The next day, he started receiving emails from a famous Harvard mathematician, Shing-Tung Yau, inviting him to come and speak about his theorem. Zhang spoke at Harvard on May 13, the journal Nature announced the discovery online on the 14th, and a torrent of requests for interviews and invitations to speak began to pour in.
One lengthy article—complete with an animated mathematical sieve—about Zhang and his proof, was so popular that the Simons Foundation website, where it first appeared, crashed. Many comments online have expressed admiration for Zhang's pursuit of knowledge for knowledge's sake. "I may not need so much being famous," he says. "Maybe I will make more money. I don't care so much about these things."
In mathematical circles, the new advance presented an opportunity for further progress. Zhang had chosen 70 million as an arbitrary "bound" for the gap, expecting that other mathematicians would be able to take his modified sieve and narrow the gap further. They took up the challenge almost immediately, en masse and online. The project, called Polymath8, was launched by a renowned mathematician at UCLA named Terence Tao (two of his claims to fame: he won the Fields Medal, which has been dubbed the Nobel of mathematics, and he scored a 760 on the math SAT—at the age of 8). Dozens of mathematicians have worked on the project, thousands have visited its website, and so far, the gap has been reduced to 5,414.
Despite his continual mathematical mulling, Zhang does manage to squeeze in time for reading. He reads Shakespeare in Chinese and enjoys tackling popular classics like O. Henry stories and Jane Eyre in English. He also loves teaching—and his students seem to love him, too. One young woman he ran into on the bus congratulated him with a big hug.
The soft-spoken Zhang will tell a new acquaintance that he's shy, as he glances away. In front of 100 students or more, however, another side to his personality emerges, and many have commented on how funny he is in class. Some of his teaching techniques are both humorous and instructive. When the whole class is stumped by a difficult problem, he might say, "Suppose I forgot everything—and explain this problem to me." Trying to tell a genius how to do math is entertaining for students, and their attempts to do so reveal exactly what they do or don't understand at that moment.
As for the math behind his discovery, Zhang describes it as a kind of analysis, which is "deep, much deeper than calculus." Indeed, his proof, based on a strategy that Terence Tao describes as "audacious," has been a challenge even for other mathematicians to understand. Tao says that although the degree to which Zhang was "unknown" to the community of mathematicians has been exaggerated—he had published before—his position as an outsider may have helped him in this case because he ignored the prevailing opinion that the sieve wouldn't be powerful enough to achieve these results. "I would not be surprised if variants of Zhang's ideas will soon be used to attack other problems in number theory that had previously been considered beyond the reach of current technology," says Tao.
The requests for talks keep coming, and Zhang is taking off the fall semester to travel and speak about his discovery. Recently returned from China, he'll be speaking at Princeton and Berkeley this fall, and many other places in between. But he's not taking a break from research. He's started work on another intractable problem—he won't reveal which one—and proceeding in his usual manner. Using a computer sparingly for "some numerical parts," he writes a lot by hand. But the most important part of math research, he says, is this: "Mainly keep thinking." ~
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