[nayaketo]

Theoretically, if immigration wasn't an option, what would happen in this case? Just imagine entire earth is well developed, so this issue is present on every single nation on earth. What would happen then? Would economy just slow down or would everything come crashing down? Would automation see widespread adoption? Anything else?

[mytailorisrich]

Economic growth would slow down because it would be based purely on productivity gains rather than productivity gains and producers/consumers base growth (and automation would likely have a big part to play in that).

But that would not necessarily be a bad thing as that would force to indeed focus on productivity growth and growth of indicators per capita instead of overall indicators.