The returns on trillions of dollars of spending are deeply uncertainYOU AIN’T seen nothing yet. Last year America’s biggest technology companies, including Amazon, Google and Microsoft, spent $450bn on infrastructure, much of it to power artificial intelligence. This was just an amuse-bouche. For the main course they will this year spend $900bn on chips, data centres, power and so forth, with a $1.4trn pudding to follow in 2027. To fund this feast they have borrowed more than $400bn this year. T...