In Our Time

by Melvyn Bragg

  In case it appeared that every scientist outside the Soviet Union was querying Lysenko, Steve Jones stressed that he did have support. Ideology was not behind this, although a lot of scientists had sympathy for left-wing ideas. He said that J. B. S. Haldane, a famous geneticist and a towering genius in science, went along with Lysenko until 1956 and almost wished that Lysenko was right. And the industrial programme behind the Urals was very successful, which may have coloured perceptions of agriculture. The fundamental problem was that the agricultural scientists did not accept the truth of what they found. Sometimes, findings mean that you have to reconsider everything you believed, and that did not happen.

  STEVE JONES: We may not like it but we have to swallow it. And that was the problem, they didn’t like it so they didn’t swallow it. And that really was the difference between Soviet biology and western biology.

  Lysenko was being presented as the great new leader of a new kind of agrobiology, with which the Soviet Union was to transform itself and the world. People in the west had seen the ruination of their economy in the 1930s with the Great Depression and, as Robert Service said, they willed themselves into thinking that this way of planning everything from the centre was a better way of running things than the rather messy, chaotic contours of capitalism. Stalin was very pleased with a speech Lysenko gave in 1948, denouncing Mendel and Darwin. Even Khrushchev was well disposed towards him.

  CATHERINE MERRIDALE: When Khrushchev was party secretary in the Ukraine, he’d adopted one of Lysenko’s earlier schemes for chicken breeding. And so he was …

  MELVYN BRAGG: What was that?

  CATHERINE MERRIDALE: Don’t ask … it was what he fed them on. And the problem with Khrushchev is that he was already one of the previous regime. So to announce that the emperor has no clothes would actually be to leave himself naked, too.

  Lysenko did persuade Khrushchev that he could still be the great head of science, even while there was clearly something interesting going on in the west with genetics and, by then, Watson and Crick had won the Nobel Prize in 1962 ‘for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material’. It was very hard to let Lysenko go. Quietly, meanwhile, in Novosibirsk, 1,750 miles east of Moscow, scientists were taking a growing interest in genetics. In his lifetime, Catherine Merridale said, he was not made the figure of vilification that others were in the Soviet period. At the end of his career, he was left to work at a little farm on the Lenin Hills outside Moscow, which was eventually shut down, but he was not attacked as he had attacked others.

  PAULI’S EXCLUSION PRINCIPLE

  In 1925, Wolfgang Pauli made a decisive contribution to atomic theory through his discovery of a new and fundamental law of nature, the exclusion principle or, as it became known, the Pauli principle. It asserts that no two electrons in an atom can be at the same time in the same state or configuration. It was groundbreaking as it explained a huge range of phenomena, from the chemical behaviour of the elements to why matter is stable, and, for this, he won the Nobel Prize in Physics in 1945. Pauli also correctly predicted the existence of the neutrino and astonished and intrigued his peers. He was called the ‘conscience of physics’, yet he was fascinated by mysticism, alchemy and dreams, which he explored with the psychoanalyst Carl Jung.

  With Melvyn to discuss Pauli and his exclusion principle were: Frank Close, fellow emeritus at Exeter College, Oxford; Michela Massimi, professor of philosophy of science at the University of Edinburgh; and Graham Farmelo, fellow of Churchill College, Cambridge.

  By 1900, the year Pauli was born, scientists knew that matter was made of elements and that the elements were all made of atoms. Starting at that point, Frank Close proceeded to introduce us as simply as possible to ideas of some complexity. It was also known at that time that scientists could order the atoms of the different elements by mass, where hydrogen was the lightest, then helium, and, finally, the heaviest naturally occurring element, uranium. While each element had some unique properties, there were some common features that kept recurring. For example, some elements are inert, such as neon, argon and helium, while others are very active.

  FRANK CLOSE: And they noticed that, when you looked at this ordering, the inert elements appeared regularly and either side of them would be an element that was very active, like sodium or chlorine, for example. And this periodic recurrence of common properties became known as the periodic table.

  This was an observable, empirical rule that worked but nobody knew why. Another thing about elements that was surprising was that, if the atoms were heated up, they would emit light but not the whole rainbow. Passing the light through a kind of spectrograph, they would make a bar code of individual colours, which became known as spectra. Again, nobody knew why atoms were doing this.

  Just before Pauli’s birth, scientists learned that atoms had some inner structure. The electron was discovered, which was negatively charged, and the atoms were soon shown to consist of these electrons orbiting a central nucleus with positive charge. The problem with that was that it was impossible, according to Newton’s laws of physics, as electrons whirling around a nucleus, held together by the electrical force, should spiral into the nucleus in a fraction of a second. There would be no atoms, and that was a great paradox that had to be solved, Frank Close said.

  Niels Bohr (1885–1962) had an insight into what was really going on with atoms. He deduced that the electrons were restricted to what he called ‘orbits’ and were not free to travel anywhere. Using maths, he said that, with the rotary motion, as they whirl around, the angular momentum has to be a multiple of an integer, a whole number times some fundamental quantity, which became the quantum.

  FRANK CLOSE: Electrons can’t go anywhere – they have to have one of these magic values. And this gives rise to an analogy that it was like having a ladder with rungs on: if you hold the ladder vertically, you can be on a high rung with high energy or a low rung with low energy but you can’t be between rungs. So the electrons had to be on a rung somewhere. And they could jump from a high rung to a low rung.

  If, metaphorically, the electrons did jump from a high rung to a low rung, then the energy that they lost was emitted as light of a characteristic colour. These ideas emerged around 1913, when Pauli was a schoolboy.

  Pauli came from an affluent family of Czech-Austrian origin, Michela Massimi told us, and his father went to a school in Prague with a son of the great physicist and philosopher Ernst Mach (1838–1916). Mach was the author of The Science of Mechanics in which he famously criticised Newton’s ideas of space and time and he was hugely influential, with Einstein regarding Mach as a precursor of relativity theory. He was also a philosopher who influenced the Vienna Circle of logical empiricists with his well-known anti-metaphysical attitude. Pauli’s father had converted to Catholicism, married Bertha Camilla Schütz, a prominent Austrian woman who had written on the French Revolution. When Pauli was born, Mach was invited to become his godfather. The story goes, that many years later, Pauli said, jokingly, that, because Mach was such a great influence on him, he was baptised not so much Catholic but anti-metaphysical, a line of reasoning that remained for the rest of his career.

  When he was eighteen, Pauli went to Munich to study with the leading spectroscopist of the time (someone who studies the interaction between matter and electromagnetic radiation), Arnold Sommerfeld (1868–1951).

  MICHELA MASSIMI: Arnold Sommerfeld was so impressed by the mathematical ability of the young Pauli that, when Albert Einstein declined the invitation to write an encyclopaedia article on relativity theory, he asked his student, his eighteen-year-old Pauli, whether he wanted to write the article. And so here we have a young university student producing an incredible encyclopaedia article on relativity theory.

  The result was published in 1921 and was welcomed as an outstanding achievement by some of the great mathematicians of the time. Beyond writing a simple survey of the theory, Pauli pointe
d out problems in relativity theory, such as the problem of the structure of matter, to which he himself was to turn. He spent a period in Copenhagen with Niels Bohr, and, in 1928, he got his first full professorship at the Swiss Federal Institute of Technology in Zurich, or ETH, although the story is that this was only after that position had been declined by his rival, Werner Heisenberg.

  There was another quantum nettle to grasp when understanding Pauli’s contributions.

  MELVYN BRAGG: Can you tell us about Pauli’s idea of two-valuedness in (I was reading that carefully) two-valuedness in electronics?

  GRAHAM FARMELO: This was perhaps his greatest contribution. We wind the clock back to about 1924. He’s in Hamburg, he’s a night owl, visiting the red-light district, having loveless sex in the evening, showing up very late in the mornings, thinking very deeply about these spectra that Frank was talking about …

  MELVYN BRAGG: All human life is here.

  The spectra questions were those mentioned above, where atoms were making jumps from rung to rung, and the experimenters were trying to make sense of the discrete frequencies of light. This was a big problem.

  GRAHAM FARMELO: The thing that Pauli did so brilliantly was concentrate on one particular set of problems, and that was what’s called the alkali element, lithium, sodium, potassium and so on. Now the reason these were special was that those particular elements, people had worked out, consist of shells, which you can imagine very crudely as a kind of sphere, like a soccer ball of electrons with one electron around the outside, which you call a valence electron.

  Graham Farmelo told us that, if the atoms, mentioned above, were subjected to a magnetic field, that could alter the frequency of the spectral lines and that was puzzling to scientists. Pauli said that he could account for those spectral lines if the electron did not just have ‘three quantum numbers that specified the state of the electron’. But, if that outer electron, the valence electron, had what he called a two-valuedness, that accounted for the spectral lines and also for the number of electrons that were in that shell.

  MELVYN BRAGG: So what is this two-valuedness?

  GRAHAM FARMELO: Well, he didn’t know.

  MELVYN BRAGG: I love it when you say things like that.

  People asked Pauli what he meant, and he was very cautious in his replies. Graham Farmelo continued, ‘He wrote it in his very, very clear way that it was due to a particular non-classically describable two-valuedness of the valence electron.’ He was saying that there was something doubled about that but he was not prepared to say what it was. We moved on, much like Pauli’s peers, in hope of clarification later.

  Melvyn asked Frank Close to explain the exclusion principle, the idea for which Pauli is best remembered. He started by saying that this related to electrons, one of the fundamental constituents of all atoms, in that, if there is an electron already in an atom in a place, you cannot put another electron in there, it is excluded. As an example, if Frank Close were to rap the table, his hand would not pass through the table because the electrons in the outer rim of his knuckle were trying to occupy a state that was already being occupied by an electron in the wood of the table, so it was excluded. This requirement that electrons have to go in special places, as occupied states are already excluded, gives rise to structure and to the different chemical natures of the atoms. Returning to the ladder analogy, we can start on the bottom rung with hydrogen, which has a single electron, and the rungs higher up grow wider to accommodate more electrons. The bottom rung, the simplest one, can only be occupied by two, which Frank Close said related to the two-valuedness that Graham Farmelo was mentioning.

  FRANK CLOSE: One electron, that’s hydrogen; two electrons, that’s helium, and you fill that rung, and helium is chemically inert because the rung is full. Now, if you want to go to the next element, lithium, you have to go to the next rung. Lithium is very active. The next rung’s got a different shape, it turns out you can fill that, and they’re eventually filled when you’ve got up to about ten altogether. And there, I think, you’re now at neon, if I’m keeping track of things, which again is inert. Every time a rung was filled, you got chemical inertness. Add one or remove one, you get chemical activity.

  The filling of the rungs was because of Pauli’s exclusion principle, that you cannot put an electron on a rung that is already full, you cannot put one in a state that is already occupied. This principle, he added, forces the electrons to go into different places in the jigsaw and build up structures. From this, you get atoms and chemistry, you get solids, you get crystals. The significance is vast.

  Michela Massimi told how the news of Pauli’s idea spread very quickly. He called it a rule that could account for a series of anomalies when looking at spectra and problems with the periodic table. As far as she knew, the first person to call it a principle was Paul Dirac (1902–84) in 1926.

  MICHELA MASSIMI: Pauli announced it in a letter to Alfred Landé who was a prominent experimental physicist at Tubingen at the end of 1924. The news spread. A month later, Niels Bohr sent a letter from Copenhagen to Pauli saying, ‘We’re all very excited for the very many beautiful things you have discovered, and I don’t have to hide any criticism because you, yourself, Pauli, have described the whole thing as sheer madness.’

  People really were scratching their heads about the exclusion rule and what it meant, we heard. But Pauli’s insight was visionary. People who came after him introduced the term of electro-spin. A young PhD student from Columbia called Ralph Kronig said that maybe we can interpret the two-valuedness by thinking of the electron as a spinning top that can be spun clockwise or anti-clockwise, and that gives you the two values, plus one half and minus one half. Pauli, we heard, dismissed that idea as witty nonsense but, soon afterwards, two Dutch-American physicists, George Uhlenbeck and Samuel Goudsmit, published a paper introducing the idea of the electro-spin.

  Graham Farmelo picked up on Michela Massimi’s mention of Kronig who, he said, could have had a Nobel Prize-winning discovery, but Pauli broke him with his criticism. With his personality as it was, he could take ideas and crush them in people’s arms. One of his ex-wives later said he used to walk around their apartment polishing his barbs to make them as funny and poisonous as possible.

  GRAHAM FARMELO: There’s another physicist called Paul Ehrenfest, who walked up to Pauli. Allegedly, their first words were, he said to Pauli, ‘I like your physics better than I like you.’ And Pauli said, ‘Well, for me, it’s the other way around.’

  In that case, though, Pauli and Ehrenfest became firm friends. Pauli also, to the surprise of some, became close to Carl Jung, the great psychoanalyst. For someone so rigorous and logical, Pauli was very interested in the paranormal. In 1927, soon after his mother had killed herself, his father married a woman Pauli’s age and Pauli had his ill-fated marriage with a cabaret dancer, toured America and, drunk, broke his arm. His father steered him towards Jung. And then, Graham Farmelo said, they formed an improbable friendship. Pauli had become interested in psychology, partly from his closeness to Niels Bohr, who had very wide interests, and he agreed to have his dreams analysed, probably by one of Jung’s students.

  Albert Einstein with Wolfgang Pauli.

  MELVYN BRAGG: Frank, are these two things irreconcilable or is it just the way a man lives his life?

  FRANK CLOSE: I’m just making this up as I go along, but Jung, with his idea of the collective unconscious, the feeling that there is something going on beyond that that we are immediately aware of, is not radically different from Pauli, who is here at the birth of quantum mechanics and, fifty, sixty years later, we still use quantum mechanics without being quite comfortable as to what’s going on.

  Pauli’s second pièce de résistance, as Graham Farmelo described it, was his idea that predicted the neutrino. The nuclei of atoms can, in some cases, decay randomly and this is what we call radioactive decay, and there are different types. In one particular type of decay, a very high-energy electron comes out of the atomic nucleu
s unpredictably. From measurements, it appeared that the total energy before the process was not the same as it was afterwards. Some energy appeared to go missing. Niels Bohr thought that this may mean that energy conservation, which was a really sacred principle, might even be wrong. What was more, the electron came out with a range of energies, not one, which was odd. Pauli took his time and thought all this through, and came up with a third particle to go with the proton and electron.

  GRAHAM FARMELO: He wrote to a conference of physicists suggesting, very tentatively, that what was going on was that, in addition to the electron charging out of the nucleus, there was a particle that we don’t see. Now this particle, he deduced, very cleverly, from looking at the data, would have no electrical charge. It would have the same spin as the electron and very, very little mass. So he suggested this particle – it was later called the neutrino.

  He and many others at the time thought this particle would be undetectable. (Speaking after the programme, Graham Farmelo told how Pauli learned of the discovery of the neutrino while he was at CERN and read it out to a seminar, which must have been a wonderful moment. Frank Close added that Pauli handed over a case of champagne, which he had promised to do years before, on its discovery.)

  For all the importance of his ideas, it took twenty years for Pauli to be awarded a Nobel Prize and, in 1934, it was not as though he was edged out by a rival. In that year, no prize was awarded for physics as it was thought there was no one good enough. The view of the committee apparently was that ‘Pauli’s receptivity exceeds his originality’. He won it, though, in 1945 for his exclusion principle.

  MICHELA MASSIMI: The great legacy of Pauli is his visionary ability of realising the limits of classical physics in dealing with quantum entities. He was one of the few people at the time really working, still, within the old quantum theory that realised the limits of applying classical models to describing quantum entities. [He] remains one of the unfairly overlooked figures of quantum mechanics.