It is pretty simple, really. The size of the economy, GDP and other metrics don't really matter. The real measure is how many hours does a person need to trade to get a particular product or service. If that goes to zero, we will be in good shape even if GDP is high or low. Nice to see that the "this-cant-go-on" author knows how to calculate 1.02^N and shocked themselves when typing a somewhat large N into the calculator. The thing they forgot is the size of the economy doesn't mean anything on its own. It isn't a physical thing that will take up all of the space in the universe eventually as the author seems to fear.