I should have stated the original statement more clearly. If the global economy was 100X the size per capita, and demand for food was 100X (implying there's 100X as many people), could we feed everybody? With an economy 10,000X as big, could we grow 100X as much food?

I say we could easily do so. But you need all three 100X's: miss one and it would be probably impossible, as you say.

Easy to say "the economy". But Iowa, for instance, is all planted up. Not going to find another 3 million acres to plant. Much less 100X that. No matter how many people you throw at the problem. It just doesn't scale.

And most any place else has less yield per acre. So now what? Its a big world but the low hanging fruit is already in use.

100X is a mighty stretch. Even Wallace and Borlaug would throw up their hands.

3 million acres? That's the 10 largest ranches in Texas. Cover them over with greenhouses rather than the prime farmland in Iowa. And Texas ranches are relatively productive compared to Montana or Alaska or the Sahara or ...

Nope. Its impossible. There is a finite amount of nutrients. Phosphorus turns out to be the limiting reagent. Then there are freshwater supplies, and other problems.

http://www.livescience.com/16493-people-planet-earth-support...

0.099% of the Earth's crust is phosphorus. If that's the limiting reagent, then that's very easy to fix with money.

Freshwater is synthesized from seawater now. If the GDP increases 10,000% it will be inexpensive.

you are right. TIL

http://blogs.ei.columbia.edu/2013/04/01/phosphorus-essential...