“The tools available to science have been improving at a dazzling rate,” he told me. “I’m not sure how, but the world of technology in 30 to 40 years’ time will be vastly different than it is today.”

Nonetheless, Professor Gordon’s argument is not easy to dismiss. He does not forecast that technological progress will slow to a crawl. His argument, rather, is that the explosion of innovation and prosperity from 1920 through 1970 was a one-time phenomenon. From now on, progress will continue at the more gradual pace of both the last 40 years and the period before 1920.

“There is plenty of room in my forecast for evolutionary change,” he told me. “What is lacking is sharp, discrete change.”

He is not the only economist forecasting slower progress, now that the burst of productivity gains of the late 1990s and early 2000s has waned. “Growth in educational attainment, developed-economy R&D intensity and population are all likely to be slower in the future than in the past,” John G. Fernald of the Federal Reserve Bank of San Francisco and Charles I. Jones of Stanford wrote in a recent article.

Professor Gordon’s view of slowing technological opportunities meshes with other bits of evidence.

Ben S. Bernanke, the former chairman of the Federal Reserve who is now at the Brookings Institution, points out that long-term interest rates have been declining for a very long time. This is in response partly to the accumulation of savings in China and other developing economies, which have been buying Treasury bonds hand over fist. But it also suggests that investors, whether they realize it or not, may agree with Professor Gordon’s proposition.

“People who invest money in the markets are saying the rate of return on capital investments is lower than it was 15 or 30 years ago,” Mr. Bernanke said. “Gordon’s forecast is not without some market reality.”

Other strands of data point in this direction. Business dynamism, measured by the role of new companies in the economy, appears to be waning. The share of employment in companies less than five years old dropped from about 19 percent in 1982 to 11 percent in 2011.