> This is a common argument, and you are quite right that people have been wrong about specific limits in the past, but to take that on to claim that there will be no physical limits ever seems to me to be pretty obviously wrong. You can't increase both population and consumption in a space of a defined size forever. Something has to give.
Well, at some point there will be so many people that nobody has room to move around and reproduce. I'm with the optimists here that we won't hit any "real" limits before this one -- roughly 1/3 of the earth's surface is solid land, while all of the earth's -volume- contains natural resources (the usual suspects, plus nuclear isotopes, plus geothermal energy, plus biomass...), and there is also ~1kW/m^2 of sunlight hitting half the planet at all times.
We don't even know what's at the bottom of the oceans, or what exactly is below the earth's crust.
And there are tons more resources in other parts of the solar system.