THE global financial crisis was a scarring experience for rich economies. A sharp short-term decline in GDP has given way to steady erosion in growth relative to pre-crisis hopes. Yet as a chapter in the International Monetary Fund’s new World Economic Outlook explains, the emerging world is also entering an age of diminished expectations. The IMF reckons that potential output in advanced economies was already on the decline in the years before the crisis, thanks to weak productivity growth (as the IT-driven boom of the 1990s petered out) and ageing workers. Potential growth is an estimate of an economic speed limit—how rapidly an economy can grow before inflationary overheating sets in—determined by growth in the labour force, the capital stock and productivity. The crisis squeezed investment, amplifying underlying weakness. Potential growth, which averaged 2.2% from 2001-07 dipped to 2.0% on the eve of the crisis and to 1.5% in 2013-14 according to the Economist.