Economists have always recognised that the long-run growth of productivity is, in the end, almost the only thing that matters for the living standards of the population as a whole. Recently, there have been significant downgrades to consensus estimates of productivity growth which, if maintained for long, would have enormous effects on the attainable level of gross domestic product per capita.

But the future impact of technology on long-run growth is one of the great unknowns — perhaps even the greatest — in economics.

An excellent example of this uncertainty occurred at the FT Business of Luxury Summit last week, in contributions from Johann Rupert and Martin Wolf. The former painted a picture of unprecedented technical advance, quoting examples from The Second Machine Age by Erik Brynjolfsson and Andrew McAfee. This book has captured the imagination by describing a future in which machine learning increases at exponential speed, rapidly replacing human skills in large parts of the economy. In a world of robot technology, driverless cars and delivery-by-drones, measured productivity growth would surely advance very quickly.