Other physical angles:

If the economy continues to grow at roughly the present rate, using more energy as it does so, when will we be consuming the entire solar energy output each year? And if this energy growth happens on the surface of the earth and heat dissipation works in a naive way then how long till the surface of the earth is as hot as the sun? Answers: A bit less than 1400 years from now to be eating the sun, and a bit less than 1000 years from now till Earth's surface is equally hot, respectively. Blog post citation!

The same blogger did a followup post on the possibility of economic growth that "virtualizes our values" (my terminology, not the blogger's, he calls it "decoupling") so that humanity gets gazillions of dollars worth of something while energy use is fixed by fiat in the model. Necessarily the "fluffy stuff" (his term) somehow takes over the economy such that things like food are negligible to economic activity. With 5% "total economy" growth and up-to-an-asymptote energy growth, by 2080 98% percent of the value of the economy is made of of "fluffy stuff" which seems to imply that real world food and real world gasoline would be less than 2% of the economy... which implies that the average paycheck would be spent on very very little food or gas and quite a lot on "fluffy stuff".

The blogger takes this as evidence that the fluffy economy is impossible and (implicitly) that we should just accept that civilization has peaked and should turn into lowered-expectations-hippies, but to me his "ridiculous" energy scenario sounds suspiciously similar to Hanson's em scenario. What use has an em for a real hamburger made out of real beef grown with real grass shined on by real sunshine? Very little use. It would be like having the deed to an extrasolar planet. How awesome would it be to be an em? Very much awesome :-)