Net gain.

• Author: Thompson, Nicholas

ALBERT-LASZLO BARABASI HAS A theory that he thinks may explain the spread of cancer, the Asian economic meltdown, and the ubiquity of Washington insider Vernon Jordan. To understand it all, you have to follow a simple rule: "Think networks."

To illustrate his point, Barabasi uses the famous game, "Six Degrees of Kevin Bacon," in which the second-tier movie star can be linked with almost any other actor in a couple of simple steps. Charlie Chaplin, for example, was in A King in New York with Robert Arden, who was in Little Shop of Horrors with Steve Martin, who was in Novocaine with Bacon himself.

The implications of the Kevin Bacon game may seem a little ho-hum, but after Barabasi explains the early mathematical debates over networks, Linked gets really interesting, showing how this new science promises to change the way we conduct everything from medical treatment to the war on terrorism.

For years, researchers assumed that networks operated through what statisticians call "normal distributions," with an average, or mean, and a bell curve around that average. Human height, for instance, follows normal distribution, as most people are between five and six feet tall, with a few taller and a few shorter.

But now we know that networks are often organized in what statisticians call "power distributions," with most data points clustered together at a low level, with a few out on the extreme. If height followed a power distribution, most people would be very short, but numerous 100-foot-tall men and women would wander the streets, and at least one 8,000-foot-tall man would work somewhere as a window-washer.

The result of this distribution is that the hubs (the really tall people) play a dramatic role in linking things together. On the Web, for example, Barabasi has found that browsers can get from pretty much any page to any other through about 19 links. That number is so low because a few sites such as Yahoo! can lead almost anyplace, even though a vast majority of Web pages have three or fewer links connecting to them.

The same is true of human beings socially. Most people have a core group of friends, but a few extraordinary connectors know thousands of other people and can link them all together. Malcolm Gladwell illustrated this point in his famous New Yorker essay "Six Degrees of Lois Weisberg" Just as linkages between people in Chicago often pass through uber-socialite Lois Weisberg, Washington connections seem to flow through Vernon...