If it turns out the US Federal Reserve has inflated an asset price bubble in recent years then we can breathe a sigh of relief. It would be a hideously embarrassing mistake for the Fed and other central banks, of course, but it would suggest that more dismal fears, including those that go under the label of “secular stagnation”, are wrong as well.

Those who think there is a bubble believe that central banks have kept interest rates unjustifiably low. By buying bonds in the name of quantitative easing, they have created a false boom in asset prices. Rising inflation will soon expose this miscalculation, and rates will rise.

But that is actually the cheery scenario. It suggests that generating enough demand to keep economic resources fully employed will not be as hard as central banks expect – and thus they have already gone a bit too far with their stimulus.