A number of considerations make me doubt the US economy’s capacity to absorb significant increases in real rates over the next few years. First, they were trending down for 20 years before the crisis started and have continued that path since. Second, there is at least a significant risk that as the rest of the world struggles there will be substantial inflows of capital into the US leading to downward pressure on rates and upward pressure on the dollar, which in turn reduces demand for traded goods.
Third, the increases in demand achieved through low rates in recent years have come from pulling demand forward, resulting in lower levels of demand for the future. For example, lower rates have accelerated purchases of cars and other consumer durables and created apparent increases in wealth as asset prices inflate. In a sense, monetary easing has a narcotic aspect. To maintain a given level of stimulus requires continuing cuts in rates.
Fourth, profits are starting to turn down and regulatory pressure is inhibiting lending to small and medium sized businesses. Fifth, inflation mismeasurement may be growing as the share in the economy of items such as heathcare, where quality is hard to adjust for, grows. If so, apparent neutral real interest rates will decline even if there is no change in properly measured rates.
I already had read the FT piece, but Neil Irwin on Twitter directed my attention to the importance of those paragraphs in particular. I do not always agree with Summers, but pondering his conundrums is never a mistake.