Economy
"But economics is not a zero sum game, the economy is not limited as to size in any fixed sense."
If we're talking fundamentals, the size of the world economy is the difference between all the stuff we've ever mined, harvested or extracted and all the stuff we've thrown away, burnt, lost, worn out, rusted, blown up or eaten. Even a good old fashioned honest hard day's work requires a food input (though some of us, me included, have a few of those stored up around our waistlines).
Everything else such as money (and printing more or less of it), growth, profit and loss are simply humanity's way of divvying that up among ourselves.
And forget environmentalism. Unnecessary consumption/disposal/wastage is simply a good way of making us all poorer. The trouble being that that is apparent only in macro economics. It's not something that many people think about when they're chucking something out.
So you're nearly right. The economy is limited by the resources available to us on this planet. One day, no matter how careful we are here with our resources on earth, we'll have to go off and mine some asteroids, etc.