Whatever the precise cause, the slowdown shows up in the data. Mark Zandi and colleagues at Moody’s Analytics concluded that aging over the past 15 years reduced productivity in the United States by 0.25 percent to 0.7 percent per year.

Other researchers suggest that an older, smaller labor force can also account for the sluggish rate of business start-ups. Roughly half of American companies are at least 11 years old, up from less than one-third in the late 1980s. For all the hype about Silicon Valley’s explosive entrepreneurship, there are fewer young companies entering the marketplace now than there were a generation ago. Hugo Hopenhayn of the University of California, Los Angeles, and colleagues argue that this is caused in large part by a declining labor supply.

As big, old companies come to dominate the marketplace, their increasing market power could mute their incentive to innovate. Mr. Hopenhayn and others have found that larger firms share less of their revenues with their workers, trimming workers’ share of national income.

The declining supply of workers may not even be the most intense headwind unleashed by our aging population. The most worrying feature of our time, instead, may be older workers’ high rate of savings and low rate of spending, as they build nest eggs to support themselves through what is likely to be a long retirement. Over the past 20 years or so, this thriftiness has helped pushed interest rates — the price of money — down to near zero , making it hard for the Federal Reserve to cut rates further to stimulate the economy when needed.

More immigration might help address some of the shortcomings of our aging labor force. Yet in the current political environment, the odds that the United States will open the door to more foreign workers look, to put it mildly, slim.

Tax breaks, child subsidies, paid leave and other regulations have had some modest success in increasing fertility rates in countries like France, Canada and Sweden. But there is scant evidence that policy could slow aging significantly by encouraging Americans to have more children.

One great paradox of this predicament is that robots could help address some of these problems, replacing workers that age out of their productive lives.