[hyperpape]

I think you're getting this backwards--this is not an argument that there's more limits, it's an argument over whether limited energy actually implies limits to growth. What the economist says is "even if energy is limited, growth is not" and the physicist goes on to rebut that claim.

[uxcn]

The rebuttal has to do with the definition of economic growth (assuming it isn't connected to energy consumption and gdp), which the economist argues has to do with quality of life. The rebuttal is that quality of life can only objectively improve to a certain point, and that the remaining measures aren't really quantifiable.

So the last, albeit minor, argument is that there would be a point where there isn't anything to invest in to grow, which essentially describes the ultimate form of secular stagnation. I think the economic counter-argument goes something like the money supply isn't inherently finite. I could see that being an interesting argument.