THOSE forty years, that is from the end of the nineteenth century to the outbreak of the Second World War, were a wonderful time for physicists to be alive. Both experimental physicists and theoreticians had their phases of triumph, and it is instructive to notice how the balance swung. There was a long record of experimental discoveries beginning with elucidation of the radiations emitted from radioactive elements and evidence that most of an atom’s mass lay in a central nucleus. Rutherford and Chadwick’s disintegration of atoms by particles from radioactive sources led on to disintegration of atoms by controlled means by Cockcroft and Walton. Meanwhile there was identification of further sub-atomic particles – neutrons and positive electrons. And in 1938 the most fateful experiment of all, the splitting of some uranium atoms with an emission of particles which could lead to further splitting, with the possibility of a chain reaction and the release of huge amounts of energy.
Through most of this period, the dominant figure was Ernest Rutherford who was born in 1871. As has been said, he ranks with Faraday among British experimental physicists. As a man, he was wildly different from Faraday – exuberant, outgoing, not noticeably modest or unassuming. He was taken at face value, a simple face value, by most of the people round him. Internally, he was not so simple. There were deep layers of diffidence concealed beneath that robust and noisy façade. He was a prey to nerves. He found it hard to manage an overweighted nature. Kapitsa, one of the most gifted of his pupils, an engineering-physicist of genius in the high Russian tradition, and in addition equipped with psychological observation and insight, seems to have been the only member of Rutherford’s scientific entourage who understood him well. Kapitsa’s letters to his mother in Leningrad, dating from the time he first came to England to work with Rutherford, have recently been published in the Soviet Union. Within a few days Kapitsa was writing, ‘The Professor is a deceptive character. They [the English] think he is a hearty colonial. Not so. He is a man of immense temperament. He is given to uncontrollable excitement. His moods fluctuate violently. It will need great vigilance if I am going to obtain, and keep, his high opinion.’
About the only item true in the stereotype of Rutherford is that he was a colonial. His father was a Scottish immigrant to New Zealand, who managed after scraping a living, doing odd jobs, to become a small farmer and a kind of general utility man, employing one or two workmen and doing anything in the way of domestic repairs. He seems to have had a good deal of technical ingenuity.
Rutherford knew nothing in the way of privilege. New Zealand was a remote province. He received a good education, however, rather on the Scottish model. He was top of his school in all subjects, being very far from the dumb-ox kind of scientist who occasionally turns up. But when he came to England on a scholarship he felt an outsider who didn’t know the rules. There were a good many chips on those heavy shoulders. He couldn’t get along with English intellectual chit-chat, and insisted on behaving like a country boy who had never read a book (actually he was very widely read) with people of about one-hundredth of his cultivation, not to say intelligence.
He was a great man, and a good one. He didn’t like being outfaced, though, by people who had learned tricks denied him. He wasn’t comfortable in the company of well-trained theoreticians. Of course he could have mastered theoretical physics, or anything else in science, but some of those shoulder chips got in the way. When he was Cavendish professor, Cambridge became the world centre of experimental physics, but it didn’t rank with Copenhagen and Göttingen in theory – except for the accidental occurrence of a young theoretical physicist of great genius, Paul Dirac. His appearance had nothing to do with Rutherford; that the divide in Cambridge between theoretical and experimental physics was sharp, did have something to do with Rutherford.
As a physicist, he had extraordinary intuition. He seems scarcely ever to have tried a problem which wouldn’t go. If any scientist had a nose for, to use Medawar’s phrase, ‘the solution of the possible’, Rutherford had. His attack was simple and direct, or rather he saw his way, through the hedges of complication, to a method which was the simplest and most direct.
An example is the most dramatic event of his career, the experiments by which he proved the existence of the atomic nucleus. The Curies had shown that radium emits various kinds of ‘radiation’, and one of these was now known to consist of a stream of electrically charged particles. These ‘alpha particles’ were identical to helium atoms with their electrons removed; but they originated not from helium gas but sprang spontaneously from the radium atoms as they disintegrated.
Even though atomic disintegration was still little understood, Rutherford saw these high-speed alpha particles as useful projectiles. He intercepted them with a thin sheet of gold foil, to see what happened as they passed through. If atoms were diffuse spheres of electrical charge, as Thomson had imagined, then most of the alpha particles should have gone straight through; a few should be deflected slightly. But some of the alpha particles bounced straight back again. It was like firing artillery shells at a piece of tissue paper, and getting some of them returning in the direction of the gun.
Rutherford could only explain this by postulating that these alpha particles were hitting small, massive concentrations within the atoms. He thus concluded that most of an atom’s mass resided in a minute, positively charged nucleus at the centre, while the electrons went around the outside – very much like the planets orbiting the massive sun. Most of the atom was just empty space. If an atom were expanded to the size of the dome of St Paul’s Cathedral, virtually all its mass would lie within a central nucleus no larger than an orange. The large majority of alpha particles passed the atoms’ emptiness and carried on through the foil; but just occasionally one would hit a nucleus head-on, and rebound along the way it had come.
Positive, like all Rutherford’s physics. He said that he knew it was convincing, and maintained that he was completely surprised. One wonders if he hadn’t had a secret inkling. He was superlatively good at making predictions about nature.
It is hard to think of a prediction of his which didn’t come off. He predicted the existence of an electrically neutral particle within the atomic nucleus, which was duly proved when Chadwick discovered the neutron in 1932. He predicted the splitting of atoms by accelerated protons, duly achieved by Cockcroft that same year. He made just one negative prediction: as late as 1933, he announced that the energies in the atom were unlikely ever to be used. That apart, he was almost always right. His Cavendish ‘boys’ as he called them – men as gifted as Chadwick, Kapitsa, Cockcroft, Blackett (all Nobel prize winners), Oliphant, Dee, half a dozen others – tended to think that, though he might be overpowering or deafeningly noisy, he was next door to infallible.
That was his kind of paternal leadership. His own greatest individual work wasn’t done at Cambridge at all. With singular folly, Cambridge didn’t try to keep the young Rutherford – possibly because the place wasn’t big enough to hold both him and his seniors. He went off to a professorship at Montreal. American universities bid for him, better talent-spotters than Cambridge, but at the time America wasn’t a major force in the scientific world, and Rutherford returned to England, after a touching and deliberate resignation by the head of the physics department at Manchester, Arthur Schuster, who thought that Rutherford must at any cost be preserved for this country. It was at Manchester that Rutherford proved the nuclear structure of the atom.
It is instructive to remember how little money was spent on these great scientific researches. Faraday’s apparatus (some still preserved in the Royal Institution) was humble, knocked up in the laboratory. Things hadn’t changed much by Rutherford’s time. His experiments were built with the help of one laboratory technician, or if he were feeling well-financed, perhaps two. There was no engineering. All was home made. The old phrase was ‘string and sealing wax’, and it is not far from the truth. The Cavendish was a great experimental laboratory, but it would look like a badly equipped high school compared with the big physics institutions of today. It was not until trained engineers such as Kapitsa and Cockcroft became active that the Cavendish knew any approach to big physics. Rutherford marvelled and cheered them on, but sometimes thought that it might be overdone.
Until the Second World War, there was little industrial support for physicists. Chemists had been looked after by the chemical industry for many years: other industries had been peculiarly obtuse in not seeing any conceivable use for physicists. Young men in the l930s, with doctorates and good research to their credit, considered themselves lucky to get decent jobs in schools. A few years later, in the war, they were being snatched up as the rarest and most valuable of all human commodities.
It seems strange now that the Cavendish at its peak should have stayed so remote from industry. With the harsh wind of approaching war, however, Cockcroft, the Cavendish all-purpose functionary, was set to indoctrinate selected young men in the latest military prospect – what was later called by the American name of radar, and was the most successful British scientific weapon in the Hitler war. Few unobtrusive steps have paid off better. By the by, that happened in the same university which contemporary opinion seems to believe was devoted entirely to espionage.
Rutherford and his colleagues had little to do with money. It seems to have bored Rutherford himself about as much as academic philosophy. He was a remarkably unmercenary man. He could have earned large fees as a consultant. He would have thought that a ludicrous waste of time. As a professor at Montreal he was paid £500 a year. At Manchester and Cambridge he got about £1600, a good academic salary for the period, but he never earned more than that. When he died, he left almost exactly the amount of his Nobel prize, which at that time was something like £7,000.
In that brilliant period, an even rarer character was leaving his mark on world physics. This was Albert Einstein. He was born in 1879, and thus was eight years younger than Rutherford. When he was in his twenties, people were talking of him as the new Copernicus. A little later, it wasn’t unusual or extravagant to say that here, for the first and only time, was someone in the class of Newton.
Einstein’s greatest work touched only remotely on the new particle physics. His Theory of Relativity – actually in two parts, Special Relativity and General Relativity – made him rightly world-famous. But it dealt not with the small-scale structure of matter, but the largest scales of space, time and speed. Ironically enough, relativity was at the time so controversial that Einstein was not awarded his Nobel prize for the greatest of his theories, but for some early work on the effect of light on metal surfaces. His explanation of this photo-electric effect, however, did form an important basis on which later particle physicists could build when they came to describe atoms in terms of quantum theory – of which more later.
Einstein was the most independent of all great scientists, relying with absolute confidence on his own solitary thoughts. He had set out to understand all aspects of the natural world: space, time, the unity and harmony of the entire world picture. He had set out to find the most universal of universal laws. He did so.
This makes him sound portentous. In his own personality, he wasn’t, not in the least. He was cheerful, unaffected and amiable to everyone, and extremely witty. He was the best company of all the great physicists. In his serious moments, and there were many as the political scene darkened, he did speak from a depth of moral experience. He was as certain of his moral insight as of his physical insight. He wanted to do his best for his fellow humans, but he was the least sentimental of men. He recognized no collective loyalties except to the human race. He had renounced his German nationality at the age of sixteen, one of the most astonishing – and revealing – acts that any boy has ever done. But he wasn’t really a boy – he was full of animal spirits and vigour, but his nature was formed at a very early age.
He had no use for the minute differences which divide men from one another. It is true that, though he didn’t believe in Judaism any more than he believed in any other religion, he preserved a special feeling for his own Jewish people. Conversely, while he was given all honours in Germany and the conditions for his major achievement, he does seem to have had a special negative feeling for Germans. In later life he did not admit to having made a real German friend – outside German Jews. That was odd, in one so benevolent and so removed from ordinary human rancour. But, though he was as much above pettiness of spirit as anyone, he was human after all.
Einstein was not deeply interested in the details of particle physics. Max Planck had shown in 1900 that light is emitted in distinct ‘packets’ or quanta of energy (a concept essential for the later theory of modern physics, though undervalued by some historians of science), and Einstein’s 1905 paper on the photo-electric effect added the significant point that light remains in these packets as it travels. But after that he went off, single-minded, in his own cosmic thoughts. No one has ever been able to think more obsessively, and for longer, on a single issue. It was a supreme gift for his kind of abstract creation – perhaps for any other creation – and one he shared, to the same degree, with his greatest predecessor, Newton.
Of course, he read what was being discovered about the structure of the atom. He said later, in his benign manner, that he had been impressed by the beauty of Rutherford’s experiments, done with the simplest of means, and going straight for physical reality. Einstein wished, so he said, that he had been able to write something about Rutherford in his own work, but there hadn’t been any adequate connection.
That may not have been more than a handsome gesture to another great figure. Rutherford tried to reciprocate, announcing in a speech that the General Theory of Relativity, irrespective of whether it was valid, was a magnificent work of art.
The qualification in that tribute has an eloquence of its own.
Rutherford knew perfectly well that the General Theory was valid, but he didn’t believe that it added much to his own idea of physics. The two men never became close. They made speeches together when in 1933 Rutherford was leading a campaign to find aid for Jewish scientific refugees. But Rutherford didn’t make an attempt to attract Einstein to Cambridge. It wasn’t necessary: Einstein, as everyone knew, was receiving offers from all over America, Britain, Europe, and in his casual good-natured manner was tending to accept them all.
The trouble between the two was caused, at least in part, by the disparity in the treatment of the great experimentalists as contrasted with that of the great theoreticians.
In terms of popular esteem, experimentalists felt, and still feel, as Rutherford did with his usual horse-power, that they got an unfair deal. The names of theoreticians survived in intellectual currency: the names of experimentalists didn’t. Einstein provided the most vivid illustration.
Before he was forty, with the General Theory still waiting for a conclusive experimental test, Einstein was the most famous scientist in the world – perhaps more famous than any scientist would be again. Whereas Rutherford had nothing but celebrity amongst scientists themselves. He might have taken the first great steps in elucidating the structure of the atom, but he wasn’t a national figure, not celebrated as a film star in the way that Einstein was. Experimentalists did all the ground work, and without the results of experiments there wouldn’t be any theory. Yet no experimentalist had ever caught the popular imagination. Inventors had, occasionally, witness Edison and Marconi, but never scientists doing experiments to discover the fundamentals of the universe.
It seemed mysterious. It was as though popular opinion had somehow realized that science, the whole great enterprise, was a collective activity in which individual personalities, and individual achievements, didn’t much matter. If one practitioner didn’t make a discovery this year, someone else would come along and make it next year. And that was true at the height of scientific creativity. If Rutherford hadn’t proved the existence of the atom’s nucleus in 1911, no one doubts that someone would have performed the same experiments within a decade, probably less than that.
A great scientist adds his own brick to the cumulative edifice. There are few human beings who have the capacity to be great scientists. It was once estimated that only one person in a million could do first-class original work, and that was drawing the line far below the Rutherfords. Nevertheless, if one scientist doesn’t add his appropriate brick, another will. H J G Moseley, one of the rising stars of English science, was killed at Gallipoli, aged twenty-seven. He had had time to leave an indelible mark on the text books: if he had lived, he would have been one of the very great. And yet, though he would have done splendid things, those things in due course were inexorably done by others, and the sand smoothed down over Moseley’s absence as though he had never been.
Much of those sobering thoughts applies to theoreticians also – but not quite so bleakly. First of all, great theoreticians are even rarer animals than great experimentalists. That kind of conceptual skill is one of the most uncommon of all human gifts. Perhaps one in a hundred million is born with the potential to be something like Clerk Maxwell, and even that guess may be over-optimistic. As a consequence, their creations are not quite so quickly replaceable. The most incisive tribute to Einstein was made by Dirac, who doesn’t inflate his words. Dirac said first that if Einstein hadn’t published the Special Theory of Relativity in 1905, someone else would have done it within an extremely short time, five years or less. Several people, we now know, were already very near, Lorentz, Minkowski, Poincaré: that is exactly like the standard position in experimental physics.
But, Dirac went on, the General Theory, which Einstein published in 1916, is an entirely different matter. Without it, it is likely that we should still be waiting for the theory today. That is one of the most striking things ever said of one great scientist by another.
There was no injustice in Einstein’s transcending fame. Still it is possible that the mana of his personality encouraged it. He was so unlike the rest of humankind. Amusing, more than a bit of a deliberate clown; unshakable, supremely confident both in scientific and moral judgements. When he felt deeply, he was rather like an Old Testament prophet, or else a benign deity being patient with human stupidity and worse – but also like a benign deity who had considerable physical resemblance to a handsome and inspired golliwog. No one who knew him expected to meet anything like that again: and they were right.
Whether Rutherford felt anything like that about him, we don’t know. In spite of the aura around Einstein, his scientific thinking was as direct as Rutherford’s own. But it might not have reconciled Rutherford to theoreticians in general, and to this one theoretician in particular, to be told so.