Technological advance, an engine of growth in the 1990s, also seems to have faltered. Economist Robert Gordon of Northwestern University argues that the information technology boom is weakening. A new study from the Federal Reserve provides some corroborating evidence. It finds that from 1995 to 2004, labor productivity — a measure of efficiency — in the nonfarm business sector increased 3.1 percent a year, with about half the gain coming from IT. From 2004 to 2012, average annual gains dropped to 1.6 percent, with IT providing slightly more than a third.

Finally, demographics may hurt. As Americans age, they may restrain their spending. (In 2000, the 65-and-over population was 12 percent of the total; by 2025, it is projected to be nearly 19 percent.) Their wants may not have decreased, but they don’t know whether they will outlive their savings. The decline in IRA and 401(k) retirement accounts — in many cases now reversed — could be repeated. Social Security and Medicare benefits could be cut. These uncertainties breed caution.

Cheap credit addresses none of these problems directly and, indirectly, does so only weakly. It can’t erase the memories of the financial crisis. It can’t create new technologies. It can’t make older people younger. At best, cheap money aided the housing recovery; at worst, it became a stock-market narcotic that can’t be withdrawn painlessly. Many countries face obstacles to growth that cheap money won’t magically remove.