The danger, of course, is that if a hub fails, it could become a giant superspreader. ‘If there is a big shock, it makes things worse because the risk is concentrated,’ said Barbara Casu, an economist at Cass Business School.[97] ‘It should act as a risk buffer, but in extreme cases it could act as a risk amplifier.’ To guard against this problem, hubs have access to emergency capital from the members who use them. This mutual approach has drawn criticism from financiers who prefer an every-firm-for-themselves style of banking.[98] But by removing the tangle of hidden loops from the network, the hubs should mean fewer opportunities for contagion, and less uncertainty about who is at risk.
Despite progress in our understanding of financial contagion, there is still work to be done. ‘It’s like infectious disease modelling in the 1970s and 1980s,’ said Arinaminpathy. ‘There was a lot of great theory and the data had some catching up to do.’ One of the big obstacles is access to trading information. Banks are naturally protective of their business activities, making it difficult for researchers to form a picture of exactly how institutions are connected, particularly at the global level. This makes it difficult to assess potential contagion. Network scientists have found that, when examining the probability of a crisis, small errors in knowledge about the lending network could lead to big errors in estimates of system-wide risk.[99]
Yet it’s not only a matter of trading data. As well as studying the structure of networks, we need to think more about Newton’s ‘madness of people’. We need to consider how beliefs and behaviours arise, and how they can spread. This means thinking about people as well as pathogens. From innovations to infections, contagion is often a social process.
3
The measure of friendship
The terms of the wager were simple. If John Ellis lost at darts, he had to get the word ‘penguin’ into his next scientific paper. It was 1977, and Ellis and his colleagues were in a pub near the CERN particle physics laboratory, just outside Geneva. Ellis was playing against Melissa Franklin, a visiting student. She had to leave before the end of the game, but another researcher took her place and sealed the victory. ‘Nevertheless,’ Ellis later said,[1] ‘I felt obligated to carry out the conditions of the bet.’
That raised the question of how to sneak a penguin into a physics paper. At the time, Ellis was working on a manuscript that described how a particular type of subatomic particle – the so-called ‘bottom quark’ – behaved. As was common in physics, he sketched out a diagram with arrows and loops showing how the particles would transition from one state to another. First introduced by Richard Feynman in 1948, these ‘Feynman diagrams’ had become a popular tool for physicists. The drawings provided Ellis with the inspiration he needed. ‘One evening, after working at CERN, I stopped on my way back to my apartment to visit some friends living in Meyrin where I smoked some illegal substance,’ he recalled. ‘Later, when I got back to my apartment and continued working on our paper, I had a sudden flash that the famous diagrams look like penguins.’
Ellis’s idea would catch on. Since the paper was published, his ‘penguin diagrams’ have been cited thousands of times by other physicists. Even so, the penguins are nowhere near as widespread as the figures they are based on. Feynman diagrams would spread rapidly after their 1948 debut, transforming physics. One of the reasons the idea sparked was the Institute for Advanced Study in Princeton, New Jersey. Its director was J. Robert Oppenheimer, who’d previously led the US effort to develop the atomic bomb. Oppenheimer called the institute his ‘intellectual hotel’, bringing in a series of junior researchers on two-year positions.[2] Young minds arrived from around the world, with Oppenheimer wanting to encourage the global flow of ideas. ‘The best way to send information is to wrap it up in a person,’ as he put it.
The spread of scientific concepts would inspire some of the first research into the transmission of ideas. During the early 1960s, US mathematician William Goffman suggested that the transfer of information between scientists worked much like an epidemic.[3] Just as diseases like malaria spread from person to person via mosquitoes, scientific research often passed from scientist to scientist via academic papers. From Darwin’s theory of evolution to Newton’s laws of motion and Freud’s psychoanalytic movement, new concepts had spread to ‘susceptible’ scientists who came into contact with them.
Still, not everyone was susceptible to Feynman diagrams. One sceptic was Lev Landau at the Moscow Institute for Physical Problems. A highly respected physicist, Landau had clear ideas about how much he respected others; he was known to maintain a list rating his fellow researchers. Landau used an inverted scale from 0 to 5. A score of 0 indicated the greatest physicist – a position held only by Newton in the list – and 5 meant ‘mundane’. Landau rated himself a 2.5, upgrading this to a 2 after he won the 1962 Nobel Prize.[4]
Although Landau rated Feynman as a 1, he wasn’t impressed by the diagrams, seeing them as a distraction from more important problems. Landau hosted a popular weekly seminar at the Moscow Institute. Twice, speakers tried to present Feynman diagrams; both times they were kicked off the podium before they could finish their talks. When a PhD student said he was planning to follow Feynman’s lead, Landau accused him of ‘fashion chasing’. Landau did eventually use the diagrams in a 1954 paper, but he outsourced the tricky analysis to two of his students. ‘This is the first work where I could not carry out the calculations myself’, he admitted to a colleague.[5]
What effect did people like Landau have on the spread of Feynman diagrams? In 2005, physicist Luís Bettencourt, historian David Kaiser and their colleagues decided to find out.[6] Kaiser had previously collected
