The sun generates nearly 400 trillion trillion watts per second but don't let that fool you into thinking there's such a thing as a free lunch for more than a few billion years.
Sure, the amount of that work is going down, and has been going down for centuries, but that's not an inevitable, natural process: The technological innovation to make food easier and cheaper to produce also requires work.
1. stuff people would do for free, for patriotism, for fun, or for kudos
2. stuff it takes economic coercion to make people do
I can't offhand think of any #2 that couldn't in principle either be automated away, or harmlessly abandoned.