convergence

If poorer countries can simply copy the technologies, machines and methods that rich countries spent generations inventing, they ought to be able to grow faster and gradually catch up. This intuitive idea, that gaps between rich and poor economies should shrink over time, is the convergence hypothesis, sometimes called the catch-up effect. It is one of the most tested and most debated predictions in the study of economic growth.

The logic comes straight from diminishing returns to capital in the Solow model. A country starting with very little capital per worker earns a high return on each new machine, so investment goes a long way and growth is fast. A country already rich in capital earns less from each additional machine, so it grows more slowly. Add the ability of latecomers to borrow proven technology rather than invent it, and the prediction is that the poor should grow faster than the rich and close the gap. The crucial refinement is conditional convergence: countries converge only toward their own steady state, set by their own saving rates, education, and institutions. So two countries converge to similar incomes only if they are similar underneath; a poor country with weak institutions may not catch up at all.

Convergence matters because it speaks directly to whether the world is becoming more equal. The evidence is mixed and humbling. Among countries that are already broadly similar, such as the regions of a developed nation or the members of a rich-country club, convergence shows up clearly. But across the whole world it is weak: some poor countries, like several in East Asia, have caught up dramatically, while others have stagnated or fallen further behind, caught in what is sometimes called a poverty trap. The honest conclusion is that catching up is possible but not automatic; it depends heavily on policy and institutions, not on poverty alone.