Slower growth in the working-age population also means less competition for jobs worldwide, which goes a long way to explaining why unemployment is now at record lows not only in the United States but also in Germany and Japan. Surely that’s not a bad thing.

Whatever politicians tell the public, their attempts to bring back the miracle years are ill advised. Growth in the economy is driven by growth in the number of workers and in output per worker, or productivity. But since the postwar surges of 1950s and 60s, productivity growth has slowed, also defying government efforts to lift it.

For a time, the global economy kept motoring along anyway, fueled by a surge in debt. In the 1980s, central banks began winning the war on inflation, which allowed them to drop interest rates sharply. Lower borrowing costs unleashed a worldwide binge that saw debt surging from 100 percent of global gross domestic product in the late 1980s to 300 percent by 2008.

Then the global financial crisis hit, ruining many private borrowers and lenders, many of whom are still wary of taking on new debt. After growing faster than the economy for three decades, debt growth in many countries, including the United States, has fallen back in line with economic growth. Even China, the one major country that dodged the crisis and experienced a surge in lending after 2008, is now reluctant to build on the mountain of debt that already weighs down its economy.

So the postwar miracle is over. Economic growth is weighed down by the baby bust and the debt hangover. Yet because economists continue to base forecasts on miracle rates of growth — 4 percent for the world, 3 percent for the United States — policymakers keep fighting to hit these targets. This is very risky.

There are growing calls from economists on both the right and the left to lower interest rates, or increase government spending, to boost growth even if that risks higher inflation. At the Federal Reserve, too, there is an emerging view that letting inflation rise above 2 percent, long considered a red line, may not be unwise.

The underlying assumption seems to be that policymakers must take action because 2 percent G.D.P. growth is intolerably slow. But must they? The confidence surveys suggest Americans are quite content with record-low unemployment, benign inflation and 1.4 percent growth in gross domestic product per capita. Why then the rush to pump more money into the economy, which risks rekindling its debt problems and inflation?