THE English have Silicon Fen and Silicon Roundabout, the Scots have Silicon Glen. Berlin boasts Silicon Allee, New York Silicon Alley. But the brain of the tech world is the ecosystem in and around San Francisco. Silicon Valley’s entrepreneurs and innovators, technologists and moneymen are busy revolutionising nearly every aspect of the global economy.

A place named for its skill in making silicon-packed semiconductors is transforming how firms make decisions, people make friends and protesters make a fuss. Startups touch more people, more quickly than ever before. Airbnb, a seven-year-old firm that helps people turn their homes into hotels, operates in 34,000 towns and cities around the world. “On-demand” firms like Uber are changing what it means to be an employee. Just as the big platforms like Google, Facebook and Apple benefit from “network effects”, because each new user makes the service more valuable for all the others, so the Valley’s success as a venue to launch, fund, staff and sell a technology firm is feeding on itself (see article).

As a result, American capitalism has a new hub in the west. Wall Street used to be the place to seek fortunes and make deals; now it is increasingly the Valley. The area’s tech companies are worth over $3 trillion. Last year one in five American business-school graduates piled into tech. Jamie Dimon, the boss of JPMorgan Chase, has warned of mounting competition for Wall Street. Goldman Sachs recently held its annual shareholder meeting in San Francisco.

The enormous, disruptive creativity of Silicon Valley is unlike anything since the genius of the great 19th-century inventors. Its triumph is to be celebrated. But the accumulation of so much wealth so fast comes with risks. The 1990s saw a financial bubble that ended in a spectacular bust. This time the danger is insularity. The geeks live in a bubble that seals off their empire from the world they are doing so much to change.

Silicon lining

The American economy would be hit hard by a repeat of the financial shock that followed the dotcom crash in 2000. With the NASDAQ index near its record high, this is a common fear. Fortunately, although money and talent are pouring into the Valley, there is not yet much danger of a disastrous bust. That is because tech companies today not only have more robust business models than their dotcom predecessors did (ie, many actually make money), but they also rely on a smaller group of financial backers.

Today’s firms are staying private for longer. Tech firms that went public in 2014 were on average 11 years old; back in 1999 they waited only four years before listing their shares. Tapping wealthy investors means risk is borne by people who can afford to take losses. It is easy to lament the decline of the publicly listed company (though even when founders do list they keep a tight rein), but if tech firms fall short of their promises, ordinary investors are less likely to see their wealth destroyed.