Modern Mind: An Intellectual History of the 20th Century (51 page)

A new science, dendrochronology, had been born, and Pueblo Bonito was the first classical problem it helped solve. Douglass’s research had begun in 1913, but not until 1928–9 did he feel able to announce his findings to the world. At that point, by overlapping trees of different ages felled at different times, he had an unbroken sequence of rings in southwest America going back first to
ALL
1300, then to
ALL 700.
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The sequence revealed that there had been a severe drought, which lasted from
ALL
1276 to 1299 and explained why there had been a vast migration at that time by Pueblo Indians, a puzzle which had baffled archaeologists for centuries.

These discoveries placed yet more of man’s history on an evolutionary ladder, with ever more specific time frames. The evolution of writing, of religions, of law, and even of building all began to slot into place in the 1920s, making history and prehistory more and more comprehensible as one linked story. Even the familiar events of the Bible appeared to fit into the emerging sequence of events. Such a view had its dangers, of course. Order could be imposed where there may have been none, and complex processes could be oversimplified. Many people were fascinated by scientific discovery and found the
new narrative satisfying, but others were disturbed by what they took to be further ‘disenchantment’ of the world, the removal of mystery. That was one reason why a very short book, published in 1931, had the impact that it did.

Herbert Butterfield was still only twenty-six when, as a young don at Peterhouse, Cambridge, he published
The Whig Interpretation of History
and made his reputation.
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Controversial as it was, and although he was not really concerned with evolution as such, his argument concerned ‘the friends and enemies of progress’ and was nonetheless therefore a useful corrective to the emerging consensus. Butterfield exploded the teleological view of history – that it is essentially a straight line leading to the present. To Butterfield, the idea of ‘progress’ was suspect, as was the notion that in any conflict there were always the good guys who won and the bad guys who lost. The particular example he used was the way the Renaissance led to the Reformation and then on to the contemporary world. The prevailing view, what he called the Whig view, was to see a straight line from the essentially Catholic Renaissance to the Protestant Reformation to the modern world with all its freedoms, as a result of which many attributed to Luther the intention of promoting greater liberty.
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Butterfield argued that this view assumed ‘a false continuity in events’: the Whig historian ‘likes to imagine religious liberty issuing beautifully out of Protestantism when in reality it emerges painfully and grudgingly out of something quite different, out of the tragedy of the post-Reformation world.’
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The motive for this habit on the part of historians was, said Butterfield, contemporary politics – in its broadest sense. The present-day historian’s enthusiasm for democracy or freedom of thought or the liberal tradition led him to conclude that people in the past were working toward these goals.
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One consequence of this tendency, Butterfield thought, was that the Whig historian was overfond of making moral judgements on the past: ‘For him the voice of posterity is the voice of God and the historian is the voice of posterity. And it is typical of him that he tends to regard himself as the judge when by his methods and his equipment he is fitted only to be the detective.’
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This fashion for moral judgements leads the Whig historian into another mistake, that more evil is due to conscious sin than to unconscious error.
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Butterfield was uneasy with such a stance. He offered the alternative view – that all history could do was approach its subjects in more and more detail, and with less and less abridgement. No moral judgements are necessary for him because it is impossible to get within the minds of people of bygone ages and because the great quarrels of history have not been between two parties of which one was ‘good’ and the other ‘evil’ but between opposing groups (not necessarily two in number) who had rival ideas about where they wanted events, and society, to go. To judge backward from the present imposes a modern mindset on events which cannot be understood in that way.
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Butterfield’s ideas acted as a check on the growth of evolutionary thought, but only a check. As time went by, and more results came in, the evidence amassed for one story was overwhelming. Progress was a word less and less used, but evolution went from strength to strength, invading even history itself.
The discoveries of the 1920s pushed forward the idea that a complete history of mankind might one day be possible. This expanding vision was further fuelled by parallel developments in physics.

The period from 1919, when Ernest Rutherford first split the atom, to 1932, when his student James Chadwick discovered the neutron, was a golden decade for physics. Barely a year went by without some momentous breakthrough. At that stage, America was far from being the world leader in physics it has since become. All the seminal work of the golden decade was carried out in one of three places in Europe: the Cavendish Laboratory in Cambridge, England; Niels Bohr’s Institute of Theoretical Physics in Copenhagen; and the old university town of Göttingen, near Marburg in Germany.

For Mark Oliphant, one of Rutherford’s protégés in the 1920s, the main hallway of the Cavendish, where the director’s office was, consisted of ‘uncarpeted floor boards, dingy varnished pine doors and stained, plastered walls, indifferently lit by a skylight with dirty glass.
¹
For C. P. Snow, however, who also trained there and described the lab in his first novel,
The Search,
the paint and the varnish and the dirty glass went unremarked. ‘I shall not easily forget those Wednesday meetings in the Cavendish. For me they were the essence of all the
personal
excitement in science; they were romantic, if you like, and not on the plane of the highest experience I was soon to know [of scientific discovery]; but week after week I went away through the raw nights, with east winds howling from the fens down the old streets, full of a glow that I had seen and heard and been close to the leaders of the greatest movement in the world.’ Rutherford, who followed Maxwell as director of the Cavendish in 1919, evidently agreed. At a meeting of the British Association in 1923 he startled colleagues by suddenly shouting out, ‘We are living in the heroic age of physics!’
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In some ways, Rutherford himself – now a rather florid man, with a moustache and a pipe that was always going out – embodied in his own person that heroic age. During World War I, particle physics had been on hold, more or less. Officially, Rutherford was working for the Admiralty, researching submarine detection. But he carried on research when his duties allowed. And in the last year of war, in April 1919, just as Arthur Eddington was preparing his trip to West Africa to test Einstein’s predictions, Rutherford sent off a paper that, had he done nothing else, would earn him a place in history. Not that you would have known it from the paper’s title: ‘An Anomalous Effect in
Nitrogen.’ As was usual in Rutherford’s experiments, the apparatus was simple to the point of being crude: a small glass tube inside a sealed brass box fitted at one end with a zinc-sulphide scintillation screen. The brass box was filled with nitrogen and then through the glass tube was passed a source of alpha particles – helium nuclei – given off by radon, the radioactive gas of radium. The excitement came when Rutherford inspected the activity on the zinc-sulphide screen: the scintillations were indistinguishable from those obtained from hydrogen. How could that be, since there was no hydrogen in the system? This led to the famously downbeat sentence in the fourth part of Rutherford’s paper: ‘From the results so far obtained it is difficult to avoid the conclusion that the longrange atoms arising from collision of [alpha] particles with nitrogen are not nitrogen atoms but probably atoms of hydrogen…. If this be the case, we must conclude that the nitrogen atom is disintegrated.’ The newspapers were not so cautious. Sir Ernest Rutherford, they shouted, had
split the atom.
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He himself realised the importance of his work. His experiments had drawn him away, temporarily, from antisubmarine research. He defended himself to the overseers’ committee: ‘If, as I have reason to believe, I have disintegrated the nucleus of the atom, this is of greater significance than the war.’
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In a sense, Rutherford had finally achieved what the old alchemists had been aiming for, transmuting one element into another, nitrogen into oxygen and hydrogen. The mechanism whereby this artificial transmutation (the first ever) was achieved was clear: an alpha particle, a helium nucleus, has an atomic weight of 4. When it was bombarded on to a nitrogen atom, with an atomic weight of 14, it displaced a hydrogen nucleus (to which Rutherford soon gave the name proton). The arithmetic therefore became: 4+14–1=17, the oxygen isotope, O
¹⁷
.
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The significance of the discovery, apart from the philosophical one of the transmutability of nature, lay in the new way it enabled the nucleus to be studied. Rutherford and Chadwick immediately began to probe other light atoms to see if they behaved in the same way. It turned out that they did – boron, fluorine, sodium, aluminum, phosphorus, all had nuclei that could be probed: they were not just solid matter but had a structure. All this work on light elements took five years, but then there was a problem. The heavier elements were, by definition, characterised by outer shells of many electrons that constituted a much stronger electrical barrier and would need a stronger source of alpha particles if they were to be penetrated. For James Chadwick and his young colleagues at the Cavendish, the way ahead was clear – they needed to explore means of accelerating particles to higher velocities. Rutherford wasn’t convinced, preferring simple experimental tools. But elsewhere, especially in America, physicists realised that one way ahead lay with particle accelerators.

Between 1924 and 1932, when Chadwick finally isolated the neutron, there were no breakthroughs in nuclear physics. Quantum physics, on the other hand, was an entirely different matter. Niels Bohr’s Institute of Theoretical Physics opened in Copenhagen on 18 January 1921. The land had been given
by the city, appropriately enough next to some soccer fields (Niels and his brother, Harald, were both excellent players).
⁶
The large house, on four floors, shaped like an ‘L,’ contained a lecture hall, library, and laboratories (strange for an institute
of theoretical
physics), as well as a table-tennis table, where Bohr also shone. ‘His reactions were very fast and accurate,’ says Otto Frisch, ‘and he had tremendous will power and stamina. In a way those qualities characterised his scientific work as well.’
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Bohr became a Danish hero a year later when he won the Nobel Prize. Even the king wanted to meet him. But in fact the year was dominated by something even more noteworthy – Bohr’s final irrevocable linking of chemistry and physics. In 1922 Bohr showed how atomic structure was linked to the periodic table of elements drawn up by Dmitri Ivanovich Mendeléev, the nineteenth-century Russian chemist. In his first breakthrough, just before World War I, Bohr had explained how electrons orbit the nucleus only in certain formations, and how this helped explain the characteristic spectra of light emitted by the crystals of different substances. This idea of natural orbits also married atomic structure to Max Planck’s notion of quanta. Bohr now went on to argue that successive orbital shells of electrons could contain only a precise number of electrons. He introduced the idea that elements that behave in a similar way chemically do so because they have a similar arrangement of electrons in their outer shells, which are the ones most used in chemical reactions. For example, he compared barium and radium, which are both alkaline earths but have very different atomic weights and occupy, respectively, the fifty-sixth and eighty-eighth place in the periodic table. Bohr explained this by showing that barium, atomic weight 137.34, has electron shells filled successively by 2, 8,18, 18, 8, and 2 (=56) electrons. Radium, atomic weight 226, has on the other hand electron shells filled successively by 2, 8, 18, 32, 18, 8, and 2 (=88) electrons.
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Besides explaining their position on the periodic table, the fact that the outer shell of each element has two electrons means barium and radium are chemically similar despite their considerable other differences. As Einstein said, ‘This is the highest form of musicality in the sphere of thought.’
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During the 1920s the centre of gravity of physics – certainly of quantum physics – shifted to Copenhagen, largely because of Bohr. A big man in every sense, he was intent on expressing himself accurately, if painfully slowly, and forcing others to do so too. He was generous, avuncular, completely devoid of those instincts for rivalry that can so easily sour relations. But the success of Copenhagen also had to do with the fact that Denmark was a small country, neutral, where national rivalries of the Americans, British, French, Germans, Russians, and Italians could be forgotten. Among the sixty-three physicists of renown who studied at Copenhagen in the 1920s were Paul Dirac (British), Werner Heisenberg (German), and Lev Landau (Russian).
¹⁰

There was also the Swiss-Austrian, Wolfgang Pauli. In 1924 Pauli was a pudgy twenty-three-year-old, prone to depression when scientific problems defeated him. One problem in particular had set him prowling the streets of the Danish capital. It was something that vexed Bohr too, and it arose from the fact that no one, just then, understood why all the electrons in orbit around the nucleus didn’t just crowd in on the inner shell. This is what should have
happened, with the electrons emitting energy in the form of light. What was known by now, however, was that each shell of electrons was arranged so that the inner shell always contains just one orbit, whereas the next shell out contains four. Pauli’s contribution was to show that no orbit could contain more than two electrons. Once it had two, an orbit was ‘full,’ and other electrons were excluded, forced to the next orbit out.
¹¹
This meant that the inner shell (one orbit) could not contain more than two electrons, and that the next shell out (four orbits) could not contain more than eight. This became known as Pauli’s exclusion principle, and part of its beauty lay in the way it expanded Bohr’s explanation of chemical behaviour.
¹²
Hydrogen, for example, with one electron in the first orbit, is chemically active. Helium, however, with two electrons in the first orbit (i.e., that orbit is ‘full’ or ‘complete’), is virtually inert. To underline the point further, lithium, the third element, has two electrons in the inner shell and one in the next, and is chemically very active. Neon, however, which has ten electrons, two in the inner shell (filling it) and eight in the four outer orbits of the second shell (again filling those orbits), is also inert.
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So together Bohr and Pauli had shown how the chemical properties of elements are determined not only by the number of electrons the atom possesses but also by the dispersal of those electrons through the orbital shells.

The next year, 1925, was the high point of the golden age, and the centre of activity moved for a time to Göttingen. Before World War I, British and American students regularly went to Germany to complete their studies, and Göttingen was a frequent stopping-off place. Moreover, it had held on to its prestige and status better than most in the Weimar years. Bohr gave a lecture there in 1922 and was taken to task by a young student who corrected a point in his argument. Bohr, being Bohr, hadn’t minded. ‘At the end of the discussion he came over to me and asked me to join him that afternoon on a walk over the Hain Mountain,’
Werner Heisenberg
wrote later. ‘My real scientific career only began that afternoon.’
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In fact it was more than a stroll, for Bohr invited the young Bavarian to Copenhagen. Heisenberg didn’t feel ready to go for two years, but Bohr was just as welcoming after the delay, and they immediately set about tackling yet another problem of quantum theory, what Bohr called
‘correspondence.’
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This stemmed from the observation that, at low frequencies, quantum physics and classical physics came together. But how could that be? According to quantum theory, energy – like light – was emitted in tiny packets; according to classical physics, it was emitted continuously. Heisenberg returned to Göttingen enthused but also confused. And Heisenberg hated confusion as much as Pauli did. And so when, toward the end of May 1925, he suffered one of his many attacks of hay fever, he took two weeks’ holiday in Heligoland, a narrow island off the German coast in the North Sea, where there was next to no poden. An excellent pianist who could also recite huge tracts of Goethe, Heisenberg was very fit (he liked climbing), and he cleared his head with long walks and bracing dips in the sea.
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The idea that came to Heisenberg in that cold, fresh environment was the first example of what came to be called quantum weirdness. Heisenberg took the view that we should stop trying to visualise what goes on inside an atom, as it is impossible to observe
directly something so small.
¹⁷
All we can do is measure its properties. And so, if something is measured as continuous at one point, and discrete at another, that is the way of reality. If the two measurements exist, it makes no sense to say that they disagree: they are just measurements.

This was Heisenberg’s central insight, but in a hectic three weeks he went further, developing a method of mathematics, known as matrix math, originating from an idea by David Hilbert, in which the measurements obtained are grouped in a two-dimensional table of numbers where two matrices can be multiplied together to give another matrix.
¹⁸
In Heisenberg’s scheme, each atom would be represented by one matrix, each ‘rule’ by another. If one multiplied the ‘sodium matrix’ by the ‘spectral line matrix,’ the result should give the matrix of wavelengths of sodium’s spectral lines. To Heisenberg’s, and Bohr’s, great satisfaction, it did; ‘For the first time, atomic structure had a genuine, though very surprising, mathematical base.’
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Heisenberg called his creation/discovery quantum mechanics.