By the late 2000s, though, the volatility of the tech sector is indistinguishable from that of the overall index. Microsoft and Cisco, the disruptive entrants of the 1990s, now bear the risk profile of a Procter & Gamble.

The internet promised to open new horizons for the market entrant with an unusual idea. The most successful internet companies in today's America settle their users into familiar patterns of behaviour: Facebook, for example. Startups still proliferate, to be sure, but they accommodate themselves to the social-media giants like barnacles on a supertanker. There are many possible explanations for the dearth of disruptive innovation, from the technological to the demographic — ageing populations take fewer risks than younger ones — but the facts are indisputable.

Of all the world's economies, China has seen the most disruption in the past generation. But China is at a crossroads, Phelps cautions: "While the world sees world-class dynamism, the Chinese discuss how to acquire the dynamism for indigenous innovation, without which they will be hard pressed to continue their fast growth."

Between 1987 and 2013, household income in China rose 16-fold as the country's population migrated from low-productivity rural employment to industrial jobs in the cities. China could not perpetuate a growth model dependent on exports fed by cheap labour even if it wished to: its reserves of rural labour are shrinking and wages are converging on the low end of the industrial world.

China has to innovate. How likely is it to succeed? To Westerners, Chinese culture appears conformist rather than individualistic, prone to copy rather than invent. When Deng Xiaoping began his industrialisation drive in 1978 China was better served by acquiring Western technology than inventing its own.

As a proportion of GDP, China's R&D spending is now close to that of Western Europe, and the country has made impressive advances in dual-use technologies with military as well as civilian applications: computation, missiles, satellites, telecommunications and high-speed rail. If we follow Phelps's logic, though, science and engineering are not the springboard for mass flourishing. We have to look to the character of society itself. The Western consensus leans towards pessimism about China.

It is true that the China of the Cultural Revolution was the most all-encompassing totalitarian state of which we know, where independent thinking bore with it existential risk. Precisely because China is emerging from an era in which conformity was imposed in the most brutal fashion, into a period where entrepreneurship is not only tolerated but encouraged, the change in China's character is perhaps the most radical of any society in the world. The reforms undertaken by the new government of Xi Jinping may sink into a bog of cultural conformism. But they also might release the pent-up entrepreneurial energies of the most educated and confident generation in Chinese history. 

A dozen years ago Jack Ma, founder of Alibaba, a business-to-business trading platform, was teaching English at a government university. Entrepreneurs like Tencent's Ma Huateng and Huawei's Ren Zhengfei have created firms that are shaking the foundations of the Chinese economy, with the blessing of its government. Chinese universities may not produce as many prospective innovators as their Western counterparts, but Chinese firms are now hiring Western scientists and engineers by the thousand.