(FORTUNE Magazine) – Have you noticed people getting by with less stuff than they used to? Acting less materialistic? Invoking that stern Yankee adage, "Use it up, wear it out, make it do, or do without"?

Me neither. But believe it or not--and it's hard to believe in this bull-market Babylon--we are, strictly speaking, less materialistic than we used to be. And I can prove it.

Recall Alan Greenspan's arresting statement that America's total economic output weighs about the same now as it did 50 or 100 years ago. His point was that this represents a steadily increasing stimulus to international trade, as shipping costs become a shrinking proportion of the value being shipped. But there's another implication that's at least as important.

The U.S. population in 1900 was 76 million, vs. 275 million today. In the past century our annual economic output per person, in constant dollars, has more than quintupled (to about $33,000). Now, it would be unsurprising to find that in becoming five times richer we were each, on average, turning out five times more physical stuff. It would be remarkable to learn that we had somehow contrived to become five times richer without any increase in per capita creation of physical things. But Greenspan's statistic is far more stunning: By holding the weight of our total output about steady, we have become five times richer while producing 72% less material stuff per person than we did a century ago.

How can this be? The answer goes beyond the economy's long shift from goods to services. Crank the numbers, and you find that even as manufactured goods account for a shrinking proportion of the total economy, their value has risen steadily. The explanation is that in the Infotech Age, manufactured goods increasingly are congealed brainpower. As the table shows, any alchemist still seeking the philosophers' stone should call off the search: Intel turns something baser than base metal--sand (which becomes silicon)--into something far more valuable than gold, Pentium III chips.

Of course, in a general way this is what successful manufacturers have always done: apply intellect in various forms to raw materials to create profitable products. What's new and striking, and what my somewhat fanciful table suggests, is how far the process has gone--how much value some companies are able to extract from ever less physical material. As a rule, those that do it best are the most valuable companies. For example, looking at the car and steel prices in the table, it isn't surprising to learn that DaimlerChrysler (maker of the Mercedes-Benz) is worth more than General Motors (the Chevrolet's maker) or that either one is worth far more than America's ten largest steel producers combined.

Note that the magic ingredient, brainpower, can work in many ways. Sometimes it takes the form of ultrahigh technology, as in the Pentium chip. Sometimes it's brand power, as in the Hermes scarf. Most often it's both, as in the Mercedes-Benz.

The large point to remember about the declining role of physical stuff in the value of manufactured products is that it's good news. As Greenspan pointed out, it fuels trade, which makes all trading partners more prosperous. It may also let firms respond more quickly to changing markets; just think what business would be like if every warehouse had to be five times bigger than it is. And by processing fewer physical resources per capita, we each put less pressure on the environment.

It's hard to believe while watching your neighbors build bigger houses, buy more cars, and unload more excess junk on eBay. But believe it: As an economy, we're getting richer and thinner. And it feels great.