The Solow model articulates that the stable state growth occurs owing to technological change or progress. The model can be applied to a cross-country context where there is a stable state difference in output per effective person due to technological difference.
In addition, under general conditions technological differences are consistent with stable state income differences. The empirical specification, which is closer to the Solow model, explains that international differences in output per person are explainable by international differences in technology. It appears to provide a meaningful restriction for observed studies of international trade.