The end of the golden age cannot be explained by some technological reversal. From iPad apps to shale gas, technology continues to advance. The underlying reason for the stagnation is that a half-century of remarkable one-off developments in the industrialized world will not be repeated.

First was the unleashing of global trade, after a period of protectionism and isolationism between the world wars, enabling manufacturing to take off across Western Europe, North America and East Asia. A boom that great is unlikely to be repeated in advanced economies.

Second, financial innovations that first appeared in the 1920s, notably consumer credit, spread in the postwar decades. Post-crisis, the pace of such borrowing is muted, and likely to stay that way.

Third, social safety nets became widespread, reducing the need for households to save for unforeseen emergencies. Those nets are fraying now, meaning that consumers will have to save more for ever longer periods of retirement.

Fourth, reduced discrimination flooded the labor market with the pent-up human capital of women. Women now make up a majority of the American labor force; that proportion can rise only a little bit more, if at all.