by Bill Bryson
3 Einstein was honoured, somewhat vaguely, “for services to theoretical physics.” He had to wait sixteen years, until 1921, to receive the award—quite a long time, all things considered, but nothing at all compared with Frederick Reines, who detected the neutrino in 1957 but wasn’t honoured with a Nobel until 1995, thirty-eight years later, or the German Ernst Ruska, who invented the electron microscope in 1932 and received his Nobel Prize in 1986, more than half a century after the fact. Since Nobel Prizes are never awarded posthumously, longevity can be as important a factor as ingenuity in securing one.
4 How c came to be the symbol for the speed of light is something of a mystery, but David Bodanis suggests it probably came from the Latin celeritas, meaning swiftness. The relevant volume of the Oxford English Dictionary, compiled a decade before Einstein’s theory, recognizes c as a symbol for many things, from carbon to cricket, but makes no mention of it as a symbol for light or swiftness.
5 Named for Johann Christian Doppler, an Austrian physicist, who first noticed the effect in 1842. Briefly, what happens is that as a moving object approaches a stationary one its sound waves become bunched up as they cram up against whatever device is receiving them (your ears, say), just as you would expect of anything that is being pushed from behind towards an immobile object. This bunching is perceived by the listener as a kind of pinched and elevated sound (the yee). As the sound source passes, the sound waves spread out and lengthen, causing the pitch to drop abruptly (the yummm).
Atomium, centrepiece of the 1958 Brussels World Exposition and reminder of a time when humanity’s newfound mastery of atoms promised a happy future for all. Rising to a height of 102 metres, Atomium was intended to reflect the crystal lattice structure of iron. (credit 9.1)
THE MIGHTY ATOM
While Einstein and Hubble were productively unravelling 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 everything. 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 0 degrees Celsius, one cubic centimetre 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 centimetre you see around you. Think how many cubic centimetres 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 themselves, however, go on practically for ever. 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 mathematical 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 millimetre, 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 micro-organisms. A typical paramecium, for instance—a tiny, single-celled, freshwater creature—is about 2 microns wide, 0.002 millimetres, 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 12 metres across. However, if you wanted to see the atoms in the same drop, you would have to make the drop 24 kilometres 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 millimetre. 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 that millimetre line above 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 make 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 Chapter 7.
Dalton was born in 1766 on the edge of the Lake District, near Cockermouth, to a family of poor and 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, whence he scarcely stirred 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. Colour 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.
Paramecia—one of them caught in the process of dividing—swim in a drop of water, accompanied by smaller protozoans called biflagellates. Though invisible to the naked eye, such organisms are gigantic compared with atoms. (credit 9.2)
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 re
lative 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 1. He believed also that water consisted of seven parts of oxygen to one of hydrogen, and so he gave oxygen an atomic weight of 7. 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 16, not 7—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 travelled 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 honours, 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 cortège stretched for two miles. His entry in the Dictionary of National Biography is one of the longest, rivalled in length among nineteenth-century men of science only by those of Darwin and Lyell.
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. Such was the scepticism with which the existence of atoms was viewed 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.
John Dalton, the English chemist and thinker who became famous when he developed the theory that all matter is made of tiny indivisible particles called atoms. (credit 9.3)
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 great Austrian physicist Wolfgang Pauli’s wife 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 his award of the Nobel Prize in 1908 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—possibly the very first—to see that the power inherent in the atom could, if harnessed, make bombs powerful enough to “make this old world vanish in smoke.”
Some unusual personal effects of John Dalton: a letter, a hank of hair and his eyeballs, dissected. Dalton suffered from colour blindness and thought that his eyes might yield clues to the condition. He bequeathed them to a physician friend, who failed to find anything significant in them. (credit 9.4)
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, 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.1 It was a singularly eventful period in science. In the year of Rutherford’s arrival in Cambridge, Wilhelm Roentgen discovered X-rays at the University of Würzburg in Germany; 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, in 1953, James Watson and Francis Crick would discover the structure of DNA at the Cavendish.
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 he 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, and after three years there, feeling he was going nowhere, he took a post at McGill University in Montreal, where 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 fitted 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) fire
d ionized helium atoms, or alpha particles, at a sheet of gold foil.2 To Rutherford’s astonishment, some of the particles bounced back. It was as if, he said, he had fired a 15-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 centre. This was a most gratifying discovery, but it presented one immediate problem. By all the laws of conventional physics, atoms shouldn’t therefore exist.
The New Zealand-born physicist Ernest Rutherford (facing camera) strikes a thoughtful pose in the Cavendish Laboratory at Cambridge in 1926. Rutherford, who won a Nobel Prize for his work on atomic structure in 1908, became one of many Nobel laureates to work at the Cavendish during its years of pre-eminence. (credit 9.5)
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 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.)