Do you agree that that is a pretty hard limit?

PS: 1% growth per year seems slow and sustainable but in 20,000 years your talking about 2.7 with 86 zeros after it. Start with 1 atom for one second and compare it with every atom in the earth for a year and your only at 4.2 with 57 zeros. So if the total economic output of humanity was 1 atom we could not sustain 1% economic growth per year for 30,000 years.

Edit: This assumes that the economy is based on physical goods, if we assume intangibles can take up 99.99...9% of the economy then 1% growth is possible for long periods of time even if it's somewhat meaningless.

There are limits to what you can do with matter. It's unlikely the economy (our productive capacity) will continue to grow much for 100,000 years after all mass we can get at is weird ass artificial quark composite computronium.

However, energy needs do seem to increase with productivity, and there's limit on how much energy we can get from the sun (a dyson sphere encloses the sun, capturing all its energy). But there's some assumptions here: that we can't discover ways of being productive that require less energy (and wouldn't that enhancement itself be "productive"?); that we can't discover other sources of energy (e.g. room temperature fusion micro-suns - or something better).

Once you factor in the unknown (i.e. knowledge that we don't yet have) it's hard to know what the limits are. I guess the entire universe is a limit on matter... if we can't discover a way to make more matter... or more universes.