New or revived concepts such as degrowth and the knowledge economy represent a necessary criticism to the conventional view on economic growth, especially in regard to their environmental criticism. Both ideas are related as degrowth needs the application of knowledge in order to be operationalised and both share as a desirable outcome the reduction of working time. However, both concepts also bear common flaws in their criticism, due to the lack of attention in their analysis of the biophysical side of the economic process that has been analysed in approaches such as societal metabolism. The document discusses these weaknesses with the aim of stirring the much needed debate on the limits to growth.