Here’s Wikipedia:
Powell noted that the natural rate of interest needed to be considered in relation to the “natural rate of unemployment” (which Powell noted is often referred to as “u-star”, written u*) and the inflation objective (“pi-star”, written Π*). Powell then went on to note that the conventional approach to economic policy making was that “policymakers should navigate by these stars”. However, he said, although navigating by the stars can sound straightforward, in practice “guiding policy by the stars … has been quite challenging of late because our best estimates of the location of the stars have been changing significantly”. Powell reviewed the history of attempts to estimate the location of the “stars” over a 40-year period 1960–2000 and noted that over time, there had been significant revisions of estimates of the positions of the stars.
We should not look for the (r and U) stars to guide us to a happier future, rather we should look for the (NGDP) futures to guide us to happier stars.
In other words, we don’t know the level of r*. We don’t know the level of U*. But we do know an appropriate level for expected NGDP growth.
Interest rates are not the issue. Right now, NGDP is growing too fast. Get NGDP expectations right, and r and U will move to their natural rates.