Networks are expanding up, down, in, out.

Byline: Tom Siegfried

A generation ago, "network" meant NBC, ABC or CBS.

Adding CNN and FOX to the list didn't change the basic idea. But as computers began to compete with televisions for eye time, networks spread from the airwaves to cyberspace. Today the

network is the Internet _ joined by its famous offspring, the World Wide Web. And that switch of cultural focus from TV to computers has inspired an even broader notion of what networks are and an explosion of interest in how they work.

Nowadays, networks are everywhere, and everything is a network. Networks permeate government, the environment and the economy. Food chains have become food webs. Brains are networks of cells. Networks are us.

Society depends on energy networks, communication networks and transportation networks. Bodies contain networks of organs, blood vessels, muscles and nerves. Atlases depict networks of rivers and roads. The business world is a network of buyers and sellers, including, it would seem, networks of insider traders. In any event, everybody knows about networks of good ol' boys _ in politics, industry, and even academia.

But diverse as they are, networks share common features. And scientists have now begun to figure out how to describe those features in a mathematically precise way. As a result, the science of networks has migrated from mathematical obscurity to radio talk shows. TV commercials starring Kevin Bacon exploit how well networked he is. And physicists have infiltrated the roster of experts studying computer systems, international trade, protein chemistry, airline routes and the spread of disease.