The paper "Recombinant Growth" by Martin L. Weitzman explores the microfoundations of the knowledge production function in an idea-based growth model. It introduces a production function for new knowledge that depends on the recombinant combinations of old ideas, drawing an analogy with agricultural research stations developing new plant varieties through cross-pollination. The core of the model is a theory of innovation based on the combinatoric feedback process, where new ideas emerge from the reconfiguration of existing ones. The paper argues that the ultimate limits to growth lie not in the ability to generate new ideas but in the ability to process a vast number of potentially new ideas into usable form. The analysis is supported by a mathematical framework that demonstrates how a binary recombinant expansion process can outperform exponential growth. The main result of the paper is a theorem that shows the long-run growth rate is a linearly homogeneous function of two savings rates, influenced by the aggregate production function and the ultimate-limiting cost of R&D. The paper discusses the implications of different values of the ultimate-limiting cost of R&D, including cases where it approaches infinity or zero, and concludes that the positive limiting case is the most plausible scenario.The paper "Recombinant Growth" by Martin L. Weitzman explores the microfoundations of the knowledge production function in an idea-based growth model. It introduces a production function for new knowledge that depends on the recombinant combinations of old ideas, drawing an analogy with agricultural research stations developing new plant varieties through cross-pollination. The core of the model is a theory of innovation based on the combinatoric feedback process, where new ideas emerge from the reconfiguration of existing ones. The paper argues that the ultimate limits to growth lie not in the ability to generate new ideas but in the ability to process a vast number of potentially new ideas into usable form. The analysis is supported by a mathematical framework that demonstrates how a binary recombinant expansion process can outperform exponential growth. The main result of the paper is a theorem that shows the long-run growth rate is a linearly homogeneous function of two savings rates, influenced by the aggregate production function and the ultimate-limiting cost of R&D. The paper discusses the implications of different values of the ultimate-limiting cost of R&D, including cases where it approaches infinity or zero, and concludes that the positive limiting case is the most plausible scenario.