**Must-Read:** The fact that Bloom et al. think that exponential growth is the baseline and the rule is rather odd, as is the use of the word "harder". We have had 25 Moore's Law cycles since the early 1970s. That means that computer chips now are 2^25 = 32,000,000 times as dense as they were then. And Bloom et al are surprised that it takes 25 times as many researchers to move computer chips from 32,000,000 to 64,000,000 times as dense as they were in 1970 as it took then to move to twice the 1970 density? It does seem to me that just because exponential growth models are easy to write down does not mean that they should always be our instinctive default...

**Nicholas Bloom et al.**: *Are Ideas Getting Harder to Find?*: "In many growth models... the long-run growth rate is the product of... the effective number of researchers and... research productivity...

...We present a wide range of evidence from various industries, products, and firms showing that research effort is rising substantially while research productivity is declining sharply. A good example is Moore’s Law. The number of researchers required today to achieve the famous doubling every two years of the density of computer chips is more than 25 times larger than the number required in the early 1970s. Across a broad range of cases and levels of disaggregation, we find that ideas--and in particular the exponential growth they imply--are getting harder and harder to find. Exponential growth results from the large increases in research effort that offset its declining productivity.