By now you've heard of the modern marvel that is the Tata Nano, best known as the world's cheapest car. Perhaps you also know that Tata, long one of India's industrial giants and an increasingly powerful global player, is facing dire straits. Tata's acquisition of the Britain-based luxury automaker Jaguar Land Rover (JLR) came at a particularly inconvenient time, shall we say, and its domestic market is reeling as well. So why should Americans care?

In 2005, Wharton finance professor Jeremy Siegel published The Future for Investors, a marvelous little book that, in my view at least, holds up relatively well. Siegel's read of the future is dominated by reading the demographic tea-leaves. The aging of the world's affluent societies poses a straightforward problem, summarized in this short summary of Siegel's book.

Many experts worry, for example, that there will not be enough younger Americans to soak up all the securities that baby boomers will want to sell to fund their retirements, with the excess supply driving down share prices and returns. Indeed, most of the industrialized nations will have aging populations, largely because of low fertility rates and longer life expectancies. In 1950, there were seven American workers for every retiree 65 or older. Today there are 4.9, and in 2050 there will be just 2.6. In Japan, there were 10 workers per retiree in 1950; there are 3.1 today and will be 1.3 in 2050.

After dismissing the prospect of a massive productivity boom as pie-in-the-sky -- let's not dismiss the power of superintelligent machines, Professor Siegel -- Siegel looks to emerging economies to save the day.

Economic advances in countries like China and India will give enormous buying power to their people, whose average age will be lower than in the developed nations. The developing nations will supply the goods that retired Americans will need, and they will buy the securities baby boomers will want to sell, creating enough demand to shore up equity prices, Siegel said, adding that the Chinese economy will be twice the size of America's by mid-century if China's per-capita income rises to half of America's. That's not an unlikely feat: In the past half-century, Japan, Hong Kong, Singapore and a number of other countries have achieved growth rates higher than that. "The future of the world economy is bright," Siegel writes.

This is small consolation at the moment, when China and India are nowhere near rich enough to come to rescue. But by the time I turn 135, I fully expect affluent young Asians to pay me handsomely for my meager assets. That is the entirely selfish reason why I am an enthusiastic free trader.