Bruce Cleaver asks:
Pondering your thesis in TGS, (which has some evidence to back it up; the change in society from the early part of the 1900's to 1973 does seem sharper than subsequent change, irrespective of the status of median income), I would ask you (in all seriousness) what changes/inventions now, today, if they were to exist, would cause you to say "The change from 1973 onward was just as sharp". Flying cars? Affordable interplanetary space travel? Teleportation?
Teleportation is not required, though it would…suffice. Alleviating traffic congestion would have been a significant advance, though we are moving in the opposite direction. Add in a cure for cancer, 3-D printing, seventy percent green energy, life expectancy of ninety-five, a Segway that people want to use, and higher graduation rates than we had in the late 1960s, and we are getting there. Median family income of $90,000. As it stands, it seems we will be getting 3-D printing, although I am not sure exactly when or for how many items.
Coming at this from another direction, a few years in the late 1990s genuinely did not exhibit "great stagnation" numbers and this is consistent with on-the-ground observations at the time. Think of the last forty years, and imagine that thirty or thirty-five of them were like that period.