If that's an accurate quote, Herman Daly is spot on. However, you said "sustainability needs a time reference." Why? If you add any period at all, then you have a problem next year because your strategy now covers a smaller period (let's say 99 years instead of 100 years). The only sensible approach is to use a time reference of "indefinitely". That's a challenge, but any strategy for a finite period of time is not a strategy for sustainability.

I'm just glad we can leave the death of the Sun and Proton decay for future generations to worry about...

Nick.