nor, in my opinion, does any scientist with certainty. Questions concerning existence `before' this singular happening are wracked with philosophical debate as to whether they are even meaningful: what means `before' if there was no space nor time? Some popular descriptions seem content to portray a will-o'-the-wisp universe which erupted as a quantum fluctuation out of nothing. Maybe it did, but if so then I would feel compelled to ask why it bothered. Questions relating to the `spontaneous' appearance of that first flash of searing heat that we loosely call the Big Bang begin with `why' and, as such, are beyond (current) experimental scientific enquiry.
Much of the sometimes confused debate about science `versus' religion fails to distinguish between the `why?' and `how?' varieties of question. Why the void erupted into light is for others to debate; how our present material universe emerged from that light of creation is within science's province. Answers come from experiment—a crucial feature that distinguishes our modern scientific saga from other myths. Thus the CERN experiments on the production of the simplest particles and antiparticles out of radiant energy have inspired the current theories on the emergence of matter and antimatter during the Big Bang. A perfect Creation, with its symmetry untainted, would have led to matter and antimatter in precise balance and a mutual annihilation when in the very next instant they recombined: a precisely symmetrical universe would have vanished as soon as it had appeared. Such a uniform cosmic soup could hardly have led to the asymmetrical universe that we are a part of today where antimatter appears to be all but absent.
The current theory is that Creation was barely completed before something interceded; the perfection where the essence of every atom of substance had been counterbalanced by a precise antipartner was lost forever. This act degraded the symmetry between matter and antimatter, with the result that after the great annihilation, a small proportion of the matter was left over. Those remnants are what have formed us and everything around us as far as we can see. We are the material rump of what must have been an even grander Creation.
The flawed opus is what we are left with and, but for which, we would not be. Thus did the broken statue of Lucifer, spoiling the balance of the Tuileries Gardens, so brusquely remind me that the real world is full of asymmetrical features. The sly smirk on the Devil's face seemed to be one of victory as if humans and even the existence of the entire material universe are permanent legacies of blemishes introduced somehow during the Creation.
This disruption to the great design set me wondering about the multitudes of natural asymmetries that seem to have been necessary for human life to have emerged. Matter defeating antimatter was a necessary step for there to be anything at all, but this alone was not enough. Had that been the end of it, the material universe would have been merely a bland plasma of particles with no periodic table of the elements needed for life nor a solid earth to be the factory for its construction.
The simplest element, hydrogen, formed first, and the force of gravity collected it into the vast clumps that are stars, such as our sun. Had gravity been the only force at work, that would have been the end of the story: elemental pieces of hydrogen, falling in on one another, swirling into the vortices of black holes, and extinction. A simple implosive story perhaps, but with no sentient beings to record it. However, nature differentiated other forces that can transmute the elements, producing the profound version of a material universe that we are privileged to have evolved in.
With hydrogen as the fuel, the stellar cooker first produces helium and then mixes the heavier elements such as carbon, nitrogen, and oxygen—so necessary for life. The sun has been in the first stage, burning hydrogen, for five thousand million years and radiating sunlight across a hundred million miles of space to our planet throughout that time. It is this warmth that has energized the chemical and biological processes of life, which have in turn needed that vast timespan to evolve complex human systems from primeval DNA.
Here, once more, asymmetry has been necessary. The warmth from the sun, the radiant glory of the electromagnetic force, has vibrated all the way from that distant ball of fire, whereas the force involved in the transmutation of hydrogen in the sun has its sphere of influence smaller than the dimensions of an individual atomic particle. Its strength is much weaker than that of the electromagnetic force. This enfeeblement is what has enabled the sun to survive; had it not been like this, had the force driving the solar furnace been as powerful as the electromagnetic force, all of the solar fuel would have been exhausted within five hundred thousand years—far too brief a time for life on earth, or anywhere, to have emerged. This separation of the electromagnetic force and its aptly named `weak' sibling is but one of the critical asymmetries that has been necessary for our existence.
The structure of the atomic elements also is lopsided. Biology, chemistry, and life are the result of electric currents—coursing through the nervous system, changing food into energy, building our bodies and the very fabric of the planet. It is the journeying of the little electrons, the carriers of electrical charge, that determine everything that we experience. The individual atoms consist of these negatively charged electrons swarming around a static, bulky, positively charged nucleus. All but one of the two thousand parts of the mass of an atom reside in this central nucleus, while the tiny electrons flow from one atom to another; liberated as current they flow through wires and power modern industry; agitated by electric fields they radiate electromagnetic waves. It is these negative charges that communicate and drive the biochemical processes in living things while the positives, too heavy to be easily stirred, tend to stay at home and form the templates of solidity. This asymmetry in mass is crucial for the structure of materials.
However, this alone appears to be insufficient for life. Life appears to thrive on mirror asymmetry, a distinction between left and right in the basic structures of organic molecules. Let me expand on this now, as it will be central to our story.
The positive seeds with their negative captives form atoms and molecules. There are simple ones such as water; more complex examples such as amino acids, proteins, and DNA; and others created by human ingenuity, such as plastics, ceramics, and drugs. Most of these have shapes that differ from their mirror images. Superficially identical in all respects but for the interchange of left and right, one might have reasonably expected that both forms would be equally abundant in nature. However, it is not so; life is mirror asymmetric. This is not simply a matter of there being more right handers than left, or even of our heart and stomach being found, usually, on our left side. The amino acids and molecules of life in one form have the ability to know that they exist and to be cogniscent of the universe; their mirror images are inorganic, lifeless. Life chooses one form while the mirror image is rejected. The body may happily digest a substance in one of the two mirror forms as food while excreting its mirror image unused, or worse, be poisoned by it. How and why has this mirror asymmetry emerged?
The deeper one looks, the more asymmetry becomes apparent and seemingly necessary for anything `useful' to have emerged. Without asymmetry and structure, the universe would have been bland. Have we convinced ourselves that the Creation was perfect on nothing more than wish fulfilment, as evidence of imperfection and asymmetry is all around us and even within us? I wonder whether the multitudes of asymmetries are the proof that we are the end products of chance and that philosophers and scientists have created a quasi-religious parable of symmetry that is obscuring the real explanation. Or was there indeed a perfect symmetrical scheme which included some wonderful single ingredient, yet to be identified, from which all the asymmetries for life have spontaneously emerged?
The focus of much current research is to understand how nature hides symmetry, producing structured patterns out of underlying uniformity. The quest to find the answer and possibly the singular source of all asymmetry, the reason for form and existence, began in the Tuileries Gardens and culminated in this book.
The story divides effectively into three parts. First, the mystery is introduced in Chapters 2 to 4. Then, in Chapters 5 to 7, we meet the forensic tools that have been central in solving it. These chapters tell of the discoveries, a hundred years ago, of X-rays, radioactivity, and of the structure of the atom from which have emerged the modern profound insights into the origins and evolution of life and the universe. These three chapters are self-contained, primarily of historic interest and provide a background for the main story. Chapters 8 to 13 put these forensic tools to work to reveal what scientists currently believe to be the source of structure and asymmetry in nature, and describe how they are planning to complete the solution during the first years of this new century.