I have been thinking about this by Łukasz Rachel and Lawrence H. Summers this week: On Falling Neutral Real Rates, Fiscal Policy, and the Risk of Secular Stagnation.
It says an awful lot of true things. The average "neutral" 10-year safe real interest rate consistent with full employment in the Global North does look like it has fallen from 4% per year in the 1990s to -0.5% per year today. That does pose a huge problem for central banks that seek to use monetary policy s as the principal depression-fighting tool: a small negative shock that reduces this rate by only a little bit more would drive an economy into territory where the central bank cannot do its job. During this period of decline, increased government debts have put perhaps 2%-points of upward pressure on the neutral rate: the actual decline has been 6.5%-points.
But I find myself uncertain on what conclusions to draw from their paper. They focus on only one of what I think are three key interest-profit-discount rates in play here:
There is the (short or long) real safe interest rate on the securities of governments that issue reserve currencies and thus possess exorbitant privilege. This is down to today's -0.5% from 3% 20 years ago and 4.5% 40 years ago.
There is the long-term real risky discount rate at which the cash flows accruing to owners of capital are discounted in the market—the expected return on financial investments in stocks. This is at to 5% today, up from 4% 20 years ago, down from 12% 40 years ago, and down from 6% 50 years ago.
There is the societal profit rate earned by new investments in physical or intellectual capital. This is ??? to today's ???, from ??? 20 years ago and from ??? 40 years ago.
This third social profit rate is in some sense the fundamental opportunity-benefit-of-investment ground out by the real economy of production and distribution on top of which the financial superstructure is built.
The second is the quotient of profit flows over the market value stock, and takes the societal profit rate returns to society's capital and adds to them the amount of monopoly rents captured by enterprises, subtracts from them labor rents and spillover benefits, both organizational and technological, that are not captured by those who undertake the actions that generate those spillovers, and then values those cash flows at the long-term risky discount rate.
The first of safe interest rate is the second minus the liquidity and safety terms that lower the required rate of return on safe assets.
Łukasz Rachel and Lawrence H. Summers focus on rate (1): the (short or long) real interest rate on the safe securities of governments that issue reserve currencies and thus possess exorbitant privilege. The problem is that the wedge between this (1) safe interest rate and the risky discount rate (2)—the rate at which risky cash flows are discounted—is worse than poorly understood by economists: it is not understood at all.