William Faris walks fast. Trying to keep up with the 6-foot-3 Fulbright mathematics professor from Tuscon, Arizona, you may find yourself wondering aloud whether he played basketball in college.


"I never took part in organized sports," Faris says, and continues trudging. "I was a math nerd."


Back then, in 1963, Faris was working on his doctorate, a foray into the mathematical side of quantum mechanics, at Princeton University. And as a wide-eyed student of 24, he got the chance to study his topic for a year at Moscow University.


"When I was here in the 1960s, the mathematical tradition in Russia was still very strong," said Faris, now 56. "Being a mathematician or physicist was like being a musician. It was considered something cultured and in the public eye."


Now Faris, who has been tackling mathematical problems related to physics for the past 35 years, has returned to Russia -- this time as a visiting professor at the College of Mathematics at the Independent University of Moscow.


He revels in the enthusiasm of his students. "Teaching here is more leisurely and more argumentative," Faris said of the introductory course in probability, which he delivers in Russian. "Things don't start on time, and go considerably longer than planned. When it's at its best, people stand up during lectures and make spontaneous comments. In the States, our time is so fragmented. Here, it's nothing to spend an evening talking about math."


But Faris also worries about the future of math in the climate of great change in the former Soviet Union.


"It's in a very precarious state," Faris said. "In general, support for science has declined. It's a bit of an afterthought. A lot of the more eminent mathematicians have gone abroad."


When Faris left Moscow after 1963, he promised himself that he would keep up with the politics, literature and people he had grown to love in what was then the Soviet Union. He said he regrets that he let that commitment lapse as he focused all his energy on his profession instead.


"Math is a tough business," said Faris, who has been a mathematics professor at the University of Arizona for more than 20 years. "People who say the life of a college professor is leisurely don't know. You're trying to keep up with all these bright guys all over the world, to figure out what they're doing and see if you can contribute something."


Drinking tea and eating flaky pastries in the apartment where he scribbles possible solutions to problems on endless supplies of scratch paper, Faris kicks into teaching mode. Listening to him speak of the subject that has consumed him for over half of his life is a bit like attending a revival.


"It's seductive," he says, his blue eyes lighting up as he delves into the topic of quantum mechanics. "It's incredible that such a weird set of equations can describe reality. You start seeing a pattern in something and think that, with a little more insight, you could figure it out. The next thing you know you've spent a month on it. But you have to keep going. There's this feeling that you could get ultimate truth. It's a little like religion."