One of the simple lessons of the past year is that things can and do collapse. Tall buildings and big companies have their hidden weaknesses, and under certain stresses they are apt to crumble. It's troubling to ponder, but entire societies have their limits as well. Pushed beyond them, they will fall.

That warning sounds throughout The Hydrogen Economy (Tarcher/Putnam), a new book by cultural critic Jeremy Rifkin. Though Rifkin's vision of America's energy future is not ultimately pessimistic, it is full of sobering reminders of what could lie ahead. He offers hope that we might end up in a better, more democratic world where energy is cheap and clean, but there are no guarantees. In Rifkin's view, modern society is about to face the kind of crisis that defeated ancient Rome and other civilizations. To survive, we'll not only have to pit the best human impulses against the worst, but also go head to head with the deepest laws of nature.

Rifkin, president of the Foundation on Economic Trends in Washington, D.C., is one of the leading big-picture thinkers of our day. He and his researchers have compiled a series of trenchant studies on biotechnology, the future of work, the corporate push to own the public commons, and other emerging issues. Rifkin has also helped to define a new niche for the public intellectual as a gatherer of our vast but fragmented reserves of knowledge. His writing focuses less on what he knows than on what the culture knows. At a time when so many people in key places find it hard to 'connect the dots,' Rifkin has turned this critical function into an art.

In The Hydrogen Economy, Rifkin ventures into the field of energetics-the study of energy's role in nature, including human life. We tend to think of society as being shaped by human ideas and personalities, which is partly true. But examined through a longer lens, our cities and cultures can also be seen as expressions of energy, blooming like thunderheads on a summer day, only to fade as they vent their stores of heat.

If every society is an engine built around what it burns, what happens when the fuel runs out? That's the dilemma we now face. Rifkin's basic assumption, shared by many experts, is that the oil age is coming to an end. Given the world's dependence on oil, we're doomed to global upheaval unless we switch to what he believes will be the fuel of the future.

Hydrogen is a colorless, odorless, flammable element that abounds throughout the universe, though it's usually locked in a chemical bond with other elements. Unlike oil, coal, and wood, hydrogen contains no carbon and releases only heat and water when it burns. (Its name in Greek means 'water maker.') Being a storable fuel, hydrogen could be the sort of all-purpose 'energy carrier' that a modern mobile society demands. Interest in it is fast approaching critical mass. Along with hydrogen fuel cells running homes and businesses, there's talk of hydrogen-powered vehicles hitting the market in a few years. With the Bush administration now backing a program to develop hydrogen cars-while conveniently dropping support for better gas mileage in regular cars-a hydrogen bubble on Wall Street might not be far behind.