Everyone knows the "Kevin Bacon" game, which relies on the theory that links a shoe salesman in Sparks, Nev., through a series of six or fewer relationships to, say, the president of the United States.

But now, a Columbia University professor is testing the idea that there are only "six degrees of separation" between any two people in the world. And he may discover just how big the world really is.

"Everybody sees six degrees of separation and thinks it's so cool, the world is such a small place," sociology professor Duncan Watts said. "Maybe it's not that small after all."

Watts was fascinated by the original "six degrees" study, published by Stanley Milgram in 1967. Milgram, a social psychologist at Yale University, discovered that when he instructed 100 people in Boston and 200 people in Nebraska to try to contact a Boston stockbroker who was a complete stranger, it only took an average of six steps to link the first person and the stockbroker through shared acquaintances.

That idea became popularized in the John Guare play Six Degrees of Separation, which was made into a Will Smith movie and then transmogrified into "Six Degrees of Kevin Bacon," the cocktail party game where people try to link the Footloose actor to other Hollywood stars by the co-stars they've shared screentime with.

Among many, it became a generally accepted truth that spoke to a larger "brotherhood of man" linking all of humanity. But there were limitations in the original study, Watts said.

"There's the fact that 100 of the people (in Milgram's study) in Omaha were blue-chip stockbrokers," he said. "In the '60s, if you owned stock, you had to have a stockbroker, meaning that the study only took place in the small world of stockbrokers.

"Really, what hasn't been tested is the universal version of the claim. Can we get this to work all around the world?" he asked.

That's where the Internet comes in. Since September, Watts has been using his Web site, smallworld.sociology.columbia.edu, as a base to recruit people he calls "targets" from around the world and is challenging anyone to see how many steps it takes to contact one of them.

By tracing the steps and methods each participant uses to get to a target, Watts hopes to prove or disprove the six-degrees theory, while learning about how humans relate to each other.

As for the criticism that Internet users are hardly a universal pool, Watts said the Web is less socially exclusive each day. By the time the study involves 100,000 people, it ought to reflect worldwide trends.

So far, about 5,000 or 6,000 people are searching for a handful of targets from New York to Russia to Malaysia.

None of the targets, he said, is Kevin Bacon.

"We haven't actually asked him," he said, laughing. "It's something we've thought about. People also suggest Usama bin Laden as a target."

One of the targets is Pavia Rosati, New York-based writer and editor-in-chief of the trend-tracking Web site www.dailycandy.com. Though several people have already contacted her in a few quick steps, she wouldn't be surprised or dismayed if "six degrees" turns out not to connect to reality.

"I've never really believed that a villager in China could get to me in six jumps," she said.

Taking the opposite view is fellow target Steven Strogatz, a professor of applied mathematics at Cornell University, who in only four days, found himself being contacted by 23-year-old software product manager Karl D'Adamo. D'Adamo found Strogatz through an old college friend, a graduate student at Cornell who recently took a class that Strogatz taught.

"As a mathematician, I know that it would be difficult to make a world that wasn't small unless it were contrived very carefully," Strogatz said. "People don't live in separate islands with no linkage."