A short history of nearly everything

8 EINSTEIN’S UNIVERSE

AS THE NINETEENTH century drew to a close, scientists could reflect with satisfaction that they had pinned down most of the mysteries of the physical world: electricity, magnetism, gases, optics, acoustics, kinetics, and statistical mechanics, to name just a few, all had fallen into order before them. They had discovered the X ray, the cathode ray, the electron, and radioactivity, invented the ohm, the watt, the Kelvin, the joule, the amp, and the little erg.

If a thing could be oscillated, accelerated, perturbed, distilled, combined, weighed, or made gaseous they had done it, and in the process produced a body of universal laws so weighty and majestic that we still tend to write them out in capitals: the Electromagnetic Field Theory of Light, Richter’s Law of Reciprocal Proportions, Charles’s Law of Gases, the Law of Combining Volumes, the Zeroth Law, the Valence Concept, the Laws of Mass Actions, and others beyond counting. The whole world clanged and chuffed with the machinery and instruments that their ingenuity had produced. Many wise people believed that there was nothing much left for science to do.

In 1875, when a young German in Kiel named Max Planck was deciding whether to devote his life to mathematics or to physics, he was urged most heartily not to choose physics because the breakthroughs had all been made there. The coming century, he was assured, would be one of consolidation and refinement, not revolution. Planck didn’t listen. He studied theoretical physics and threw himself body and soul into work on entropy, a process at the heart of thermodynamics, which seemed to hold much promise for an ambitious young man.[15] In 1891 he produced his results and learned to his dismay that the important work on entropy had in fact been done already, in this instance by a retiring scholar at Yale University named J. Willard Gibbs.

Gibbs is perhaps the most brilliant person that most people have never heard of. Modest to the point of near invisibility, he passed virtually the whole of his life, apart from three years spent studying in Europe, within a three-block area bounded by his house and the Yale campus in New Haven, Connecticut. For his first ten years at Yale he didn’t even bother to draw a salary. (He had independent means.) From 1871, when he joined the university as a professor, to his death in 1903, his courses attracted an average of slightly over one student a semester. His written work was difficult to follow and employed a private form of notation that many found incomprehensible. But buried among his arcane formulations were insights of the loftiest brilliance.

In 1875-78, Gibbs produced a series of papers, collectively titled On the Equilibrium of Heterogeneous Substances, that dazzlingly elucidated the thermodynamic principles of, well, nearly everything-“gases, mixtures, surfaces, solids, phase changes . . . chemical reactions, electrochemical cells, sedimentation, and osmosis,” to quote William H. Cropper. In essence what Gibbs did was show that thermodynamics didn’t apply simply to heat and energy at the sort of large and noisy scale of the steam engine, but was also present and influential at the atomic level of chemical reactions. Gibbs’s Equilibrium has been called “the Principia of thermodynamics,” but for reasons that defy speculation Gibbs chose to publish these landmark observations in the Transactions of the Connecticut Academy of Arts and Sciences, a journal that managed to be obscure even in Connecticut, which is why Planck did not hear of him until too late.

Undaunted-well, perhaps mildly daunted-Planck turned to other matters.[16] We shall turn to these ourselves in a moment, but first we must make a slight (but relevant!) detour to Cleveland, Ohio, and an institution then known as the Case School of Applied Science. There, in the 1880s, a physicist of early middle years named Albert Michelson, assisted by his friend the chemist Edward Morley, embarked on a series of experiments that produced curious and disturbing results that would have great ramifications for much of what followed.

What Michelson and Morley did, without actually intending to, was undermine a longstanding belief in something called the luminiferous ether, a stable, invisible, weightless, frictionless, and unfortunately wholly imaginary medium that was thought to permeate the universe. Conceived by Descartes, embraced by Newton, and venerated by nearly everyone ever since, the ether held a position of absolute centrality in nineteenth-century physics as a way of explaining how light traveled across the emptiness of space. It was especially needed in the 1800s because light and electromagnetism were now seen as waves, which is to say types of vibrations. Vibrations must occur in something; hence the need for, and lasting devotion to, an ether. As late as 1909, the great British physicist J. J. Thomson was insisting: “The ether is not a fantastic creation of the speculative philosopher; it is as essential to us as the air we breathe”-this more than four years after it was pretty incontestably established that it didn’t exist. People, in short, were really attached to the ether.

If you needed to illustrate the idea of nineteenth-century America as a land of opportunity, you could hardly improve on the life of Albert Michelson. Born in 1852 on the German-Polish border to a family of poor Jewish merchants, he came to the United States with his family as an infant and grew up in a mining camp in California’s gold rush country, where his father ran a dry goods business. Too poor to pay for college, he traveled to Washington, D.C., and took to loitering by the front door of the White House so that he could fall in beside President Ulysses S. Grant when the President emerged for his daily constitutional. (It was clearly a more innocent age.) In the course of these walks, Michelson so ingratiated himself to the President that Grant agreed to secure for him a free place at the U.S. Naval Academy. It was there that Michelson learned his physics.

Ten years later, by now a professor at the Case School in Cleveland, Michelson became interested in trying to measure something called the ether drift-a kind of head wind produced by moving objects as they plowed through space. One of the predictions of Newtonian physics was that the speed of light as it pushed through the ether should vary with respect to an observer depending on whether the observer was moving toward the source of light or away from it, but no one had figured out a way to measure this. It occurred to Michelson that for half the year the Earth is traveling toward the Sun and for half the year it is moving away from it, and he reasoned that if you took careful enough measurements at opposite seasons and compared light’s travel time between the two, you would have your answer.

Michelson talked Alexander Graham Bell, newly enriched inventor of the telephone, into providing the funds to build an ingenious and sensitive instrument of Michelson’s own devising called an interferometer, which could measure the velocity of light with great precision. Then, assisted by the genial but shadowy Morley, Michelson embarked on years of fastidious measurements. The work was delicate and exhausting, and had to be suspended for a time to permit Michelson a brief but comprehensive nervous breakdown, but by 1887 they had their results. They were not at all what the two scientists had expected to find.

As Caltech astrophysicist Kip S. Thorne has written: “The speed of light turned out to be the same in all directions and at all seasons.” It was the first hint in two hundred years-in exactly two hundred years, in fact-that Newton’s laws might not apply all the time everywhere. The Michelson-Morley outcome became, in the words of William H. Cropper, “probably the most famous negative result in the history of physics.” Michelson was awarded a Nobel Prize in physics for the work-the first American so honored-but not for twenty years. Meanwhile, the Michelson-Morley experiments would hover unpleasantly, like a musty smell, in the background of scientific thought.

Remarkably, and despite his findings, when the twentieth century dawned Michelson counted himself among those who believed that the work of science was nearly at an end, with “only a few turrets and pinnacles to be added, a few roof bosses to be carved,” in the words of a writer in Nature.

In fact, of course, the world was about to enter a century of science where many people wouldn’t understand anything and none would understand everything. Scientists would soon find themselves adrift in a bewildering realm of particles and antiparticles, where things pop in and out of existence in spans of time that make nanoseconds look plodding and uneventful, where everything is strange. Science was moving from a world of macrophysics, where objects could be seen and held and measured, to one of microphysics, where events transpire with unimaginable swiftness on scales far below the limits of imagining. We were about to enter the quantum age, and the first person to push on the door was the so-far unfortunate Max Planck.

In 1900, now a theoretical physicist at the University of Berlin and at the somewhat advanced age of forty-two, Planck unveiled a new “quantum theory,” which posited that energy is not a continuous thing like flowing water but comes in individualized packets, which he called quanta. This was a novel concept, and a good one. In the short term it would help to provide a solution to the puzzle of the Michelson-Morley experiments in that it demonstrated that light needn’t be a wave after all. In the longer term it would lay the foundation for the whole of modern physics. It was, at all events, the first clue that the world was about to change.

But the landmark event-the dawn of a new age-came in 1905, when there appeared in the German physics journal Annalen der Physik a series of papers by a young Swiss bureaucrat who had no university affiliation, no access to a laboratory, and the regular use of no library greater than that of the national patent office in Bern, where he was employed as a technical examiner third class. (An application to be promoted to technical examiner second class had recently been rejected.)

His name was Albert Einstein, and in that one eventful year he submitted to Annalen der Physik five papers, of which three, according to C. P. Snow, “were among the greatest in the history of physics”-one examining the photoelectric effect by means of Planck’s new quantum theory, one on the behavior of small particles in suspension (what is known as Brownian motion), and one outlining a special theory of relativity.

The first won its author a Nobel Prize and explained the nature of light (and also helped to make television possible, among other things).[17] The second provided proof that atoms do indeed exist-a fact that had, surprisingly, been in some dispute. The third merely changed the world.

Einstein was born in Ulm, in southern Germany, in 1879, but grew up in Munich. Little in his early life suggested the greatness to come. Famously he didn’t learn to speak until he was three. In the 1890s, his father’s electrical business failing, the family moved to Milan, but Albert, by now a teenager, went to Switzerland to continue his education-though he failed his college entrance exams on the first try. In 1896 he gave up his German citizenship to avoid military conscription and entered the Zurich Polytechnic Institute on a four-year course designed to churn out high school science teachers. He was a bright but not outstanding student.

In 1900 he graduated and within a few months was beginning to contribute papers to Annalen der Physik. His very first paper, on the physics of fluids in drinking straws (of all things), appeared in the same issue as Planck’s quantum theory. From 1902 to 1904 he produced a series of papers on statistical mechanics only to discover that the quietly productive J. Willard Gibbs in Connecticut had done that work as well, in his Elementary Principles of Statistical Mechanics of 1901.

At the same time he had fallen in love with a fellow student, a Hungarian named Mileva Maric. In 1901 they had a child out of wedlock, a daughter, who was discreetly put up for adoption. Einstein never saw his child. Two years later, he and Maric were married. In between these events, in 1902, Einstein took a job with the Swiss patent office, where he stayed for the next seven years. He enjoyed the work: it was challenging enough to engage his mind, but not so challenging as to distract him from his physics. This was the background against which he produced the special theory of relativity in 1905.

Called “On the Electrodynamics of Moving Bodies,” it is one of the most extraordinary scientific papers ever published, as much for how it was presented as for what it said. It had no footnotes or citations, contained almost no mathematics, made no mention of any work that had influenced or preceded it, and acknowledged the help of just one individual, a colleague at the patent office named Michele Besso. It was, wrote C. P. Snow, as if Einstein “had reached the conclusions by pure thought, unaided, without listening to the opinions of others. To a surprisingly large extent, that is precisely what he had done.”

His famous equation, E=mc², did not appear with the paper, but came in a brief supplement that followed a few months later. As you will recall from school days, E in the equation stands for energy, m for mass, and c² for the speed of light squared.

In simplest terms, what the equation says is that mass and energy have an equivalence. They are two forms of the same thing: energy is liberated matter; matter is energy waiting to happen. Since c² (the speed of light times itself) is a truly enormous number, what the equation is saying is that there is a huge amount-a really huge amount-of energy bound up in every material thing.[18]

You may not feel outstandingly robust, but if you are an average-sized adult you will contain within your modest frame no less than 7 x 10¹⁸ joules of potential energy-enough to explode with the force of thirty very large hydrogen bombs, assuming you knew how to liberate it and really wished to make a point. Everything has this kind of energy trapped within it. We’re just not very good at getting it out. Even a uranium bomb-the most energetic thing we have produced yet-releases less than 1 percent of the energy it could release if only we were more cunning.

Among much else, Einstein’s theory explained how radiation worked: how a lump of uranium could throw out constant streams of high-level energy without melting away like an ice cube. (It could do it by converting mass to energy extremely efficiently à la E=mc².) It explained how stars could burn for billions of years without racing through their fuel. (Ditto.) At a stroke, in a simple formula, Einstein endowed geologists and astronomers with the luxury of billions of years. Above all, the special theory showed that the speed of light was constant and supreme. Nothing could overtake it. It brought light (no pun intended, exactly) to the very heart of our understanding of the nature of the universe. Not incidentally, it also solved the problem of the luminiferous ether by making it clear that it didn’t exist. Einstein gave us a universe that didn’t need it.

Physicists as a rule are not overattentive to the pronouncements of Swiss patent office clerks, and so, despite the abundance of useful tidings, Einstein’s papers attracted little notice. Having just solved several of the deepest mysteries of the universe, Einstein applied for a job as a university lecturer and was rejected, and then as a high school teacher and was rejected there as well. So he went back to his job as an examiner third class, but of course he kept thinking. He hadn’t even come close to finishing yet.

When the poet Paul Valéry once asked Einstein if he kept a notebook to record his ideas, Einstein looked at him with mild but genuine surprise. “Oh, that’s not necessary,” he replied. “It’s so seldom I have one.” I need hardly point out that when he did get one it tended to be good. Einstein’s next idea was one of the greatest that anyone has ever had-indeed, the very greatest, according to Boorse, Motz, and Weaver in their thoughtful history of atomic science. “As the creation of a single mind,” they write, “it is undoubtedly the highest intellectual achievement of humanity,” which is of course as good as a compliment can get.

In 1907, or so it has sometimes been written, Albert Einstein saw a workman fall off a roof and began to think about gravity. Alas, like many good stories this one appears to be apocryphal. According to Einstein himself, he was simply sitting in a chair when the problem of gravity occurred to him.

Actually, what occurred to Einstein was something more like the beginning of a solution to the problem of gravity, since it had been evident to him from the outset that one thing missing from the special theory was gravity. What was “special” about the special theory was that it dealt with things moving in an essentially unimpeded state. But what happened when a thing in motion-light, above all-encountered an obstacle such as gravity? It was a question that would occupy his thoughts for most of the next decade and lead to the publication in early 1917 of a paper entitled “Cosmological Considerations on the General Theory of Relativity.” The special theory of relativity of 1905 was a profound and important piece of work, of course, but as C. P. Snow once observed, if Einstein hadn’t thought of it when he did someone else would have, probably within five years; it was an idea waiting to happen. But the general theory was something else altogether. “Without it,” wrote Snow in 1979, “it is likely that we should still be waiting for the theory today.”

With his pipe, genially self-effacing manner, and electrified hair, Einstein was too splendid a figure to remain permanently obscure, and in 1919, the war over, the world suddenly discovered him. Almost at once his theories of relativity developed a reputation for being impossible for an ordinary person to grasp. Matters were not helped, as David Bodanis points out in his superb book E=mc², when the New York Times decided to do a story, and-for reasons that can never fail to excite wonder-sent the paper’s golfing correspondent, one Henry Crouch, to conduct the interview.

Crouch was hopelessly out of his depth, and got nearly everything wrong. Among the more lasting errors in his report was the assertion that Einstein had found a publisher daring enough to publish a book that only twelve men “in all the world could comprehend.” There was no such book, no such publisher, no such circle of learned men, but the notion stuck anyway. Soon the number of people who could grasp relativity had been reduced even further in the popular imagination-and the scientific establishment, it must be said, did little to disturb the myth.

When a journalist asked the British astronomer Sir Arthur Eddington if it was true that he was one of only three people in the world who could understand Einstein’s relativity theories, Eddington considered deeply for a moment and replied: “I am trying to think who the third person is.” In fact, the problem with relativity wasn’t that it involved a lot of differential equations, Lorentz transformations, and other complicated mathematics (though it did-even Einstein needed help with some of it), but that it was just so thoroughly nonintuitive.

In essence what relativity says is that space and time are not absolute, but relative to both the observer and to the thing being observed, and the faster one moves the more pronounced these effects become. We can never accelerate ourselves to the speed of light, and the harder we try (and faster we go) the more distorted we will become, relative to an outside observer.

Almost at once popularizers of science tried to come up with ways to make these concepts accessible to a general audience. One of the more successful attempts-commercially at least-was The ABC of Relativity by the mathematician and philosopher Bertrand Russell. In it, Russell employed an image that has been used many times since. He asked the reader to envision a train one hundred yards long moving at 60 percent of the speed of light. To someone standing on a platform watching it pass, the train would appear to be only eighty yards long and everything on it would be similarly compressed. If we could hear the passengers on the train speak, their voices would sound slurred and sluggish, like a record played at too slow a speed, and their movements would appear similarly ponderous. Even the clocks on the train would seem to be running at only four-fifths of their normal speed.

However-and here’s the thing-people on the train would have no sense of these distortions. To them, everything on the train would seem quite normal. It would be we on the platform who looked weirdly compressed and slowed down. It is all to do, you see, with your position relative to the moving object.

This effect actually happens every time you move. Fly across the United States, and you will step from the plane a quinzillionth of a second, or something, younger than those you left behind. Even in walking across the room you will very slightly alter your own experience of time and space. It has been calculated that a baseball thrown at a hundred miles an hour will pick up 0.000000000002 grams of mass on its way to home plate. So the effects of relativity are real and have been measured. The problem is that such changes are much too small to make the tiniest detectable difference to us. But for other things in the universe-light, gravity, the universe itself-these are matters of consequence.

So if the ideas of relativity seem weird, it is only because we don’t experience these sorts of interactions in normal life. However, to turn to Bodanis again, we all commonly encounter other kinds of relativity-for instance with regard to sound. If you are in a park and someone is playing annoying music, you know that if you move to a more distant spot the music will seem quieter. That’s not because the music is quieter, of course, but simply that your position relative to it has changed. To something too small or sluggish to duplicate this experience-a snail, say-the idea that a boom box could seem to two observers to produce two different volumes of music simultaneously might seem incredible.

The most challenging and nonintuitive of all the concepts in the general theory of relativity is the idea that time is part of space. Our instinct is to regard time as eternal, absolute, immutable-nothing can disturb its steady tick. In fact, according to Einstein, time is variable and ever changing. It even has shape. It is bound up-“inextricably interconnected,” in Stephen Hawking’s expression-with the three dimensions of space in a curious dimension known as spacetime.

Spacetime is usually explained by asking you to imagine something flat but pliant-a mattress, say, or a sheet of stretched rubber-on which is resting a heavy round object, such as an iron ball. The weight of the iron ball causes the material on which it is sitting to stretch and sag slightly. This is roughly analogous to the effect that a massive object such as the Sun (the iron ball) has on spacetime (the material): it stretches and curves and warps it. Now if you roll a smaller ball across the sheet, it tries to go in a straight line as required by Newton’s laws of motion, but as it nears the massive object and the slope of the sagging fabric, it rolls downward, ineluctably drawn to the more massive object. This is gravity-a product of the bending of spacetime.

Every object that has mass creates a little depression in the fabric of the cosmos. Thus the universe, as Dennis Overbye has put it, is “the ultimate sagging mattress.” Gravity on this view is no longer so much a thing as an outcome-“not a ‘force’ but a byproduct of the warping of spacetime,” in the words of the physicist Michio Kaku, who goes on: “In some sense, gravity does not exist; what moves the planets and stars is the distortion of space and time.”

Of course the sagging mattress analogy can take us only so far because it doesn’t incorporate the effect of time. But then our brains can take us only so far because it is so nearly impossible to envision a dimension comprising three parts space to one part time, all interwoven like the threads in a plaid fabric. At all events, I think we can agree that this was an awfully big thought for a young man staring out the window of a patent office in the capital of Switzerland.

Among much else, Einstein’s general theory of relativity suggested that the universe must be either expanding or contracting. But Einstein was not a cosmologist, and he accepted the prevailing wisdom that the universe was fixed and eternal. More or less reflexively, he dropped into his equations something called the cosmological constant, which arbitrarily counterbalanced the effects of gravity, serving as a kind of mathematical pause button. Books on the history of science always forgive Einstein this lapse, but it was actually a fairly appalling piece of science and he knew it. He called it “the biggest blunder of my life.”

Coincidentally, at about the time that Einstein was affixing a cosmological constant to his theory, at the Lowell Observatory in Arizona, an astronomer with the cheerily intergalactic name of Vesto Slipher (who was in fact from Indiana) was taking spectrographic readings of distant stars and discovering that they appeared to be moving away from us. The universe wasn’t static. The stars Slipher looked at showed unmistakable signs of a Doppler shift[20]-the same mechanism behind that distinctive stretched-out yee-yummm sound cars make as they flash past on a racetrack. The phenomenon also applies to light, and in the case of receding galaxies it is known as a red shift (because light moving away from us shifts toward the red end of the spectrum; approaching light shifts to blue).

Slipher was the first to notice this effect with light and to realize its potential importance for understanding the motions of the cosmos. Unfortunately no one much noticed him. The Lowell Observatory, as you will recall, was a bit of an oddity thanks to Percival Lowell’s obsession with Martian canals, which in the 1910s made it, in every sense, an outpost of astronomical endeavor. Slipher was unaware of Einstein’s theory of relativity, and the world was equally unaware of Slipher. So his finding had no impact.

Glory instead would pass to a large mass of ego named Edwin Hubble. Hubble was born in 1889, ten years after Einstein, in a small Missouri town on the edge of the Ozarks and grew up there and in Wheaton, Illinois, a suburb of Chicago. His father was a successful insurance executive, so life was always comfortable, and Edwin enjoyed a wealth of physical endowments, too. He was a strong and gifted athlete, charming, smart, and immensely good-looking-“handsome almost to a fault,” in the description of William H. Cropper, “an Adonis” in the words of another admirer. According to his own accounts, he also managed to fit into his life more or less constant acts of valor-rescuing drowning swimmers, leading frightened men to safety across the battlefields of France, embarrassing world-champion boxers with knockdown punches in exhibition bouts. It all seemed too good to be true. It was. For all his gifts, Hubble was also an inveterate liar.

This was more than a little odd, for Hubble’s life was filled from an early age with a level of distinction that was at times almost ludicrously golden. At a single high school track meet in 1906, he won the pole vault, shot put, discus, hammer throw, standing high jump, and running high jump, and was on the winning mile-relay team-that is seven first places in one meet-and came in third in the broad jump. In the same year, he set a state record for the high jump in Illinois.

As a scholar he was equally proficient, and had no trouble gaining admission to study physics and astronomy at the University of Chicago (where, coincidentally, the head of the department was now Albert Michelson). There he was selected to be one of the first Rhodes scholars at Oxford. Three years of English life evidently turned his head, for he returned to Wheaton in 1913 wearing an Inverness cape, smoking a pipe, and talking with a peculiarly orotund accent-not quite British but not quite not-that would remain with him for life. Though he later claimed to have passed most of the second decade of the century practicing law in Kentucky, in fact he worked as a high school teacher and basketball coach in New Albany, Indiana, before belatedly attaining his doctorate and passing briefly through the Army. (He arrived in France one month before the Armistice and almost certainly never heard a shot fired in anger.)

In 1919, now aged thirty, he moved to California and took up a position at the Mount Wilson Observatory near Los Angeles. Swiftly, and more than a little unexpectedly, he became the most outstanding astronomer of the twentieth century.

It is worth pausing for a moment to consider just how little was known of the cosmos at this time. Astronomers today believe there are perhaps 140 billion galaxies in the visible universe. That’s a huge number, much bigger than merely saying it would lead you to suppose. If galaxies were frozen peas, it would be enough to fill a large auditorium-the old Boston Garden, say, or the Royal Albert Hall. (An astrophysicist named Bruce Gregory has actually computed this.) In 1919, when Hubble first put his head to the eyepiece, the number of these galaxies that were known to us was exactly one: the Milky Way. Everything else was thought to be either part of the Milky Way itself or one of many distant, peripheral puffs of gas. Hubble quickly demonstrated how wrong that belief was.

Over the next decade, Hubble tackled two of the most fundamental questions of the universe: how old is it, and how big? To answer both it is necessary to know two things-how far away certain galaxies are and how fast they are flying away from us (what is known as their recessional velocity). The red shift gives the speed at which galaxies are retiring, but doesn’t tell us how far away they are to begin with. For that you need what are known as “standard candles”-stars whose brightness can be reliably calculated and used as benchmarks to measure the brightness (and hence relative distance) of other stars.

Hubble’s luck was to come along soon after an ingenious woman named Henrietta Swan Leavitt had figured out a way to do so. Leavitt worked at the Harvard College Observatory as a computer, as they were known. Computers spent their lives studying photographic plates of stars and making computations-hence the name. It was little more than drudgery by another name, but it was as close as women could get to real astronomy at Harvard-or indeed pretty much anywhere-in those days. The system, however unfair, did have certain unexpected benefits: it meant that half the finest minds available were directed to work that would otherwise have attracted little reflective attention, and it ensured that women ended up with an appreciation of the fine structure of the cosmos that often eluded their male counterparts.

One Harvard computer, Annie Jump Cannon, used her repetitive acquaintance with the stars to devise a system of stellar classifications so practical that it is still in use today. Leavitt’s contribution was even more profound. She noticed that a type of star known as a Cepheid variable (after the constellation Cepheus, where it first was identified) pulsated with a regular rhythm-a kind of stellar heartbeat. Cepheids are quite rare, but at least one of them is well known to most of us. Polaris, the Pole Star, is a Cepheid.

We now know that Cepheids throb as they do because they are elderly stars that have moved past their “main sequence phase,” in the parlance of astronomers, and become red giants. The chemistry of red giants is a little weighty for our purposes here (it requires an appreciation for the properties of singly ionized helium atoms, among quite a lot else), but put simply it means that they burn their remaining fuel in a way that produces a very rhythmic, very reliable brightening and dimming. Leavitt’s genius was to realize that by comparing the relative magnitudes of Cepheids at different points in the sky you could work out where they were in relation to each other. They could be used as “standard candles”-a term she coined and still in universal use. The method provided only relative distances, not absolute distances, but even so it was the first time that anyone had come up with a usable way to measure the large-scale universe.

(Just to put these insights into perspective, it is perhaps worth noting that at the time Leavitt and Cannon were inferring fundamental properties of the cosmos from dim smudges on photographic plates, the Harvard astronomer William H. Pickering, who could of course peer into a first-class telescope as often as he wanted, was developing his seminal theory that dark patches on the Moon were caused by swarms of seasonally migrating insects.)

Combining Leavitt’s cosmic yardstick with Vesto Slipher’s handy red shifts, Edwin Hubble now began to measure selected points in space with a fresh eye. In 1923 he showed that a puff of distant gossamer in the Andromeda constellation known as M31 wasn’t a gas cloud at all but a blaze of stars, a galaxy in its own right, a hundred thousand light-years across and at least nine hundred thousand light-years away. The universe was vaster-vastly vaster-than anyone had ever supposed. In 1924 he produced a landmark paper, “Cepheids in Spiral Nebulae” (nebulae, from the Latin for “clouds,” was his word for galaxies), showing that the universe consisted not just of the Milky Way but of lots of independent galaxies-“island universes”-many of them bigger than the Milky Way and much more distant.

This finding alone would have ensured Hubble’s reputation, but he now turned to the question of working out just how much vaster the universe was, and made an even more striking discovery. Hubble began to measure the spectra of distant galaxies-the business that Slipher had begun in Arizona. Using Mount Wilson’s new hundred-inch Hooker telescope and some clever inferences, he worked out that all the galaxies in the sky (except for our own local cluster) are moving away from us. Moreover, their speed and distance were neatly proportional: the further away the galaxy, the faster it was moving.

This was truly startling. The universe was expanding, swiftly and evenly in all directions. It didn’t take a huge amount of imagination to read backwards from this and realize that it must therefore have started from some central point. Far from being the stable, fixed, eternal void that everyone had always assumed, this was a universe that had a beginning. It might therefore also have an end.

The wonder, as Stephen Hawking has noted, is that no one had hit on the idea of the expanding universe before. A static universe, as should have been obvious to Newton and every thinking astronomer since, would collapse in upon itself. There was also the problem that if stars had been burning indefinitely in a static universe they’d have made the whole intolerably hot-certainly much too hot for the likes of us. An expanding universe resolved much of this at a stroke.

Hubble was a much better observer than a thinker and didn’t immediately appreciate the full implications of what he had found. Partly this was because he was woefully ignorant of Einstein’s General Theory of Relativity. This was quite remarkable because, for one thing, Einstein and his theory were world famous by now. Moreover, in 1929 Albert Michelson-now in his twilight years but still one of the world’s most alert and esteemed scientists-accepted a position at Mount Wilson to measure the velocity of light with his trusty interferometer, and must surely have at least mentioned to him the applicability of Einstein’s theory to his own findings.

At all events, Hubble failed to make theoretical hay when the chance was there. Instead, it was left to a Belgian priest-scholar (with a Ph.D. from MIT) named Georges Lemaître to bring together the two strands in his own “fireworks theory,” which suggested that the universe began as a geometrical point, a “primeval atom,” which burst into glory and had been moving apart ever since. It was an idea that very neatly anticipated the modern conception of the Big Bang but was so far ahead of its time that Lemaître seldom gets more than the sentence or two that we have given him here. The world would need additional decades, and the inadvertent discovery of cosmic background radiation by Penzias and Wilson at their hissing antenna in New Jersey, before the Big Bang would begin to move from interesting idea to established theory.

Neither Hubble nor Einstein would be much of a part of that big story. Though no one would have guessed it at the time, both men had done about as much as they were ever going to do.

In 1936 Hubble produced a popular book called The Realm of the Nebulae, which explained in flattering style his own considerable achievements. Here at last he showed that he had acquainted himself with Einstein’s theory-up to a point anyway: he gave it four pages out of about two hundred.

Hubble died of a heart attack in 1953. One last small oddity awaited him. For reasons cloaked in mystery, his wife declined to have a funeral and never revealed what she did with his body. Half a century later the whereabouts of the century’s greatest astronomer remain unknown. For a memorial you must look to the sky and the Hubble Space Telescope, launched in 1990 and named in his honor.

9 THE MIGHTY ATOM

WHILE EINSTEIN AND Hubble were productively unraveling the large-scale structure of the cosmos, others were struggling to understand something closer to hand but in its way just as remote: the tiny and ever- mysterious atom.

The great Caltech physicist Richard Feynman once observed that if you had to reduce scientific history to one important statement it would be “All things are made of atoms.” They are everywhere and they constitute every thing. Look around you. It is all atoms. Not just the solid things like walls and tables and sofas, but the air in between. And they are there in numbers that you really cannot conceive.

The basic working arrangement of atoms is the molecule (from the Latin for “little mass”). A molecule is simply two or more atoms working together in a more or less stable arrangement: add two atoms of hydrogen to one of oxygen and you have a molecule of water. Chemists tend to think in terms of molecules rather than elements in much the way that writers tend to think in terms of words and not letters, so it is molecules they count, and these are numerous to say the least. At sea level, at a temperature of 32 degrees Fahrenheit, one cubic centimeter of air (that is, a space about the size of a sugar cube) will contain 45 billion billion molecules. And they are in every single cubic centimeter you see around you. Think how many cubic centimeters there are in the world outside your window-how many sugar cubes it would take to fill that view. Then think how many it would take to build a universe. Atoms, in short, are very abundant.

They are also fantastically durable. Because they are so long lived, atoms really get around. Every atom you possess has almost certainly passed through several stars and been part of millions of organisms on its way to becoming you. We are each so atomically numerous and so vigorously recycled at death that a significant number of our atoms-up to a billion for each of us, it has been suggested-probably once belonged to Shakespeare. A billion more each came from Buddha and Genghis Khan and Beethoven, and any other historical figure you care to name. (The personages have to be historical, apparently, as it takes the atoms some decades to become thoroughly redistributed; however much you may wish it, you are not yet one with Elvis Presley.)

So we are all reincarnations-though short-lived ones. When we die our atoms will disassemble and move off to find new uses elsewhere-as part of a leaf or other human being or drop of dew. Atoms, however, go on practically forever. Nobody actually knows how long an atom can survive, but according to Martin Rees it is probably about 10³⁵ years-a number so big that even I am happy to express it in notation.

Above all, atoms are tiny-very tiny indeed. Half a million of them lined up shoulder to shoulder could hide behind a human hair. On such a scale an individual atom is essentially impossible to imagine, but we can of course try.

Start with a millimeter, which is a line this long: -. Now imagine that line divided into a thousand equal widths. Each of those widths is a micron. This is the scale of microorganisms. A typical paramecium, for instance, is about two microns wide, 0.002 millimeters, which is really very small. If you wanted to see with your naked eye a paramecium swimming in a drop of water, you would have to enlarge the drop until it was some forty feet across. However, if you wanted to see the atoms in the same drop, you would have to make the drop fifteen miles across.

Atoms, in other words, exist on a scale of minuteness of another order altogether. To get down to the scale of atoms, you would need to take each one of those micron slices and shave it into ten thousand finer widths. That’s the scale of an atom: one ten-millionth of a millimeter. It is a degree of slenderness way beyond the capacity of our imaginations, but you can get some idea of the proportions if you bear in mind that one atom is to the width of a millimeter line as the thickness of a sheet of paper is to the height of the Empire State Building.

It is of course the abundance and extreme durability of atoms that makes them so useful, and the tininess that makes them so hard to detect and understand. The realization that atoms are these three things-small, numerous, practically indestructible-and that all things are made from them first occurred not to Antoine-Laurent Lavoisier, as you might expect, or even to Henry Cavendish or Humphry Davy, but rather to a spare and lightly educated English Quaker named John Dalton, whom we first encountered in the chapter on chemistry.

Dalton was born in 1766 on the edge of the Lake District near Cockermouth to a family of poor but devout Quaker weavers. (Four years later the poet William Wordsworth would also join the world at Cockermouth.) He was an exceptionally bright student-so very bright indeed that at the improbably youthful age of twelve he was put in charge of the local Quaker school. This perhaps says as much about the school as about Dalton’s precocity, but perhaps not: we know from his diaries that at about this time he was reading Newton’s Principia in the original Latin and other works of a similarly challenging nature. At fifteen, still schoolmastering, he took a job in the nearby town of Kendal, and a decade after that he moved to Manchester, scarcely stirring from there for the remaining fifty years of his life. In Manchester he became something of an intellectual whirlwind, producing books and papers on subjects ranging from meteorology to grammar. Color blindness, a condition from which he suffered, was for a long time called Daltonism because of his studies. But it was a plump book called A New System of Chemical Philosophy, published in 1808, that established his reputation.

There, in a short chapter of just five pages (out of the book’s more than nine hundred), people of learning first encountered atoms in something approaching their modern conception. Dalton’s simple insight was that at the root of all matter are exceedingly tiny, irreducible particles. “We might as well attempt to introduce a new planet into the solar system or annihilate one already in existence, as to create or destroy a particle of hydrogen,” he wrote.

Neither the idea of atoms nor the term itself was exactly new. Both had been developed by the ancient Greeks. Dalton’s contribution was to consider the relative sizes and characters of these atoms and how they fit together. He knew, for instance, that hydrogen was the lightest element, so he gave it an atomic weight of one. He believed also that water consisted of seven parts of oxygen to one of hydrogen, and so he gave oxygen an atomic weight of seven. By such means was he able to arrive at the relative weights of the known elements. He wasn’t always terribly accurate-oxygen’s atomic weight is actually sixteen, not seven-but the principle was sound and formed the basis for all of modern chemistry and much of the rest of modern science.

The work made Dalton famous-albeit in a low-key, English Quaker sort of way. In 1826, the French chemist P .J. Pelletier traveled to Manchester to meet the atomic hero. Pelletier expected to find him attached to some grand institution, so he was astounded to discover him teaching elementary arithmetic to boys in a small school on a back street. According to the scientific historian E. J. Holmyard, a confused Pelletier, upon beholding the great man, stammered:

“Est-ce que j’ai l’honneur de m’addresser à Monsieur Dalton?” for he could hardly believe his eyes that this was the chemist of European fame, teaching a boy his first four rules. “Yes,” said the matter-of-fact Quaker. “Wilt thou sit down whilst I put this lad right about his arithmetic?”

Although Dalton tried to avoid all honors, he was elected to the Royal Society against his wishes, showered with medals, and given a handsome government pension. When he died in 1844, forty thousand people viewed the coffin, and the funeral cortege stretched for two miles. His entry in the Dictionary of National Biography is one of the longest, rivaled in length only by those of Darwin and Lyell among nineteenth-century men of science.

For a century after Dalton made his proposal, it remained entirely hypothetical, and a few eminent scientists-notably the Viennese physicist Ernst Mach, for whom is named the speed of sound-doubted the existence of atoms at all. “Atoms cannot be perceived by the senses . . . they are things of thought,” he wrote. The existence of atoms was so doubtfully held in the German-speaking world in particular that it was said to have played a part in the suicide of the great theoretical physicist, and atomic enthusiast, Ludwig Boltzmann in 1906.

It was Einstein who provided the first incontrovertible evidence of atoms’ existence with his paper on Brownian motion in 1905, but this attracted little attention and in any case Einstein was soon to become consumed with his work on general relativity. So the first real hero of the atomic age, if not the first personage on the scene, was Ernest Rutherford.

Rutherford was born in 1871 in the “back blocks” of New Zealand to parents who had emigrated from Scotland to raise a little flax and a lot of children (to paraphrase Steven Weinberg). Growing up in a remote part of a remote country, he was about as far from the mainstream of science as it was possible to be, but in 1895 he won a scholarship that took him to the Cavendish Laboratory at Cambridge University, which was about to become the hottest place in the world to do physics.

Physicists are notoriously scornful of scientists from other fields. When the wife of the great Austrian physicist Wolfgang Pauli left him for a chemist, he was staggered with disbelief. “Had she taken a bullfighter I would have understood,” he remarked in wonder to a friend. “But a chemist . . .”

It was a feeling Rutherford would have understood. “All science is either physics or stamp collecting,” he once said, in a line that has been used many times since. There is a certain engaging irony therefore that when he won the Nobel Prize in 1908, it was in chemistry, not physics.

Rutherford was a lucky man-lucky to be a genius, but even luckier to live at a time when physics and chemistry were so exciting and so compatible (his own sentiments notwithstanding). Never again would they quite so comfortably overlap.

For all his success, Rutherford was not an especially brilliant man and was actually pretty terrible at mathematics. Often during lectures he would get so lost in his own equations that he would give up halfway through and tell the students to work it out for themselves. According to his longtime colleague James Chadwick, discoverer of the neutron, he wasn’t even particularly clever at experimentation. He was simply tenacious and open-minded. For brilliance he substituted shrewdness and a kind of daring. His mind, in the words of one biographer, was “always operating out towards the frontiers, as far as he could see, and that was a great deal further than most other men.” Confronted with an intractable problem, he was prepared to work at it harder and longer than most people and to be more receptive to unorthodox explanations. His greatest breakthrough came because he was prepared to spend immensely tedious hours sitting at a screen counting alpha particle scintillations, as they were known-the sort of work that would normally have been farmed out. He was one of the first to see-possibly the very first-that the power inherent in the atom could, if harnessed, make bombs powerful enough to “make this old world vanish in smoke.”

Physically he was big and booming, with a voice that made the timid shrink. Once when told that Rutherford was about to make a radio broadcast across the Atlantic, a colleague drily asked: “Why use radio?” He also had a huge amount of good-natured confidence. When someone remarked to him that he seemed always to be at the crest of a wave, he responded, “Well, after all, I made the wave, didn’t I?” C. P. Snow recalled how once in a Cambridge tailor’s he overheard Rutherford remark: “Every day I grow in girth. And in mentality.”

But both girth and fame were far ahead of him in 1895 when he fetched up at the Cavendish.[20] It was a singularly eventful period in science. In the year of his arrival in Cambridge, Wilhelm Roentgen discovered X rays at the University of Würzburg in Germany, and the next year Henri Becquerel discovered radioactivity. And the Cavendish itself was about to embark on a long period of greatness. In 1897, J. J. Thomson and colleagues would discover the electron there, in 1911 C. T. R. Wilson would produce the first particle detector there (as we shall see), and in 1932 James Chadwick would discover the neutron there. Further still in the future, James Watson and Francis Crick would discover the structure of DNA at the Cavendish in 1953.

In the beginning Rutherford worked on radio waves, and with some distinction-he managed to transmit a crisp signal more than a mile, a very reasonable achievement for the time-but gave it up when he was persuaded by a senior colleague that radio had little future. On the whole, however, Rutherford didn’t thrive at the Cavendish. After three years there, feeling he was going nowhere, he took a post at McGill University in Montreal, and there he began his long and steady rise to greatness. By the time he received his Nobel Prize (for “investigations into the disintegration of the elements, and the chemistry of radioactive substances,” according to the official citation) he had moved on to Manchester University, and it was there, in fact, that he would do his most important work in determining the structure and nature of the atom.

By the early twentieth century it was known that atoms were made of parts-Thomson’s discovery of the electron had established that-but it wasn’t known how many parts there were or how they fit together or what shape they took. Some physicists thought that atoms might be cube shaped, because cubes can be packed together so neatly without any wasted space. The more general view, however, was that an atom was more like a currant bun or a plum pudding: a dense, solid object that carried a positive charge but that was studded with negatively charged electrons, like the currants in a currant bun.

In 1910, Rutherford (assisted by his student Hans Geiger, who would later invent the radiation detector that bears his name) fired ionized helium atoms, or alpha particles, at a sheet of gold foil.[21] To Rutherford’s astonishment, some of the particles bounced back. It was as if, he said, he had fired a fifteen-inch shell at a sheet of paper and it rebounded into his lap. This was just not supposed to happen. After considerable reflection he realized there could be only one possible explanation: the particles that bounced back were striking something small and dense at the heart of the atom, while the other particles sailed through unimpeded. An atom, Rutherford realized, was mostly empty space, with a very dense nucleus at the center. This was a most gratifying discovery, but it presented one immediate problem. By all the laws of conventional physics, atoms shouldn’t therefore exist.

Let us pause for a moment and consider the structure of the atom as we know it now. Every atom is made from three kinds of elementary particles: protons, which have a positive electrical charge; electrons, which have a negative electrical charge; and neutrons, which have no charge. Protons and neutrons are packed into the nucleus, while electrons spin around outside. The number of protons is what gives an atom its chemical identity. An atom with one proton is an atom of hydrogen, one with two protons is helium, with three protons is lithium, and so on up the scale. Each time you add a proton you get a new element. (Because the number of protons in an atom is always balanced by an equal number of electrons, you will sometimes see it written that it is the number of electrons that defines an element; it comes to the same thing. The way it was explained to me is that protons give an atom its identity, electrons its personality.)

Neutrons don’t influence an atom’s identity, but they do add to its mass. The number of neutrons is generally about the same as the number of protons, but they can vary up and down slightly. Add a neutron or two and you get an isotope. The terms you hear in reference to dating techniques in archeology refer to isotopes-carbon-14, for instance, which is an atom of carbon with six protons and eight neutrons (the fourteen being the sum of the two).

Neutrons and protons occupy the atom’s nucleus. The nucleus of an atom is tiny-only one millionth of a billionth of the full volume of the atom-but fantastically dense, since it contains virtually all the atom’s mass. As Cropper has put it, if an atom were expanded to the size of a cathedral, the nucleus would be only about the size of a fly-but a fly many thousands of times heavier than the cathedral. It was this spaciousness-this resounding, unexpected roominess-that had Rutherford scratching his head in 1910.

It is still a fairly astounding notion to consider that atoms are mostly empty space, and that the solidity we experience all around us is an illusion. When two objects come together in the real world-billiard balls are most often used for illustration-they don’t actually strike each other. “Rather,” as Timothy Ferris explains, “the negatively charged fields of the two balls repel each other . . . were it not for their electrical charges they could, like galaxies, pass right through each other unscathed.” When you sit in a chair, you are not actually sitting there, but levitating above it at a height of one angstrom (a hundred millionth of a centimeter), your electrons and its electrons implacably opposed to any closer intimacy.

The picture that nearly everybody has in mind of an atom is of an electron or two flying around a nucleus, like planets orbiting a sun. This image was created in 1904, based on little more than clever guesswork, by a Japanese physicist named Hantaro Nagaoka. It is completely wrong, but durable just the same. As Isaac Asimov liked to note, it inspired generations of science fiction writers to create stories of worlds within worlds, in which atoms become tiny inhabited solar systems or our solar system turns out to be merely a mote in some much larger scheme. Even now CERN, the European Organization for Nuclear Research, uses Nagaoka’s image as a logo on its website. In fact, as physicists were soon to realize, electrons are not like orbiting planets at all, but more like the blades of a spinning fan, managing to fill every bit of space in their orbits simultaneously (but with the crucial difference that the blades of a fan only seem to be everywhere at once; electrons are).

Needless to say, very little of this was understood in 1910 or for many years afterward. Rutherford’s finding presented some large and immediate problems, not least that no electron should be able to orbit a nucleus without crashing. Conventional electrodynamic theory demanded that a flying electron should very quickly run out of energy-in only an instant or so-and spiral into the nucleus, with disastrous consequences for both. There was also the problem of how protons with their positive charges could bundle together inside the nucleus without blowing themselves and the rest of the atom apart. Clearly whatever was going on down there in the world of the very small was not governed by the laws that applied in the macro world where our expectations reside.

As physicists began to delve into this subatomic realm, they realized that it wasn’t merely different from anything we knew, but different from anything ever imagined. “Because atomic behavior is so unlike ordinary experience,” Richard Feynman once observed, “it is very difficult to get used to and it appears peculiar and mysterious to everyone, both to the novice and to the experienced physicist.” When Feynman made that comment, physicists had had half a century to adjust to the strangeness of atomic behavior. So think how it must have felt to Rutherford and his colleagues in the early 1910s when it was all brand new.

One of the people working with Rutherford was a mild and affable young Dane named Niels Bohr. In 1913, while puzzling over the structure of the atom, Bohr had an idea so exciting that he postponed his honeymoon to write what became a landmark paper. Because physicists couldn’t see anything so small as an atom, they had to try to work out its structure from how it behaved when they did things to it, as Rutherford had done by firing alpha particles at foil. Sometimes, not surprisingly, the results of these experiments were puzzling. One puzzle that had been around for a long time had to do with spectrum readings of the wavelengths of hydrogen. These produced patterns showing that hydrogen atoms emitted energy at certain wavelengths but not others. It was rather as if someone under surveillance kept turning up at particular locations but was never observed traveling between them. No one could understand why this should be.

It was while puzzling over this problem that Bohr was struck by a solution and dashed off his famous paper. Called “On the Constitutions of Atoms and Molecules,” the paper explained how electrons could keep from falling into the nucleus by suggesting that they could occupy only certain well-defined orbits. According to the new theory, an electron moving between orbits would disappear from one and reappear instantaneously in another without visiting the space between. This idea-the famous “quantum leap”-is of course utterly strange, but it was too good not to be true. It not only kept electrons from spiraling catastrophically into the nucleus; it also explained hydrogen’s bewildering wavelengths. The electrons only appeared in certain orbits because they only existed in certain orbits. It was a dazzling insight, and it won Bohr the 1922 Nobel Prize in physics, the year after Einstein received his.

Meanwhile the tireless Rutherford, now back at Cambridge as J. J. Thomson’s successor as head of the Cavendish Laboratory, came up with a model that explained why the nuclei didn’t blow up. He saw that they must be offset by some type of neutralizing particles, which he called neutrons. The idea was simple and appealing, but not easy to prove. Rutherford’s associate, James Chadwick, devoted eleven intensive years to hunting for neutrons before finally succeeding in 1932. He, too, was awarded with a Nobel Prize in physics, in 1935. As Boorse and his colleagues point out in their history of the subject, the delay in discovery was probably a very good thing as mastery of the neutron was essential to the development of the atomic bomb. (Because neutrons have no charge, they aren’t repelled by the electrical fields at the heart of an atom and thus could be fired like tiny torpedoes into an atomic nucleus, setting off the destructive process known as fission.) Had the neutron been isolated in the 1920s, they note, it is “very likely the atomic bomb would have been developed first in Europe, undoubtedly by the Germans.”

As it was, the Europeans had their hands full trying to understand the strange behavior of the electron. The principal problem they faced was that the electron sometimes behaved like a particle and sometimes like a wave. This impossible duality drove physicists nearly mad. For the next decade all across Europe they furiously thought and scribbled and offered competing hypotheses. In France, Prince Louis-Victor de Broglie, the scion of a ducal family, found that certain anomalies in the behavior of electrons disappeared when one regarded them as waves. The observation excited the attention of the Austrian Erwin Schrödinger, who made some deft refinements and devised a handy system called wave mechanics. At almost the same time the German physicist Werner Heisenberg came up with a competing theory called matrix mechanics. This was so mathematically complex that hardly anyone really understood it, including Heisenberg himself (“I do not even know what a matrix is,” Heisenberg despaired to a friend at one point), but it did seem to solve certain problems that Schrödinger’s waves failed to explain.

The upshot is that physics had two theories, based on conflicting premises, that produced the same results. It was an impossible situation.

Finally, in 1926, Heisenberg came up with a celebrated compromise, producing a new discipline that came to be known as quantum mechanics. At the heart of it was Heisenberg’s Uncertainty Principle, which states that the electron is a particle but a particle that can be described in terms of waves. The uncertainty around which the theory is built is that we can know the path an electron takes as it moves through a space or we can know where it is at a given instant, but we cannot know both.[22] Any attempt to measure one will unavoidably disturb the other. This isn’t a matter of simply needing more precise instruments; it is an immutable property of the universe.

What this means in practice is that you can never predict where an electron will be at any given moment. You can only list its probability of being there. In a sense, as Dennis Overbye has put it, an electron doesn’t exist until it is observed. Or, put slightly differently, until it is observed an electron must be regarded as being “at once everywhere and nowhere.”

If this seems confusing, you may take some comfort in knowing that it was confusing to physicists, too. Overbye notes: “Bohr once commented that a person who wasn’t outraged on first hearing about quantum theory didn’t understand what had been said.” Heisenberg, when asked how one could envision an atom, replied: “Don’t try.”

So the atom turned out to be quite unlike the image that most people had created. The electron doesn’t fly around the nucleus like a planet around its sun, but instead takes on the more amorphous aspect of a cloud. The “shell” of an atom isn’t some hard shiny casing, as illustrations sometimes encourage us to suppose, but simply the outermost of these fuzzy electron clouds. The cloud itself is essentially just a zone of statistical probability marking the area beyond which the electron only very seldom strays. Thus an atom, if you could see it, would look more like a very fuzzy tennis ball than a hard-edged metallic sphere (but not much like either or, indeed, like anything you’ve ever seen; we are, after all, dealing here with a world very different from the one we see around us).

It seemed as if there was no end of strangeness. For the first time, as James Trefil has put it, scientists had encountered “an area of the universe that our brains just aren’t wired to understand.” Or as Feynman expressed it, “things on a small scale behave nothing like things on a large scale.” As physicists delved deeper, they realized they had found a world where not only could electrons jump from one orbit to another without traveling across any intervening space, but matter could pop into existence from nothing at all-“provided,” in the words of Alan Lightman of MIT, “it disappears again with sufficient haste.”

Perhaps the most arresting of quantum improbabilities is the idea, arising from Wolfgang Pauli’s Exclusion Principle of 1925, that the subatomic particles in certain pairs, even when separated by the most considerable distances, can each instantly “know” what the other is doing. Particles have a quality known as spin and, according to quantum theory, the moment you determine the spin of one particle, its sister particle, no matter how distant away, will immediately begin spinning in the opposite direction and at the same rate.

It is as if, in the words of the science writer Lawrence Joseph, you had two identical pool balls, one in Ohio and the other in Fiji, and the instant you sent one spinning the other would immediately spin in a contrary direction at precisely the same speed. Remarkably, the phenomenon was proved in 1997 when physicists at the University of Geneva sent photons seven miles in opposite directions and demonstrated that interfering with one provoked an instantaneous response in the other.

Things reached such a pitch that at one conference Bohr remarked of a new theory that the question was not whether it was crazy, but whether it was crazy enough. To illustrate the nonintuitive nature of the quantum world, Schrödinger offered a famous thought experiment in which a hypothetical cat was placed in a box with one atom of a radioactive substance attached to a vial of hydrocyanic acid. If the particle degraded within an hour, it would trigger a mechanism that would break the vial and poison the cat. If not, the cat would live. But we could not know which was the case, so there was no choice, scientifically, but to regard the cat as 100 percent alive and 100 percent dead at the same time. This means, as Stephen Hawking has observed with a touch of understandable excitement, that one cannot “predict future events exactly if one cannot even measure the present state of the universe precisely!”

Because of its oddities, many physicists disliked quantum theory, or at least certain aspects of it, and none more so than Einstein. This was more than a little ironic since it was he, in his annus mirabilis of 1905, who had so persuasively explained how photons of light could sometimes behave like particles and sometimes like waves-the notion at the very heart of the new physics. “Quantum theory is very worthy of regard,” he observed politely, but he really didn’t like it. “God doesn’t play dice,” he said.[23]

Einstein couldn’t bear the notion that God could create a universe in which some things were forever unknowable. Moreover, the idea of action at a distance-that one particle could instantaneously influence another trillions of miles away-was a stark violation of the special theory of relativity. This expressly decreed that nothing could outrace the speed of light and yet here were physicists insisting that, somehow, at the subatomic level, information could. (No one, incidentally, has ever explained how the particles achieve this feat. Scientists have dealt with this problem, according to the physicist Yakir Aharanov, “by not thinking about it.”)

Above all, there was the problem that quantum physics introduced a level of untidiness that hadn’t previously existed. Suddenly you needed two sets of laws to explain the behavior of the universe-quantum theory for the world of the very small and relativity for the larger universe beyond. The gravity of relativity theory was brilliant at explaining why planets orbited suns or why galaxies tended to cluster, but turned out to have no influence at all at the particle level. To explain what kept atoms together, other forces were needed, and in the 1930s two were discovered: the strong nuclear force and weak nuclear force. The strong force binds atoms together; it’s what allows protons to bed down together in the nucleus. The weak force engages in more miscellaneous tasks, mostly to do with controlling the rates of certain sorts of radioactive decay.

The weak nuclear force, despite its name, is ten billion billion billion times stronger than gravity, and the strong nuclear force is more powerful still-vastly so, in fact-but their influence extends to only the tiniest distances. The grip of the strong force reaches out only to about 1/100,000 of the diameter of an atom. That’s why the nuclei of atoms are so compacted and dense and why elements with big, crowded nuclei tend to be so unstable: the strong force just can’t hold on to all the protons.

The upshot of all this is that physics ended up with two bodies of laws-one for the world of the very small, one for the universe at large-leading quite separate lives. Einstein disliked that, too. He devoted the rest of his life to searching for a way to tie up these loose ends by finding a grand unified theory, and always failed. From time to time he thought he had it, but it always unraveled on him in the end. As time passed he became increasingly marginalized and even a little pitied. Almost without exception, wrote Snow, “his colleagues thought, and still think, that he wasted the second half of his life.”

Elsewhere, however, real progress was being made. By the mid-1940s scientists had reached a point where they understood the atom at an extremely profound level-as they all too effectively demonstrated in August 1945 by exploding a pair of atomic bombs over Japan.

By this point physicists could be excused for thinking that they had just about conquered the atom. In fact, everything in particle physics was about to get a whole lot more complicated. But before we take up that slightly exhausting story, we must bring another straw of our history up to date by considering an important and salutary tale of avarice, deceit, bad science, several needless deaths, and the final determination of the age of the Earth.

10 GETTING THE LEAD OUT

IN THE LATE 1940s, a graduate student at the University of Chicago named Clair Patterson (who was, first name notwithstanding, an Iowa farm boy by origin) was using a new method of lead isotope measurement to try to get a definitive age for the Earth at last. Unfortunately all his samples came up contaminated-usually wildly so. Most contained something like two hundred times the levels of lead that would normally be expected to occur. Many years would pass before Patterson realized that the reason for this lay with a regrettable Ohio inventor named Thomas Midgley, Jr.

Midgley was an engineer by training, and the world would no doubt have been a safer place if he had stayed so. Instead, he developed an interest in the industrial applications of chemistry. In 1921, while working for the General Motors Research Corporation in Dayton, Ohio, he investigated a compound called tetraethyl lead (also known, confusingly, as lead tetraethyl), and discovered that it significantly reduced the juddering condition known as engine knock.

Even though lead was widely known to be dangerous, by the early years of the twentieth century it could be found in all manner of consumer products. Food came in cans sealed with lead solder. Water was often stored in lead-lined tanks. It was sprayed onto fruit as a pesticide in the form of lead arsenate. It even came as part of the packaging of toothpaste tubes. Hardly a product existed that didn’t bring a little lead into consumers’ lives. However, nothing gave it a greater and more lasting intimacy than its addition to gasoline.

Lead is a neurotoxin. Get too much of it and you can irreparably damage the brain and central nervous system. Among the many symptoms associated with overexposure are blindness, insomnia, kidney failure, hearing loss, cancer, palsies, and convulsions. In its most acute form it produces abrupt and terrifying hallucinations, disturbing to victims and onlookers alike, which generally then give way to coma and death. You really don’t want to get too much lead into your system.

On the other hand, lead was easy to extract and work, and almost embarrassingly profitable to produce industrially-and tetraethyl lead did indubitably stop engines from knocking. So in 1923 three of America’s largest corporations, General Motors, Du Pont, and Standard Oil of New Jersey, formed a joint enterprise called the Ethyl Gasoline Corporation (later shortened to simply Ethyl Corporation) with a view to making as much tetraethyl lead as the world was willing to buy, and that proved to be a very great deal. They called their additive “ethyl” because it sounded friendlier and less toxic than “lead” and introduced it for public consumption (in more ways than most people realized) on February 1, 1923.

Almost at once production workers began to exhibit the staggered gait and confused faculties that mark the recently poisoned. Also almost at once, the Ethyl Corporation embarked on a policy of calm but unyielding denial that would serve it well for decades. As Sharon Bertsch McGrayne notes in her absorbing history of industrial chemistry, Prometheans in the Lab, when employees at one plant developed irreversible delusions, a spokesman blandly informed reporters: “These men probably went insane because they worked too hard.” Altogether at least fifteen workers died in the early days of production of leaded gasoline, and untold numbers of others became ill, often violently so; the exact numbers are unknown because the company nearly always managed to hush up news of embarrassing leakages, spills, and poisonings. At times, however, suppressing the news became impossible, most notably in 1924 when in a matter of days five production workers died and thirty-five more were turned into permanent staggering wrecks at a single ill-ventilated facility.

As rumors circulated about the dangers of the new product, ethyl’s ebullient inventor, Thomas Midgley, decided to hold a demonstration for reporters to allay their concerns. As he chatted away about the company’s commitment to safety, he poured tetraethyl lead over his hands, then held a beaker of it to his nose for sixty seconds, claiming all the while that he could repeat the procedure daily without harm. In fact, Midgley knew only too well the perils of lead poisoning: he had himself been made seriously ill from overexposure a few months earlier and now, except when reassuring journalists, never went near the stuff if he could help it.

Buoyed by the success of leaded gasoline, Midgley now turned to another technological problem of the age. Refrigerators in the 1920s were often appallingly risky because they used dangerous gases that sometimes leaked. One leak from a refrigerator at a hospital in Cleveland, Ohio, in 1929 killed more than a hundred people. Midgley set out to create a gas that was stable, nonflammable, noncorrosive, and safe to breathe. With an instinct for the regrettable that was almost uncanny, he invented chlorofluorocarbons, or CFCs.

Seldom has an industrial product been more swiftly or unfortunately embraced. CFCs went into production in the early 1930s and found a thousand applications in everything from car air conditioners to deodorant sprays before it was noticed, half a century later, that they were devouring the ozone in the stratosphere. As you will be aware, this was not a good thing.

Ozone is a form of oxygen in which each molecule bears three atoms of oxygen instead of two. It is a bit of a chemical oddity in that at ground level it is a pollutant, while way up in the stratosphere it is beneficial, since it soaks up dangerous ultraviolet radiation. Beneficial ozone is not terribly abundant, however. If it were distributed evenly throughout the stratosphere, it would form a layer just one eighth of an inch or so thick. That is why it is so easily disturbed, and why such disturbances don’t take long to become critical.

Chlorofluorocarbons are also not very abundant-they constitute only about one part per billion of the atmosphere as a whole-but they are extravagantly destructive. One pound of CFCs can capture and annihilate seventy thousand pounds of atmospheric ozone. CFCs also hang around for a long time-about a century on average-wreaking havoc all the while. They are also great heat sponges. A single CFC molecule is about ten thousand times more efficient at exacerbating greenhouse effects than a molecule of carbon dioxide-and carbon dioxide is of course no slouch itself as a greenhouse gas. In short, chlorofluorocarbons may ultimately prove to be just about the worst invention of the twentieth century.

Midgley never knew this because he died long before anyone realized how destructive CFCs were. His death was itself memorably unusual. After becoming crippled with polio, Midgley invented a contraption involving a series of motorized pulleys that automatically raised or turned him in bed. In 1944, he became entangled in the cords as the machine went into action and was strangled.

If you were interested in finding out the ages of things, the University of Chicago in the 1940s was the place to be. Willard Libby was in the process of inventing radiocarbon dating, allowing scientists to get an accurate reading of the age of bones and other organic remains, something they had never been able to do before. Up to this time, the oldest reliable dates went back no further than the First Dynasty in Egypt from about 3000 B.C. No one could confidently say, for instance, when the last ice sheets had retreated or at what time in the past the Cro-Magnon people had decorated the caves of Lascaux in France.

Libby’s idea was so useful that he would be awarded a Nobel Prize for it in 1960. It was based on the realization that all living things have within them an isotope of carbon called carbon-14, which begins to decay at a measurable rate the instant they die. Carbon-14 has a half-life-that is, the time it takes for half of any sample to disappear[24]-of about 5,600 years, so by working out how much a given sample of carbon had decayed, Libby could get a good fix on the age of an object-though only up to a point. After eight half-lives, only 1/256 of the original radioactive carbon remains, which is too little to make a reliable measurement, so radiocarbon dating works only for objects up to forty thousand or so years old.

Curiously, just as the technique was becoming widespread, certain flaws within it became apparent. To begin with, it was discovered that one of the basic components of Libby’s formula, known as the decay constant, was off by about 3 percent. By this time, however, thousands of measurements had been taken throughout the world. Rather than restate every one, scientists decided to keep the inaccurate constant. “Thus,” Tim Flannery notes, “every raw radiocarbon date you read today is given as too young by around 3 percent.” The problems didn’t quite stop there. It was also quickly discovered that carbon-14 samples can be easily contaminated with carbon from other sources-a tiny scrap of vegetable matter, for instance, that has been collected with the sample and not noticed. For younger samples-those under twenty thousand years or so-slight contamination does not always matter so much, but for older samples it can be a serious problem because so few remaining atoms are being counted. In the first instance, to borrow from Flannery, it is like miscounting by a dollar when counting to a thousand; in the second it is more like miscounting by a dollar when you have only two dollars to count.

Libby’s method was also based on the assumption that the amount of carbon-14 in the atmosphere, and the rate at which it has been absorbed by living things, has been consistent throughout history. In fact it hasn’t been. We now know that the volume of atmospheric carbon-14 varies depending on how well or not Earth’s magnetism is deflecting cosmic rays, and that that can vary significantly over time. This means that some carbon-14 dates are more dubious than others. This is particularly so with dates just around the time that people first came to the Americas, which is one of the reasons the matter is so perennially in dispute.

Finally, and perhaps a little unexpectedly, readings can be thrown out by seemingly unrelated external factors-such as the diets of those whose bones are being tested. One recent case involved the long-running debate over whether syphilis originated in the New World or the Old. Archeologists in Hull, in the north of England, found that monks in a monastery graveyard had suffered from syphilis, but the initial conclusion that the monks had done so before Columbus’s voyage was cast into doubt by the realization that they had eaten a lot of fish, which could make their bones appear to be older than in fact they were. The monks may well have had syphilis, but how it got to them, and when, remain tantalizingly unresolved.

Because of the accumulated shortcomings of carbon-14, scientists devised other methods of dating ancient materials, among them thermoluminesence, which measures electrons trapped in clays, and electron spin resonance, which involves bombarding a sample with electromagnetic waves and measuring the vibrations of the electrons. But even the best of these could not date anything older than about 200,000 years, and they couldn’t date inorganic materials like rocks at all, which is of course what you need if you wish to determine the age of your planet.

The problems of dating rocks were such that at one point almost everyone in the world had given up on them. Had it not been for a determined English professor named Arthur Holmes, the quest might well have fallen into abeyance altogether.

Holmes was heroic as much for the obstacles he overcame as for the results he achieved. By the 1920s, when Holmes was in the prime of his career, geology had slipped out of fashion-physics was the new excitement of the age-and had become severely underfunded, particularly in Britain, its spiritual birthplace. At Durham University, Holmes was for many years the entire geology department. Often he had to borrow or patch together equipment in order to pursue his radiometric dating of rocks. At one point, his calculations were effectively held up for a year while he waited for the university to provide him with a simple adding machine. Occasionally, he had to drop out of academic life altogether to earn enough to support his family-for a time he ran a curio shop in Newcastle upon Tyne-and sometimes he could not even afford the £5 annual membership fee for the Geological Society.

The technique Holmes used in his work was theoretically straightforward and arose directly from the process, first observed by Ernest Rutherford in 1904, in which some atoms decay from one element into another at a rate predictable enough that you can use them as clocks. If you know how long it takes for potassium-40 to become argon-40, and you measure the amounts of each in a sample, you can work out how old a material is. Holmes’s contribution was to measure the decay rate of uranium into lead to calculate the age of rocks, and thus-he hoped-of the Earth.

But there were many technical difficulties to overcome. Holmes also needed-or at least would very much have appreciated-sophisticated gadgetry of a sort that could make very fine measurements from tiny samples, and as we have seen it was all he could do to get a simple adding machine. So it was quite an achievement when in 1946 he was able to announce with some confidence that the Earth was at least three billion years old and possibly rather more. Unfortunately, he now met yet another formidable impediment to acceptance: the conservativeness of his fellow scientists. Although happy to praise his methodology, many maintained that he had found not the age of the Earth but merely the age of the materials from which the Earth had been formed.

It was just at this time that Harrison Brown of the University of Chicago developed a new method for counting lead isotopes in igneous rocks (which is to say those that were created through heating, as opposed to the laying down of sediments). Realizing that the work would be exceedingly tedious, he assigned it to young Clair Patterson as his dissertation project. Famously he promised Patterson that determining the age of the Earth with his new method would be “duck soup.” In fact, it would take years.

Patterson began work on the project in 1948. Compared with Thomas Midgley’s colorful contributions to the march of progress, Patterson’s discovery of the age of the Earth feels more than a touch anticlimactic. For seven years, first at the University of Chicago and then at the California Institute of Technology (where he moved in 1952), he worked in a sterile lab, making very precise measurements of the lead/uranium ratios in carefully selected samples of old rock.

The problem with measuring the age of the Earth was that you needed rocks that were extremely ancient, containing lead- and uranium-bearing crystals that were about as old as the planet itself-anything much younger would obviously give you misleadingly youthful dates-but really ancient rocks are only rarely found on Earth. In the late 1940s no one altogether understood why this should be. Indeed, and rather extraordinarily, we would be well into the space age before anyone could plausibly account for where all the Earth’s old rocks went. (The answer was plate tectonics, which we shall of course get to.) Patterson, meantime, was left to try to make sense of things with very limited materials. Eventually, and ingeniously, it occurred to him that he could circumvent the rock shortage by using rocks from beyond Earth. He turned to meteorites.

The assumption he made-rather a large one, but correct as it turned out-was that many meteorites are essentially leftover building materials from the early days of the solar system, and thus have managed to preserve a more or less pristine interior chemistry. Measure the age of these wandering rocks and you would have the age also (near enough) of the Earth.

As always, however, nothing was quite as straightforward as such a breezy description makes it sound. Meteorites are not abundant and meteoritic samples not especially easy to get hold of. Moreover, Brown’s measurement technique proved finicky in the extreme and needed much refinement. Above all, there was the problem that Patterson’s samples were continuously and unaccountably contaminated with large doses of atmospheric lead whenever they were exposed to air. It was this that eventually led him to create a sterile laboratory-the world’s first, according to at least one account.

It took Patterson seven years of patient work just to assemble suitable samples for final testing. In the spring of 1953 he traveled to the Argonne National Laboratory in Illinois, where he was granted time on a late-model mass spectrograph, a machine capable of detecting and measuring the minute quantities of uranium and lead locked up in ancient crystals. When at last he had his results, Patterson was so excited that he drove straight to his boyhood home in Iowa and had his mother check him into a hospital because he thought he was having a heart attack.

Soon afterward, at a meeting in Wisconsin, Patterson announced a definitive age for the Earth of 4,550 million years (plus or minus 70 million years)-“a figure that stands unchanged 50 years later,” as McGrayne admiringly notes. After two hundred years of trying, the Earth finally had an age.

His main work done, Patterson now turned his attention to the nagging question of all that lead in the atmosphere. He was astounded to find that what little was known about the effects of lead on humans was almost invariably wrong or misleading-and not surprisingly, he discovered, since for forty years every study of lead’s effects had been funded exclusively by manufacturers of lead additives.

In one such study, a doctor who had no specialized training in chemical pathology undertook a five-year program in which volunteers were asked to breathe in or swallow lead in elevated quantities. Then their urine and feces were tested. Unfortunately, as the doctor appears not to have known, lead is not excreted as a waste product. Rather, it accumulates in the bones and blood-that’s what makes it so dangerous-and neither bone nor blood was tested. In consequence, lead was given a clean bill of health.

Patterson quickly established that we had a lot of lead in the atmosphere-still do, in fact, since lead never goes away-and that about 90 percent of it appeared to come from automobile exhaust pipes, but he couldn’t prove it. What he needed was a way to compare lead levels in the atmosphere now with the levels that existed before 1923, when tetraethyl lead was introduced. It occurred to him that ice cores could provide the answer.

It was known that snowfall in places like Greenland accumulates into discrete annual layers (because seasonal temperature differences produce slight changes in coloration from winter to summer). By counting back through these layers and measuring the amount of lead in each, he could work out global lead concentrations at any time for hundreds, or even thousands, of years. The notion became the foundation of ice core studies, on which much modern climatological work is based.

What Patterson found was that before 1923 there was almost no lead in the atmosphere, and that since that time its level had climbed steadily and dangerously. He now made it his life’s quest to get lead taken out of gasoline. To that end, he became a constant and often vocal critic of the lead industry and its interests.

It would prove to be a hellish campaign. Ethyl was a powerful global corporation with many friends in high places. (Among its directors have been Supreme Court Justice Lewis Powell and Gilbert Grosvenor of the National Geographic Society.) Patterson suddenly found research funding withdrawn or difficult to acquire. The American Petroleum Institute canceled a research contract with him, as did the United States Public Health Service, a supposedly neutral government institution.

As Patterson increasingly became a liability to his institution, the school trustees were repeatedly pressed by lead industry officials to shut him up or let him go. According to Jamie Lincoln Kitman, writing in The Nation in 2000, Ethyl executives allegedly offered to endow a chair at Caltech “if Patterson was sent packing.” Absurdly, he was excluded from a 1971 National Research Council panel appointed to investigate the dangers of atmospheric lead poisoning even though he was by now unquestionably the leading expert on atmospheric lead.

To his great credit, Patterson never wavered or buckled. Eventually his efforts led to the introduction of the Clean Air Act of 1970 and finally to the removal from sale of all leaded gasoline in the United States in 1986. Almost immediately lead levels in the blood of Americans fell by 80 percent. But because lead is forever, those of us alive today have about 625 times more lead in our blood than people did a century ago. The amount of lead in the atmosphere also continues to grow, quite legally, by about a hundred thousand metric tons a year, mostly from mining, smelting, and industrial activities. The United States also banned lead in indoor paint, “forty-four years after most of Europe,” as McGrayne notes. Remarkably, considering its startling toxicity, lead solder was not removed from American food containers until 1993.

As for the Ethyl Corporation, it’s still going strong, though GM, Standard Oil, and Du Pont no longer have stakes in the company. (They sold out to a company called Albemarle Paper in 1962.) According to McGrayne, as late as February 2001 Ethyl continued to contend “that research has failed to show that leaded gasoline poses a threat to human health or the environment.” On its website, a history of the company makes no mention of lead-or indeed of Thomas Midgley-but simply refers to the original product as containing “a certain combination of chemicals.”

Ethyl no longer makes leaded gasoline, although, according to its 2001 company accounts, tetraethyl lead (or TEL as it calls it) still accounted for $25.1 million in sales in 2000 (out of overall sales of $795 million), up from $24.1 million in 1999, but down from $117 million in 1998. In its report the company stated its determination to “maximize the cash generated by TEL as its usage continues to phase down around the world.” Ethyl markets TEL through an agreement with Associated Octel of England.

As for the other scourge left to us by Thomas Midgley, chlorofluorocarbons, they were banned in 1974 in the United States, but they are tenacious little devils and any that you loosed into the atmosphere before then (in your deodorants or hair sprays, for instance) will almost certainly be around and devouring ozone long after you have shuffled off. Worse, we are still introducing huge amounts of CFCs into the atmosphere every year. According to Wayne Biddle, 60 million pounds of the stuff, worth $1.5 billion, still finds its way onto the market every year. So who is making it? We are-that is to say, many of our large corporations are still making it at their plants overseas. It will not be banned in Third World countries until 2010.

Clair Patterson died in 1995. He didn’t win a Nobel Prize for his work. Geologists never do. Nor, more puzzlingly, did he gain any fame or even much attention from half a century of consistent and increasingly selfless achievement. A good case could be made that he was the most influential geologist of the twentieth century. Yet who has ever heard of Clair Patterson? Most geology textbooks don’t mention him. Two recent popular books on the history of the dating of Earth actually manage to misspell his name. In early 2001, a reviewer of one of these books in the journal Nature made the additional, rather astounding error of thinking Patterson was a woman.

At all events, thanks to the work of Clair Patterson by 1953 the Earth at last had an age everyone could agree on. The only problem now was it was older than the universe that contained it.

11 MUSTER MARK’S QUARKS

IN 1911, A British scientist named C. T. R. Wilson was studying cloud formations by tramping regularly to the summit of Ben Nevis, a famously damp Scottish mountain, when it occurred to him that there must be an easier way to study clouds. Back in the Cavendish Lab in Cambridge he built an artificial cloud chamber-a simple device in which he could cool and moisten the air, creating a reasonable model of a cloud in laboratory conditions.

The device worked very well, but had an additional, unexpected benefit. When he accelerated an alpha particle through the chamber to seed his make-believe clouds, it left a visible trail-like the contrails of a passing airliner. He had just invented the particle detector. It provided convincing evidence that subatomic particles did indeed exist.

Eventually two other Cavendish scientists invented a more powerful proton-beam device, while in California Ernest Lawrence at Berkeley produced his famous and impressive cyclotron, or atom smasher, as such devices were long excitingly known. All of these contraptions worked-and indeed still work-on more or less the same principle, the idea being to accelerate a proton or other charged particle to an extremely high speed along a track (sometimes circular, sometimes linear), then bang it into another particle and see what flies off. That’s why they were called atom smashers. It wasn’t science at its subtlest, but it was generally effective.

As physicists built bigger and more ambitious machines, they began to find or postulate particles or particle families seemingly without number: muons, pions, hyperons, mesons, K-mesons, Higgs bosons, intermediate vector bosons, baryons, tachyons. Even physicists began to grow a little uncomfortable. “Young man,” Enrico Fermi replied when a student asked him the name of a particular particle, “if I could remember the names of these particles, I would have been a botanist.”

Today accelerators have names that sound like something Flash Gordon would use in battle: the Super Proton Synchrotron, the Large Electron-Positron Collider, the Large Hadron Collider, the Relativistic Heavy Ion Collider. Using huge amounts of energy (some operate only at night so that people in neighboring towns don’t have to witness their lights fading when the apparatus is fired up), they can whip particles into such a state of liveliness that a single electron can do forty-seven thousand laps around a four-mile tunnel in a second. Fears have been raised that in their enthusiasm scientists might inadvertently create a black hole or even something called “strange quarks,” which could, theoretically, interact with other subatomic particles and propagate uncontrollably. If you are reading this, that hasn’t happened.

Finding particles takes a certain amount of concentration. They are not just tiny and swift but also often tantalizingly evanescent. Particles can come into being and be gone again in as little as 0.000000000000000000000001 second (10^-24). Even the most sluggish of unstable particles hang around for no more than 0.0000001 second (10^-7).

Some particles are almost ludicrously slippery. Every second the Earth is visited by 10,000 trillion trillion tiny, all but massless neutrinos (mostly shot out by the nuclear broilings of the Sun), and virtually all of them pass right through the planet and everything that is on it, including you and me, as if it weren’t there. To trap just a few of them, scientists need tanks holding up to 12.5 million gallons of heavy water (that is, water with a relative abundance of deuterium in it) in underground chambers (old mines usually) where they can’t be interfered with by other types of radiation.

Very occasionally, a passing neutrino will bang into one of the atomic nuclei in the water and produce a little puff of energy. Scientists count the puffs and by such means take us very slightly closer to understanding the fundamental properties of the universe. In 1998, Japanese observers reported that neutrinos do have mass, but not a great deal-about one ten-millionth that of an electron.

What it really takes to find particles these days is money and lots of it. There is a curious inverse relationship in modern physics between the tininess of the thing being sought and the scale of facilities required to do the searching. CERN, the European Organization for Nuclear Research, is like a little city. Straddling the border of France and Switzerland, it employs three thousand people and occupies a site that is measured in square miles. CERN boasts a string of magnets that weigh more than the Eiffel Tower and an underground tunnel over sixteen miles around.

Breaking up atoms, as James Trefil has noted, is easy; you do it each time you switch on a fluorescent light. Breaking up atomic nuclei, however, requires quite a lot of money and a generous supply of electricity. Getting down to the level of quarks-the particles that make up particles-requires still more: trillions of volts of electricity and the budget of a small Central American nation. CERN’s new Large Hadron Collider, scheduled to begin operations in 2005, will achieve fourteen trillion volts of energy and cost something over $1.5 billion to construct.[25]

But these numbers are as nothing compared with what could have been achieved by, and spent upon, the vast and now unfortunately never-to-be Superconducting Supercollider, which began being constructed near Waxahachie, Texas, in the 1980s, before experiencing a supercollision of its own with the United States Congress. The intention of the collider was to let scientists probe “the ultimate nature of matter,” as it is always put, by re-creating as nearly as possible the conditions in the universe during its first ten thousand billionths of a second. The plan was to fling particles through a tunnel fifty-two miles long, achieving a truly staggering ninety-nine trillion volts of energy. It was a grand scheme, but would also have cost $8 billion to build (a figure that eventually rose to $10 billion) and hundreds of millions of dollars a year to run.

In perhaps the finest example in history of pouring money into a hole in the ground, Congress spent $2 billion on the project, then canceled it in 1993 after fourteen miles of tunnel had been dug. So Texas now boasts the most expensive hole in the universe. The site is, I am told by my friend Jeff Guinn of the Fort Worth Star-Telegram, “essentially a vast, cleared field dotted along the circumference by a series of disappointed small towns.”

Since the supercollider debacle particle physicists have set their sights a little lower, but even comparatively modest projects can be quite breathtakingly costly when compared with, well, almost anything. A proposed neutrino observatory at the old Homestake Mine in Lead, South Dakota, would cost $500 million to build-this in a mine that is already dug-before you even look at the annual running costs. There would also be $281 million of “general conversion costs.” A particle accelerator at Fermilab in Illinois, meanwhile, cost $260 million merely to refit.

Particle physics, in short, is a hugely expensive enterprise-but it is a productive one. Today the particle count is well over 150, with a further 100 or so suspected, but unfortunately, in the words of Richard Feynman, “it is very difficult to understand the relationships of all these particles, and what nature wants them for, or what the connections are from one to another.” Inevitably each time we manage to unlock a box, we find that there is another locked box inside. Some people think there are particles called tachyons, which can travel faster than the speed of light. Others long to find gravitons-the seat of gravity. At what point we reach the irreducible bottom is not easy to say. Carl Sagan in Cosmos raised the possibility that if you traveled downward into an electron, you might find that it contained a universe of its own, recalling all those science fiction stories of the fifties. “Within it, organized into the local equivalent of galaxies and smaller structures, are an immense number of other, much tinier elementary particles, which are themselves universes at the next level and so on forever-an infinite downward regression, universes within universes, endlessly. And upward as well.”

For most of us it is a world that surpasses understanding. To read even an elementary guide to particle physics nowadays you must now find your way through lexical thickets such as this: “The charged pion and antipion decay respectively into a muon plus antineutrino and an antimuon plus neutrino with an average lifetime of 2.603 x 10^-8 seconds, the neutral pion decays into two photons with an average lifetime of about 0.8 x 10^-16 seconds, and the muon and antimuon decay respectively into . . .” And so it runs on-and this from a book for the general reader by one of the (normally) most lucid of interpreters, Steven Weinberg.

In the 1960s, in an attempt to bring just a little simplicity to matters, the Caltech physicist Murray Gell-Mann invented a new class of particles, essentially, in the words of Steven Weinberg, “to restore some economy to the multitude of hadrons”-a collective term used by physicists for protons, neutrons, and other particles governed by the strong nuclear force. Gell-Mann’s theory was that all hadrons were made up of still smaller, even more fundamental particles. His colleague Richard Feynman wanted to call these new basic particles partons, as in Dolly, but was overruled. Instead they became known as quarks.

Gell-Mann took the name from a line in Finnegans Wake: “Three quarks for Muster Mark!” (Discriminating physicists rhyme the word with storks, not larks, even though the latter is almost certainly the pronunciation Joyce had in mind.) The fundamental simplicity of quarks was not long lived. As they became better understood it was necessary to introduce subdivisions. Although quarks are much too small to have color or taste or any other physical characteristics we would recognize, they became clumped into six categories-up, down, strange, charm, top, and bottom-which physicists oddly refer to as their “flavors,” and these are further divided into the colors red, green, and blue. (One suspects that it was not altogether coincidental that these terms were first applied in California during the age of psychedelia.)

Eventually out of all this emerged what is called the Standard Model, which is essentially a sort of parts kit for the subatomic world. The Standard Model consists of six quarks, six leptons, five known bosons and a postulated sixth, the Higgs boson (named for a Scottish scientist, Peter Higgs), plus three of the four physical forces: the strong and weak nuclear forces and electromagnetism.

The arrangement essentially is that among the basic building blocks of matter are quarks; these are held together by particles called gluons; and together quarks and gluons form protons and neutrons, the stuff of the atom’s nucleus. Leptons are the source of electrons and neutrinos. Quarks and leptons together are called fermions. Bosons (named for the Indian physicist S. N. Bose) are particles that produce and carry forces, and include photons and gluons. The Higgs boson may or may not actually exist; it was invented simply as a way of endowing particles with mass.

It is all, as you can see, just a little unwieldy, but it is the simplest model that can explain all that happens in the world of particles. Most particle physicists feel, as Leon Lederman remarked in a 1985 PBS documentary, that the Standard Model lacks elegance and simplicity. “It is too complicated. It has too many arbitrary parameters,” Lederman said. “We don’t really see the creator twiddling twenty knobs to set twenty parameters to create the universe as we know it.” Physics is really nothing more than a search for ultimate simplicity, but so far all we have is a kind of elegant messiness-or as Lederman put it: “There is a deep feeling that the picture is not beautiful.”

The Standard Model is not only ungainly but incomplete. For one thing, it has nothing at all to say about gravity. Search through the Standard Model as you will, and you won’t find anything to explain why when you place a hat on a table it doesn’t float up to the ceiling. Nor, as we’ve just noted, can it explain mass. In order to give particles any mass at all we have to introduce the notional Higgs boson; whether it actually exists is a matter for twenty-first-century physics. As Feynman cheerfully observed: “So we are stuck with a theory, and we do not know whether it is right or wrong, but we do know that it is a little wrong, or at least incomplete.”

In an attempt to draw everything together, physicists have come up with something called superstring theory. This postulates that all those little things like quarks and leptons that we had previously thought of as particles are actually “strings”-vibrating strands of energy that oscillate in eleven dimensions, consisting of the three we know already plus time and seven other dimensions that are, well, unknowable to us. The strings are very tiny-tiny enough to pass for point particles.

By introducing extra dimensions, superstring theory enables physicists to pull together quantum laws and gravitational ones into one comparatively tidy package, but it also means that anything scientists say about the theory begins to sound worryingly like the sort of thoughts that would make you edge away if conveyed to you by a stranger on a park bench. Here, for example, is the physicist Michio Kaku explaining the structure of the universe from a superstring perspective: “The heterotic string consists of a closed string that has two types of vibrations, clockwise and counterclockwise, which are treated differently. The clockwise vibrations live in a ten-dimensional space. The counterclockwise live in a twenty-six-dimensional space, of which sixteen dimensions have been compactified. (We recall that in Kaluza’s original five-dimensional, the fifth dimension was compactified by being wrapped up into a circle.)” And so it goes, for some 350 pages.

String theory has further spawned something called “M theory,” which incorporates surfaces known as membranes-or simply “branes” to the hipper souls of the world of physics. I’m afraid this is the stop on the knowledge highway where most of us must get off. Here is a sentence from the New York Times, explaining this as simply as possible to a general audience: “The ekpyrotic process begins far in the indefinite past with a pair of flat empty branes sitting parallel to each other in a warped five-dimensional space. . . . The two branes, which form the walls of the fifth dimension, could have popped out of nothingness as a quantum fluctuation in the even more distant past and then drifted apart.” No arguing with that. No understanding it either. Ekpyrotic, incidentally, comes from the Greek word for “conflagration.”

Matters in physics have now reached such a pitch that, as Paul Davies noted in Nature, it is “almost impossible for the non-scientist to discriminate between the legitimately weird and the outright crackpot.” The question came interestingly to a head in the fall of 2002 when two French physicists, twin brothers Igor and Grickha Bogdanov, produced a theory of ambitious density involving such concepts as “imaginary time” and the “Kubo-Schwinger-Martin condition,” and purporting to describe the nothingness that was the universe before the Big Bang-a period that was always assumed to be unknowable (since it predated the birth of physics and its properties).

Almost at once the Bogdanov paper excited debate among physicists as to whether it was twaddle, a work of genius, or a hoax. “Scientifically, it’s clearly more or less complete nonsense,” Columbia University physicist Peter Woit told the New York Times, “but these days that doesn’t much distinguish it from a lot of the rest of the literature.”

Karl Popper, whom Steven Weinberg has called “the dean of modern philosophers of science,” once suggested that there may not be an ultimate theory for physics-that, rather, every explanation may require a further explanation, producing “an infinite chain of more and more fundamental principles.” A rival possibility is that such knowledge may simply be beyond us. “So far, fortunately,” writes Weinberg in Dreams of a Final Theory, “we do not seem to be coming to the end of our intellectual resources.”

Almost certainly this is an area that will see further developments of thought, and almost certainly these thoughts will again be beyond most of us.

While physicists in the middle decades of the twentieth-century were looking perplexedly into the world of the very small, astronomers were finding no less arresting an incompleteness of understanding in the universe at large.

When we last met Edwin Hubble, he had determined that nearly all the galaxies in our field of view are flying away from us, and that the speed and distance of this retreat are neatly proportional: the farther away the galaxy, the faster it is moving. Hubble realized that this could be expressed with a simple equation, Ho = v/d (where Ho is the constant, v is the recessional velocity of a flying galaxy, and d its distance away from us). Ho has been known ever since as the Hubble constant and the whole as Hubble’s Law. Using his formula, Hubble calculated that the universe was about two billion years old, which was a little awkward because even by the late 1920s it was fairly obvious that many things within the universe-not least Earth itself-were probably older than that. Refining this figure has been an ongoing preoccupation of cosmology.

Almost the only thing constant about the Hubble constant has been the amount of disagreement over what value to give it. In 1956, astronomers discovered that Cepheid variables were more variable than they had thought; they came in two varieties, not one. This allowed them to rework their calculations and come up with a new age for the universe of from 7 to 20 billion years-not terribly precise, but at least old enough, at last, to embrace the formation of the Earth.

In the years that followed there erupted a long-running dispute between Allan Sandage, heir to Hubble at Mount Wilson, and Gérard de Vaucouleurs, a French-born astronomer based at the University of Texas. Sandage, after years of careful calculations, arrived at a value for the Hubble constant of 50, giving the universe an age of 20 billion years. De Vaucouleurs was equally certain that the Hubble constant was 100.[26] This would mean that the universe was only half the size and age that Sandage believed-ten billion years. Matters took a further lurch into uncertainty when in 1994 a team from the Carnegie Observatories in California, using measures from the Hubble space telescope, suggested that the universe could be as little as eight billion years old-an age even they conceded was younger than some of the stars within the universe. In February 2003, a team from NASA and the Goddard Space Flight Center in Maryland, using a new, far-reaching type of satellite called the Wilkinson Microwave Anistropy Probe, announced with some confidence that the age of the universe is 13.7 billion years, give or take a hundred million years or so. There matters rest, at least for the moment.

The difficulty in making final determinations is that there are often acres of room for interpretation. Imagine standing in a field at night and trying to decide how far away two distant electric lights are. Using fairly straightforward tools of astronomy you can easily enough determine that the bulbs are of equal brightness and that one is, say, 50 percent more distant than the other. But what you can’t be certain of is whether the nearer light is, let us say, a 58-watt bulb that is 122 feet away or a 61-watt light that is 119 feet, 8 inches away. On top of that you must make allowances for distortions caused by variations in the Earth’s atmosphere, by intergalactic dust, contaminating light from foreground stars, and many other factors. The upshot is that your computations are necessarily based on a series of nested assumptions, any of which could be a source of contention. There is also the problem that access to telescopes is always at a premium and historically measuring red shifts has been notably costly in telescope time. It could take all night to get a single exposure. In consequence, astronomers have sometimes been compelled (or willing) to base conclusions on notably scanty evidence. In cosmology, as the journalist Geoffrey Carr has suggested, we have “a mountain of theory built on a molehill of evidence.” Or as Martin Rees has put it: “Our present satisfaction [with our state of understanding] may reflect the paucity of the data rather than the excellence of the theory.”

This uncertainty applies, incidentally, to relatively nearby things as much as to the distant edges of the universe. As Donald Goldsmith notes, when astronomers say that the galaxy M87 is 60 million light-years away, what they really mean (“but do not often stress to the general public”) is that it is somewhere between 40 million and 90 million light-years away-not quite the same thing. For the universe at large, matters are naturally magnified. Bearing all that in mind, the best bets these days for the age of the universe seem to be fixed on a range of about 12 billion to 13.5 billion years, but we remain a long way from unanimity.

One interesting recently suggested theory is that the universe is not nearly as big as we thought, that when we peer into the distance some of the galaxies we see may simply be reflections, ghost images created by rebounded light.

The fact is, there is a great deal, even at quite a fundamental level, that we don’t know-not least what the universe is made of. When scientists calculate the amount of matter needed to hold things together, they always come up desperately short. It appears that at least 90 percent of the universe, and perhaps as much as 99 percent, is composed of Fritz Zwicky’s “dark matter”-stuff that is by its nature invisible to us. It is slightly galling to think that we live in a universe that, for the most part, we can’t even see, but there you are. At least the names for the two main possible culprits are entertaining: they are said to be either WIMPs (for Weakly Interacting Massive Particles, which is to say specks of invisible matter left over from the Big Bang) or MACHOs (for MAssive Compact Halo Objects-really just another name for black holes, brown dwarfs, and other very dim stars).

Particle physicists have tended to favor the particle explanation of WIMPs, astrophysicists the stellar explanation of MACHOs. For a time MACHOs had the upper hand, but not nearly enough of them were found, so sentiment swung back toward WIMPs but with the problem that no WIMP has ever been found. Because they are weakly interacting, they are (assuming they even exist) very hard to detect. Cosmic rays would cause too much interference. So scientists must go deep underground. One kilometer underground cosmic bombardments would be one millionth what they would be on the surface. But even when all these are added in, “two-thirds of the universe is still missing from the balance sheet,” as one commentator has put it. For the moment we might very well call them DUNNOS (for Dark Unknown Nonreflective Nondetectable Objects Somewhere).

Recent evidence suggests that not only are the galaxies of the universe racing away from us, but that they are doing so at a rate that is accelerating. This is counter to all expectations. It appears that the universe may not only be filled with dark matter, but with dark energy. Scientists sometimes also call it vacuum energy or, more exotically, quintessence. Whatever it is, it seems to be driving an expansion that no one can altogether account for. The theory is that empty space isn’t so empty at all-that there are particles of matter and antimatter popping into existence and popping out again-and that these are pushing the universe outward at an accelerating rate. Improbably enough, the one thing that resolves all this is Einstein’s cosmological constant-the little piece of math he dropped into the general theory of relativity to stop the universe’s presumed expansion, and called “the biggest blunder of my life.” It now appears that he may have gotten things right after all.

The upshot of all this is that we live in a universe whose age we can’t quite compute, surrounded by stars whose distances we don’t altogether know, filled with matter we can’t identify, operating in conformance with physical laws whose properties we don’t truly understand.

And on that rather unsettling note, let’s return to Planet Earth and consider something that we do understand-though by now you perhaps won’t be surprised to hear that we don’t understand it completely and what we do understand we haven’t understood for long.

12 THE EARTH MOVES

IN ONE OF his last professional acts before his death in 1955, Albert Einstein wrote a short but glowing foreword to a book by a geologist named Charles Hapgood entitled Earth’s Shifting Crust: A Key to Some Basic Problems of Earth Science. Hapgood’s book was a steady demolition of the idea that continents were in motion. In a tone that all but invited the reader to join him in a tolerant chuckle, Hapgood observed that a few gullible souls had noticed “an apparent correspondence in shape between certain continents.” It would appear, he went on, “that South America might be fitted together with Africa, and so on. . . . It is even claimed that rock formations on opposite sides of the Atlantic match.”

Mr. Hapgood briskly dismissed any such notions, noting that the geologists K. E. Caster and J. C. Mendes had done extensive fieldwork on both sides of the Atlantic and had established beyond question that no such similarities existed. Goodness knows what outcrops Messrs. Caster and Mendes had looked at, beacuse in fact many of the rock formations on both sides of the Atlantic are the same-not just very similar but the same.

This was not an idea that flew with Mr. Hapgood, or many other geologists of his day. The theory Hapgood alluded to was one first propounded in 1908 by an amateur American geologist named Frank Bursley Taylor. Taylor came from a wealthy family and had both the means and freedom from academic constraints to pursue unconventional lines of inquiry. He was one of those struck by the similarity in shape between the facing coastlines of Africa and South America, and from this observation he developed the idea that the continents had once slid around. He suggested-presciently as it turned out-that the crunching together of continents could have thrust up the world’s mountain chains. He failed, however, to produce much in the way of evidence, and the theory was considered too crackpot to merit serious attention.

In Germany, however, Taylor’s idea was picked up, and effectively appropriated, by a theorist named Alfred Wegener, a meteorologist at the University of Marburg. Wegener investigated the many plant and fossil anomalies that did not fit comfortably into the standard model of Earth history and realized that very little of it made sense if conventionally interpreted. Animal fossils repeatedly turned up on opposite sides of oceans that were clearly too wide to swim. How, he wondered, did marsupials travel from South America to Australia? How did identical snails turn up in Scandinavia and New England? And how, come to that, did one account for coal seams and other semi-tropical remnants in frigid spots like Spitsbergen, four hundred miles north of Norway, if they had not somehow migrated there from warmer climes?

Wegener developed the theory that the world’s continents had once come together in a single landmass he called Pangaea, where flora and fauna had been able to mingle, before the continents had split apart and floated off to their present positions. All this he put together in a book called Die Entstehung der Kontinente und Ozeane, or The Origin of Continents and Oceans, which was published in German in 1912 and-despite the outbreak of the First World War in the meantime-in English three years later.

Because of the war, Wegener’s theory didn’t attract much notice at first, but by 1920, when he produced a revised and expanded edition, it quickly became a subject of discussion. Everyone agreed that continents moved-but up and down, not sideways. The process of vertical movement, known as isostasy, was a foundation of geological beliefs for generations, though no one had any good theories as to how or why it happened. One idea, which remained in textbooks well into my own school days, was the baked apple theory propounded by the Austrian Eduard Suess just before the turn of the century. This suggested that as the molten Earth had cooled, it had become wrinkled in the manner of a baked apple, creating ocean basins and mountain ranges. Never mind that James Hutton had shown long before that any such static arrangement would eventually result in a featureless spheroid as erosion leveled the bumps and filled in the divots. There was also the problem, demonstrated by Rutherford and Soddy early in the century, that Earthly elements hold huge reserves of heat-much too much to allow for the sort of cooling and shrinking Suess suggested. And anyway, if Suess’s theory was correct then mountains should be evenly distributed across the face of the Earth, which patently they were not, and of more or less the same ages; yet by the early 1900s it was already evident that some ranges, like the Urals and Appalachians, were hundreds of millions of years older than others, like the Alps and Rockies. Clearly the time was ripe for a new theory. Unfortunately, Alfred Wegener was not the man that geologists wished to provide it.

For a start, his radical notions questioned the foundations of their discipline, seldom an effective way to generate warmth in an audience. Such a challenge would have been painful enough coming from a geologist, but Wegener had no background in geology. He was a meteorologist, for goodness sake. A weatherman-a German weatherman. These were not remediable deficiencies.

And so geologists took every pain they could think of to dismiss his evidence and belittle his suggestions. To get around the problems of fossil distributions, they posited ancient “land bridges” wherever they were needed. When an ancient horse named Hipparion was found to have lived in France and Florida at the same time, a land bridge was drawn across the Atlantic. When it was realized that ancient tapirs had existed simultaneously in South America and Southeast Asia a land bridge was drawn there, too. Soon maps of prehistoric seas were almost solid with hypothesized land bridges-from North America to Europe, from Brazil to Africa, from Southeast Asia to Australia, from Australia to Antarctica. These connective tendrils had not only conveniently appeared whenever it was necessary to move a living organism from one landmass to another, but then obligingly vanished without leaving a trace of their former existence. None of this, of course, was supported by so much as a grain of actual evidence-nothing so wrong could be-yet it was geological orthodoxy for the next half century.

Even land bridges couldn’t explain some things. One species of trilobite that was well known in Europe was also found to have lived on Newfoundland-but only on one side. No one could persuasively explain how it had managed to cross two thousand miles of hostile ocean but then failed to find its way around the corner of a 200-mile-wide island. Even more awkwardly anomalous was another species of trilobite found in Europe and the Pacific Northwest but nowhere in between, which would have required not so much a land bridge as a flyover. Yet as late as 1964 when the Encyclopaedia Britannica discussed the rival theories, it was Wegener’s that was held to be full of “numerous grave theoretical difficulties.”

To be sure, Wegener made mistakes. He asserted that Greenland is drifting west by about a mile a year, which is clearly nonsense. (It’s more like half an inch.) Above all, he could offer no convincing explanation for how the landmasses moved about. To believe in his theory you had to accept that massive continents somehow pushed through solid crust, like a plow through soil, without leaving any furrow in their wake. Nothing then known could plausibly explain what motored these massive movements.

It was Arthur Holmes, the English geologist who did so much to determine the age of the Earth, who suggested a possible way. Holmes was the first scientist to understand that radioactive warming could produce convection currents within the Earth. In theory these could be powerful enough to slide continents around on the surface. In his popular and influential textbook Principles of Physical Geology, first published in 1944, Holmes laid out a continental drift theory that was in its fundamentals the theory that prevails today. It was still a radical proposition for the time and widely criticized, particularly in the United States, where resistance to drift lasted longer than elsewhere. One reviewer there fretted, without any evident sense of irony, that Holmes presented his arguments so clearly and compellingly that students might actually come to believe them.

Elsewhere, however, the new theory drew steady if cautious support. In 1950, a vote at the annual meeting of the British Association for the Advancement of Science showed that about half of those present now embraced the idea of continental drift. (Hapgood soon after cited this figure as proof of how tragically misled British geologists had become.) Curiously, Holmes himself sometimes wavered in his conviction. In 1953 he confessed: “I have never succeeded in freeing myself from a nagging prejudice against continental drift; in my geological bones, so to speak, I feel the hypothesis is a fantastic one.”

Continental drift was not entirely without support in the United States. Reginald Daly of Harvard spoke for it, but he, you may recall, was the man who suggested that the Moon had been formed by a cosmic impact, and his ideas tended to be considered interesting, even worthy, but a touch too exuberant for serious consideration. And so most American academics stuck to the belief that the continents had occupied their present positions forever and that their surface features could be attributed to something other than lateral motions.

Interestingly, oil company geologists had known for years that if you wanted to find oil you had to allow for precisely the sort of surface movements that were implied by plate tectonics. But oil geologists didn’t write academic papers; they just found oil.

There was one other major problem with Earth theories that no one had resolved, or even come close to resolving. That was the question of where all the sediments went. Every year Earth’s rivers carried massive volumes of eroded material-500 million tons of calcium, for instance-to the seas. If you multiplied the rate of deposition by the number of years it had been going on, it produced a disturbing figure: there should be about twelve miles of sediments on the ocean bottoms-or, put another way, the ocean bottoms should by now be well above the ocean tops. Scientists dealt with this paradox in the handiest possible way. They ignored it. But eventually there came a point when they could ignore it no longer.

In the Second World War, a Princeton University mineralogist named Harry Hess was put in charge of an attack transport ship, the USS Cape Johnson. Aboard this vessel was a fancy new depth sounder called a fathometer, which was designed to facilitate inshore maneuvers during beach landings, but Hess realized that it could equally well be used for scientific purposes and never switched it off, even when far out at sea, even in the heat of battle. What he found was entirely unexpected. If the ocean floors were ancient, as everyone assumed, they should be thickly blanketed with sediments, like the mud on the bottom of a river or lake. But Hess’s readings showed that the ocean floor offered anything but the gooey smoothness of ancient silts. It was scored everywhere with canyons, trenches, and crevasses and dotted with volcanic seamounts that he called guyots after an earlier Princeton geologist named Arnold Guyot. All this was a puzzle, but Hess had a war to take part in, and put such thoughts to the back of his mind.

After the war, Hess returned to Princeton and the preoccupations of teaching, but the mysteries of the seafloor continued to occupy a space in his thoughts. Meanwhile, throughout the 1950s oceanographers were undertaking more and more sophisticated surveys of the ocean floors. In so doing, they found an even bigger surprise: the mightiest and most extensive mountain range on Earth was-mostly-underwater. It traced a continuous path along the world’s seabeds, rather like the stitching on a baseball. If you began at Iceland, you could follow it down the center of the Atlantic Ocean, around the bottom of Africa, and across the Indian and Southern Oceans, below Australia; there it angled across the Pacific as if making for Baja California before shooting up the west coast of the United States to Alaska. Occasionally its higher peaks poked above the water as an island or archipelago-the Azores and Canaries in the Atlantic, Hawaii in the Pacific, for instance-but mostly it was buried under thousands of fathoms of salty sea, unknown and unsuspected. When all its branches were added together, the network extended to 46,600 miles.

A very little of this had been known for some time. People laying ocean-floor cables in the nineteenth century had realized that there was some kind of mountainous intrusion in the mid-Atlantic from the way the cables ran, but the continuous nature and overall scale of the chain was a stunning surprise. Moreover, it contained physical anomalies that couldn’t be explained. Down the middle of the mid-Atlantic ridge was a canyon-a rift-up to a dozen miles wide for its entire 12,000-mile length. This seemed to suggest that the Earth was splitting apart at the seams, like a nut bursting out of its shell. It was an absurd and unnerving notion, but the evidence couldn’t be denied.

Then in 1960 core samples showed that the ocean floor was quite young at the mid-Atlantic ridge but grew progressively older as you moved away from it to the east or west. Harry Hess considered the matter and realized that this could mean only one thing: new ocean crust was being formed on either side of the central rift, then being pushed away from it as new crust came along behind. The Atlantic floor was effectively two large conveyor belts, one carrying crust toward North America, the other carrying crust toward Europe. The process became known as seafloor spreading.

When the crust reached the end of its journey at the boundary with continents, it plunged back into the Earth in a process known as subduction. That explained where all the sediment went. It was being returned to the bowels of the Earth. It also explained why ocean floors everywhere were so comparatively youthful. None had ever been found to be older than about 175 million years, which was a puzzle because continental rocks were often billions of years old. Now Hess could see why. Ocean rocks lasted only as long as it took them to travel to shore. It was a beautiful theory that explained a great deal. Hess elaborated his ideas in an important paper, which was almost universally ignored. Sometimes the world just isn’t ready for a good idea.

Meanwhile, two researchers, working independently, were making some startling findings by drawing on a curious fact of Earth history that had been discovered several decades earlier. In 1906, a French physicist named Bernard Brunhes had found that the planet’s magnetic field reverses itself from time to time, and that the record of these reversals is permanently fixed in certain rocks at the time of their birth. Specifically, tiny grains of iron ore within the rocks point to wherever the magnetic poles happen to be at the time of their formation, then stay pointing in that direction as the rocks cool and harden. In effect they “remember” where the magnetic poles were at the time of their creation. For years this was little more than a curiosity, but in the 1950s Patrick Blackett of the University of London and S. K. Runcorn of the University of Newcastle studied the ancient magnetic patterns frozen in British rocks and were startled, to say the very least, to find them indicating that at some time in the distant past Britain had spun on its axis and traveled some distance to the north, as if it had somehow come loose from its moorings. Moreover, they also discovered that if you placed a map of Europe’s magnetic patterns alongside an American one from the same period, they fit together as neatly as two halves of a torn letter. It was uncanny.

Their findings were ignored too.

It finally fell to two men from Cambridge University, a geophysicist named Drummond Matthews and a graduate student of his named Fred Vine, to draw all the strands together. In 1963, using magnetic studies of the Atlantic Ocean floor, they demonstrated conclusively that the seafloors were spreading in precisely the manner Hess had suggested and that the continents were in motion too. An unlucky Canadian geologist named Lawrence Morley came up with the same conclusion at the same time, but couldn’t find anyone to publish his paper. In what has become a famous snub, the editor of the Journal of Geophysical Research told him: “Such speculations make interesting talk at cocktail parties, but it is not the sort of thing that ought to be published under serious scientific aegis.” One geologist later described it as “probably the most significant paper in the earth sciences ever to be denied publication.”

At all events, mobile crust was an idea whose time had finally come. A symposium of many of the most important figures in the field was convened in London under the auspices of the Royal Society in 1964, and suddenly, it seemed, everyone was a convert. The Earth, the meeting agreed, was a mosaic of interconnected segments whose various stately jostlings accounted for much of the planet’s surface behavior.

The name “continental drift” was fairly swiftly discarded when it was realized that the whole crust was in motion and not just the continents, but it took a while to settle on a name for the individual segments. At first people called them “crustal blocks” or sometimes “paving stones.” Not until late 1968, with the publication of an article by three American seismologists in the Journal of Geophysical Research, did the segments receive the name by which they have since been known: plates. The same article called the new science plate tectonics.

Old ideas die hard, and not everyone rushed to embrace the exciting new theory. Well into the 1970s, one of the most popular and influential geological textbooks, The Earth by the venerable Harold Jeffreys, strenuously insisted that plate tectonics was a physical impossibility, just as it had in the first edition way back in 1924. It was equally dismissive of convection and seafloor spreading. And in Basin and Range, published in 1980, John McPhee noted that even then one American geologist in eight still didn’t believe in plate tectonics.

Today we know that Earth’s surface is made up of eight to twelve big plates (depending on how you define big) and twenty or so smaller ones, and they all move in different directions and at different speeds. Some plates are large and comparatively inactive, others small but energetic. They bear only an incidental relationship to the landmasses that sit upon them. The North American plate, for instance, is much larger than the continent with which it is associated. It roughly traces the outline of the continent’s western coast (which is why that area is so seismically active, because of the bump and crush of the plate boundary), but ignores the eastern seaboard altogether and instead extends halfway across the Atlantic to the mid-ocean ridge. Iceland is split down the middle, which makes it tectonically half American and half European. New Zealand, meanwhile, is part of the immense Indian Ocean plate even though it is nowhere near the Indian Ocean. And so it goes for most plates.

The connections between modern landmasses and those of the past were found to be infinitely more complex than anyone had imagined. Kazakhstan, it turns out, was once attached to Norway and New England. One corner of Staten Island, but only a corner, is European. So is part of Newfoundland. Pick up a pebble from a Massachusetts beach, and its nearest kin will now be in Africa. The Scottish Highlands and much of Scandinavia are substantially American. Some of the Shackleton Range of Antarctica, it is thought, may once have belonged to the Appalachians of the eastern U.S. Rocks, in short, get around.

The constant turmoil keeps the plates from fusing into a single immobile plate. Assuming things continue much as at present, the Atlantic Ocean will expand until eventually it is much bigger than the Pacific. Much of California will float off and become a kind of Madagascar of the Pacific. Africa will push northward into Europe, squeezing the Mediterranean out of existence and thrusting up a chain of mountains of Himalayan majesty running from Paris to Calcutta. Australia will colonize the islands to its north and connect by some isthmian umbilicus to Asia. These are future outcomes, but not future events. The events are happening now. As we sit here, continents are adrift, like leaves on a pond. Thanks to Global Positioning Systems we can see that Europe and North America are parting at about the speed a fingernail grows-roughly two yards in a human lifetime. If you were prepared to wait long enough, you could ride from Los Angeles all the way up to San Francisco. It is only the brevity of lifetimes that keeps us from appreciating the changes. Look at a globe and what you are seeing really is a snapshot of the continents as they have been for just one-tenth of 1 percent of the Earth’s history.

Earth is alone among the rocky planets in having tectonics, and why this should be is a bit of a mystery. It is not simply a matter of size or density-Venus is nearly a twin of Earth in these respects and yet has no tectonic activity. It is thought-though it is really nothing more than a thought-that tectonics is an important part of the planet’s organic well-being. As the physicist and writer James Trefil has put it, “It would be hard to believe that the continuous movement of tectonic plates has no effect on the development of life on earth.” He suggests that the challenges induced by tectonics-changes in climate, for instance-were an important spur to the development of intelligence. Others believe the driftings of the continents may have produced at least some of the Earth’s various extinction events. In November of 2002, Tony Dickson of Cambridge University in England produced a report, published in the journal Science, strongly suggesting that there may well be a relationship between the history of rocks and the history of life. What Dickson established was that the chemical composition of the world’s oceans has altered abruptly and vigorously throughout the past half billion years and that these changes often correlate with important events in biological history-the huge outburst of tiny organisms that created the chalk cliffs of England’s south coast, the sudden fashion for shells among marine organisms during the Cambrian period, and so on. No one can say what causes the oceans’ chemistry to change so dramatically from time to time, but the opening and shutting of ocean ridges would be an obvious possible culprit.

At all events, plate tectonics not only explained the surface dynamics of the Earth-how an ancient Hipparion got from France to Florida, for example-but also many of its internal actions. Earthquakes, the formation of island chains, the carbon cycle, the locations of mountains, the coming of ice ages, the origins of life itself-there was hardly a matter that wasn’t directly influenced by this remarkable new theory. Geologists, as McPhee has noted, found themselves in the giddying position that “the whole earth suddenly made sense.”

But only up to a point. The distribution of continents in former times is much less neatly resolved than most people outside geophysics think. Although textbooks give confident-looking representations of ancient landmasses with names like Laurasia, Gondwana, Rodinia, and Pangaea, these are sometimes based on conclusions that don’t altogether hold up. As George Gaylord Simpson observes in Fossils and the History of Life, species of plants and animals from the ancient world have a habit of appearing inconveniently where they shouldn’t and failing to be where they ought.

The outline of Gondwana, a once-mighty continent connecting Australia, Africa, Antarctica, and South America, was based in large part on the distribution of a genus of ancient tongue fern called Glossopteris, which was found in all the right places. However, much later Glossopteris was also discovered in parts of the world that had no known connection to Gondwana. This troubling discrepancy was-and continues to be-mostly ignored. Similarly a Triassic reptile called Lystrosaurus has been found from Antarctica all the way to Asia, supporting the idea of a former connection between those continents, but it has never turned up in South America or Australia, which are believed to have been part of the same continent at the same time.

There are also many surface features that tectonics can’t explain. Take Denver. It is, as everyone knows, a mile high, but that rise is comparatively recent. When dinosaurs roamed the Earth, Denver was part of an ocean bottom, many thousands of feet lower. Yet the rocks on which Denver sits are not fractured or deformed in the way they would be if Denver had been pushed up by colliding plates, and anyway Denver was too far from the plate edges to be susceptible to their actions. It would be as if you pushed against the edge of a rug hoping to raise a ruck at the opposite end. Mysteriously and over millions of years, it appears that Denver has been rising, like baking bread. So, too, has much of southern Africa; a portion of it a thousand miles across has risen nearly a mile in 100 million years without any known associated tectonic activity. Australia, meanwhile, has been tilting and sinking. Over the past 100 million years as it has drifted north toward Asia, its leading edge has sunk by some six hundred feet. It appears that Indonesia is very slowly drowning, and dragging Australia down with it. Nothing in the theories of tectonics can explain any of this.

Alfred Wegener never lived to see his ideas vindicated. On an expedition to Greenland in 1930, he set out alone, on his fiftieth birthday, to check out a supply drop. He never returned. He was found a few days later, frozen to death on the ice. He was buried on the spot and lies there yet, but about a yard closer to North America than on the day he died.

Einstein also failed to live long enough to see that he had backed the wrong horse. In fact, he died at Princeton, New Jersey, in 1955 before Charles Hapgood’s rubbishing of continental drift theories was even published.

The other principal player in the emergence of tectonics theory, Harry Hess, was also at Princeton at the time, and would spend the rest of his career there. One of his students was a bright young fellow named Walter Alvarez, who would eventually change the world of science in a quite different way.

As for geology itself, its cataclysms had only just begun, and it was young Alvarez who helped to start the process.