The role of physical constraints on production
通过引入质量函数连接物理产出与质量，发现资源投入的边际产品存在上限，挑战了传统Inada条件，对长期增长和环境可持续性有重要影响。
We consider the physical constraints of the production process by connecting the actual amount (volume) of physical output to its mass. To achieve this, we introduce a function that evaluates the mass of physical objects such as resources and output. Through the mass function, we demonstrate that the marginal product of resource inputs is less than the ratio of the mass density of resource inputs to that of the final products. This ratio's boundedness implies that the marginal resource product has an upper limit, meaning that the Inada condition for resources is not valid. This restriction on the marginal product of resource input has significant implications for long-term growth and environmental sustainability. It indicates that the growth of total physical output is only feasible with more resource input and a potentially higher level of pollution.