@VulgarKitten said:
Population growth isn't a cure-all, but in the present economic situation it's likely to make the resolution of a range of problems much easier.
For Japan, maybe. For the United States, I doubt it. Last time I checked, the majority of theorists believe that there will be a huge economic problem in the near future as the baby-boomers become decrepit, productivity per capita drops, and we suffer another recession.
However, here's where I (and my research) differ from the converse school of thought: Kremer and other more recent theorists (Galor and Weil, Sorel) have stated and empirically confirmed that larger population is associated with higher population growth rates and faster technological development. Technological development, then, becomes a consequence of population growth, leads to an increase in labor productivity, per capita income and improvements in living conditions, and increased capitalism.
I can concede that larger populations will, by and large, have higher population growth rates and enjoy greater technological development, but I'm not willing to concede a reversal of causation, as suggested by your second comment.
Regarding Galor and Weil, this this paper by Lagerlof confirms my original criticism. In it, the author hypothesized:
"We also show that these cycles are not an artifact of the two-period life setting: allowing adults to live on after the second period of life with some probability does not make the oscillations go away. Rather, the cycles are driven by fertility being proportional to per capita income minus the parental subsistence requirement. When population is large, and per-capita incomes close to subsistence, fertility is therefore sensitive to changes in population levels."
This suggests that fertility -- or population growth -- is sensitive to the difference between per-capita income and subsistence income. Further, per-capital income flatten to subsistence as overall production reaches its demand-based limit. So, I'm not seeing population growth as a good thing at all, or that the relationships are more than observational.
That said, I don't intuitively see where population growth any causal connection to technological growth. My understanding is that technological growth is tied directly to investment into education and research. Larger populations tend to have the public income necessary to fund technological growth, but I don't think the population factor has a direct relation.
As for Japan, its country faces somewhat unique circumstances. It's difficult to suggest that any "traditional" or "general" fix would apply to it.