I don't see what he means by improving the quality of life while the GDP remains constant. I admit that GDP has imperfections, such as only measuring goods and services that are sold, but ignoring that any improvement in the quality of life is an improvement in the GDP. If it makes your life better, it's worth more.

I figure that economic growth would continue forever, but at a decreasing rate. The long-term growth would be more logarithmic, if not asymptotic, than exponential. Also, I think it could last longer than that physicist seems to think. Even assuming we don't leave the solar system, there's no reason to keep it in its current state. If we can do better in a thousand years by disassembling the planets, then at some point it will be worth while to mine from them to build space-stations, in which case we will disassemble the planets.