Questions over the colossal investment by US tech companies in artificial intelligence, now running at $400bn a year, continue to come thick and fast.

Will it, sceptics ask, ever be recouped, let alone generate the magical returns AI zealots expect? Leaders of the financial world from Kristalina Georgieva, IMF managing director, to Jamie Dimon of JPMorgan Chase have warned of an abrupt market correction. Could this be one of history’s more extreme cases of irrational exuberance?

That phrase, you may recall, was coined by Fed chair Alan Greenspan at the start of the dotcom bubble. He later backtracked, declaring that bubbles could only be detected after the event. The revisionist Greenspan view overlooked that in any bubble there are always shrewd people who see what is coming. For example, on the eve of the 1929 Wall Street crash statistician Roger Babson warned that a “terrific” crash was imminent. More recently Jeremy Grantham, co-founder of US fund manager GMO, famously predicted the bursting of the great Japanese bubble, the dotcom bust and the 2007-08 financial crisis. In the UK fund manager and philanthropist Jonathan Ruffer earned strong returns for his clients around the dotcom blow-up, the great financial crisis and the Covid market plunge. Yet such contrarian voices are always drowned out by those who claim that “this time is different”.