@FreeNortherner The vast majority of economic value is produced from energy - coal, oil, natural gas, geothermal, animal power, etc.
The amount of "economic value" produced just with labor - human energy - is almost trivial. We're talking stone age.
@AJiazhang Yep, the One Weird Trick to power the economy has never materialized. New energy sources just augment the existing mix, we never use less.
As for electric cars, etc. - that's been a hope for over 100 years now.
@ded_ruckus Huge amounts of GDP are really just costs - healthcare spending, for example. It's no surprise that major hospitals are in large urban areas.
@OGRolandRat It's actually very common in the decline phase of an empire - see John Glubbs "The Fate of Empires" for example.
Sex and Culture by JD Unwin is another good reference.