Where I have landed on “ideas getting harder to find”, in a nutshell
Some very brief thoughts (for those who are familiar with these issues, sorry I am not including all the background/intro):
At the same time, we get better at finding them (more efficient and more total inputs)
Rates of growth have to be explained in terms of the balance of these factors, not one alone
Stagnation (i.e., slower growth) the last ~50 yrs is partially but not fully explained by this balance
Deceleration is a historical aberration; the long-term historical pattern is acceleration. This indicates that (2) generally outpaces (1) over the long term, and I see no reason for this to change in the foreseeable future
(If ideas getting harder to find were the only relevant factor, then progress would have been fastest in the hunter-gatherer era—so much low-hanging fruit! But again, the reality is the opposite trend.)
For a longer treatment of some of this, see this draft essay.