Andrew Strominger ties up the universe with strings

By William J. Cromie

Gazette Staff

Andrew Strominger '77 has an unusual background for a professor of physics. He lived in a New Hampshire commune as a teenager, worked in fields and factories in China, and wrote for a Chinese language newspaper in Hong Kong. Lastly, he played a key role in developing an idea that ties all the matter and forces of the universe together in a single theory.

It wasn't easy getting to that last stage. When Strominger was a Harvard undergraduate, his elders warned him to stay away from theoretical physics.

"I told him it was too tough a field," said his father, Jack Strominger '46, Higgins Professor of Biochemistry. His undergraduate adviser discouraged him, as did his graduate adviser at M.I.T., where he earned a Ph.D. Theoretical physics is a difficult profession with few jobs, they cautioned.

But Strominger persisted. He immersed himself in the complexities of string theory, the notion that everything in the universe consists of unimaginably small, stringlike objects. By the way they coil, twist, vibrate, rotate, and combine strings can become any type of known particle or force -- the building blocks of atoms, forces that hold atoms together, units of light, or units of gravity.

In 1995, he and two colleagues showed how even the smallest of black holes could turn into strings.

Such microscopic black holes are the decayed remains of huge relatives, big and energetic enough to swallow stars by their gravity. If strings can account for small black holes, they also should shed light on the mysterious behavior of their gigantic parents. Sure enough, last year, Strominger, working with Harvard physicist Cumrun Vafa and others, demonstrated mathematically that this is possible.

The discovery made Strominger, then at the University of California, Santa Barbara, a scientific celebrity. Many universities let him know that he would be welcomed to their faculties. Strominger decided that he and his family could have the "richest life" if he chose Harvard. He was appointed professor of physics last year.

"For me, the biggest professional issues were the superb faculty and the quality of students here," Strominger said. "Other factors were the presence of my parents, a job for my wife, who is a pediatrician, and good schools for my four daughters."

His father, Jack Strominger, has four sons and has been a professor of biochemistry here since 1968. They make a rare combination of father and son who serve on the faculty at the same time.

"In the past two years, Harvard has been one of the leaders in the string theory revolution," noted Professor of Physics Cumrun Vafa. "Andy's presence will reinforce that position. He also has a reputation as an effective and enthusiastic teacher on both the undergraduate and graduate levels."

A Nicer Alternative

When Strominger became interested in strings, it was an academic backwater. After receiving his Ph.D. in 1982, he did postdoctoral work at the Institute for Advanced Study in Princeton.

At the time, the main thrust of research there involved so-called quantum field theory, the behavior of subatomic particles and the forces that hold all matter in the universe together. "But [the Institute] allowed a few people to do odd things, and I was one of those people," Strominger recalled.

By the time, he moved to the University of California, Santa Barbara, in 1986, things had changed. A major problem in theoretical physics became how to join quantum theory with Einstein's predictions about the character of gravity. The words and equations used to describe the behavior of one could not be used for the behavior of the other. They were like two separate worlds. Physicists felt sure God didn't make things that way; there had to be some unifying principle to bring them together.

String theory emerged as a logical way to do it. "In the mid-1980s, we took it from a 'toy theory' to a major proposal of how nature might work," Strominger remembers.

The theory had its problems, however. It is possible to make more than one type of universe from strings, and there was no convincing way to explain how we got the one we live in.

Most physicists attacked this problem by starting from what they knew and trying to work through the equations until they reached a solution.

"I don't work that way," Strominger admits. "I think about the most aesthetically satisfying answer and work toward it. When you fail to guess right, it's usually because there's a nicer alternative. The way things finally came together was much more beautiful and powerful than anyone had imagined."

Getting in Phase

Strominger and his colleagues realized that there doesn't have to be a huge collection of string theories each of which produces a separate universe. Rather, all the theories are connected by phase transitions.

"It is crudely like the changes in water when it evaporates into vapor or freezes into ice," he explains. "Liquid water, vapor, and ice are not separate things; they are different phases of the same thing."

In 1995, Brian Greene of Cornell University, David Morrison of Duke University, and Strominger showed, by esoteric mathematics, that small black holes and subatomic particles like electrons and quarks are merely a matter of strings being in different phases.

Vafa described string science after this discovery as "boiling," "accelerating," and "exciting." He, Strominger, and others went on to demonstrate the possibility of phases of string theory that could produce the right kinds of particles and forces to make up a four-dimensional universe like our own.

"For every other theory that has been dreamed up, there's some way to show that it's not correct," Strominger points out. "The best thing you can say about string theory is that no one has been able to show it's wrong. The next step is to show that it's right."

Communing

When asked if he discusses string theory with his son, Jack Strominger laughs and says emphatically, "No way!" But the two still enjoy the same recreations they did when Andy and his brothers were kids: hiking and cross-country skiing.

Both remember how Andy got turned onto physics as a high school student at the Cambridge School of Weston in Massachusetts. There he met Mario Castillo, a physics teacher Andy describes as "brilliant and crazy. He communicated the beauty and excitement of the subject to me in a way I'll never forget."

When Strominger entered Harvard at age 16, however, he was more interested in idealism than physics. He divided his time between classes and a commune in southwestern New Hampshire.

"I wasn't much interested in the Harvard scene and was unconcerned about grades," he says.

Strominger dropped out of Harvard after his first year. But the idealism of the 1960s was dying and the commune disintegrated. He went back to Harvard and immersed himself in East Asian studies, taking intensive courses in Chinese until he spoke it fluently.

In 1975, Strominger was one of 20 American students invited by the Chinese government to visit that country. It was no sightseeing tour, however. He spent two months working in a commune, carrying buckets of fertilizer and working on an assembly line soldering batteries.

One day, Strominger, dressed in his factory uniform and cap, was in a noodle shop in Shanghai. He got into a conversation with a man who told him he had read in a newspaper about someone who had dropped out of Harvard to work on a commune. They laughed about the incongruity of it.

Instead of coming right back to the United States, Strominger went to Hong Kong and took a job with a Chinese-language newspaper. "I wrote stories about China and did some investigative reporting," he recalls.

When he returned to Harvard, Strominger thought about being a reporter, concentrating in East Asian studies, or going into physics. He had never stopped taking physics and math courses while studying Chinese. Physics won out.

Both Strominger families now live in Lexington and still enjoy hiking and cross-country skiing. Andy's daughters -- 12, 9, 7, and 4 years old -- delighted in seeing snow for the first time and building snow women. Andy often carries his 4-year-old in a backpack while he hikes.

Is he living the richer life he hoped for?

Strominger smiles and replies: "The faculty and students are wonderful. It's nice here. I'm happy."

Like string theory, it turns out to be a nicer alternative.