Economic growth = Research productivity × Number of researchers
The aggregate evidence, then, may tell us nothing about research productivity at the micro level. Hence, the contribution of this paper: study the idea production function at the micro level to see directly what is happening to research productivity there.
What if there is sharply declining research productivity *within*each product line, but growth is sustained by the cre- ation of new product lines? First there was steam power, then electric power, then the internal combustion engine, then the semiconductor, then gene editing, and so on. Maybe there is limited opportunity within each area for productivity improve- ment and long-run growth occurs through the invention of entirely new areas.
a constant number of researchers can sustain exponential growth if the variety- discovery function exhibits constant research productivity::Wait wouldn’t that require researchers to create new disciplines at a constant rate?::