In April 2013, editors at Annals of Mathematics, one of the world’s most prestigious mathematics journals, received a paper titled "Bounded Gaps Between Primes" from a little known mathematician, then an adjunct professor at the University of New Hampshire in the U.S.

The paper addressed one of mathematics’ oldest problems related to prime numbers, showing that infinitely many pairs exist with a gap of less than 70 million. Within three weeks, in an unusually fast review process, expert reviewers confirmed that Zhang had proved "a landmark theorem in the distribution of prime numbers," according to Quanta Magazine.

The result quickly drew global attention, turning Zhang, then 55, into a prominent figure in mathematics. His work has since been regarded as one of the most important advances in number theory in the 21st century.

"He is not a fellow who had done much before. Nobody knew him." Peter Sarnak, Professor in the School of Mathematics, said in a 2014 interview with the U.S.’s Institute for Advanced Study. "His result was spectacular."

Following the breakthrough, Zhang traveled internationally to give lectures, received multiple awards, and was featured in major publications. His journey was also documented in the film "Counting From Infinity" directed by U.S. filmmaker George Paul Csicsery and released on Jan. 10, 2015.

Years of struggle

Born in 1955 in Shanghai, Zhang grew up in an academic household. His father was a university professor and electrical engineer, and his mother worked as a civil servant. He showed early mathematical talent, proving the Pythagorean theorem at around the age of nine and understanding Fermat's Last Theorem and the Goldbach conjecture by 10 years old.

Zhang enrolled at Peking University, where he became one of the country’s top math students, earning both bachelor’s and master’s degrees. He later pursued a PhD at Purdue University in the U.S. under mathematician T. T. Moh, but after defending his dissertation in 1991, he struggled to secure an academic position.

In the documentary "Counting From Infinity," Zhang said his doctoral adviser did not write recommendation letters for him and acknowledged that his quiet personality made it difficult to build professional connections. Zhang told the South China Morning Post that the collapse of the Soviet Union during that time led to an influx of highly trained scientists into the U.S., making academic jobs "incredibly difficult" to obtain at the time.

"I did not give up because I felt that I could continue to research mathematics, which can be done anywhere."

During this period, he lived in hardship, sometimes sleeping in his car and working for about seven years in various odd jobs, including food delivery, working at a Subway sandwich shop where he kept books, took orders and even made sandwiches. In 1999, he secured a temporary teaching position at the University of New Hampshire with help from a former classmate from Peking University.

"I was born for math," he told the Institute for Advanced Study. "For many years, the situation was not easy, but I didn’t give up. I just kept going, kept pushing. Curiosity was of first-rank importance––it is what makes mathematics an indispensable part of my life."

There, he shifted his focus to number theory, working under unstable contracts without research support until becoming a full-time lecturer in 2005. He often used bus commutes to think about mathematical problems.

Yitang Zhang delivers a lecture at Nankai University, China. Photo courtesy of the university

Returning home

Zhang spent three years working on the bounded gap problem without finding a door. Then on July 3rd 2012, while walking near a friend’s home in Colorado, he discovered a way forward. He spent the next eight months refining the work and two additional months reviewing it independently, as no one he knew understood it, before submitting the paper to Annals of Mathematics.

He did not expect it to be accepted so quickly. The day after its acceptance, emails flooded in, followed by invitations. He said he accepted some invitations but what he wanted was to "just keep quiet and live a very quiet, very peaceful life."

Mathematicians who met Zhang described him as reserved and deeply focused, noting both the difficulty and impact of his work. Matthew Emerton, a professor of mathematics at the University of Chicago who met Zhang at Princeton, said Zhang later earned another prize for his work but remained humble.

"Probably most mathematicians are very low-key about getting a prize, because you’re not in it for the prize, but he seemed particularly low-key. It didn’t seem to affect him at all."

Now 71, Zhang joined Sun Yat-sen University in Guangzhou as a full professor in June 2025, after leaving the University of California, Santa Barbara. He said many Chinese scholars in the U.S. have returned or are considering returning, calling it a "positive trend," and noted that funding cuts under U.S. President Donald Trump’s administration had left researchers in a "tough situation."

He said he accepted the position after receiving multiple invitations from universities in China, adding that he was touched when a customs officer came on board to greet him upon landing.

"It felt like the country valued and respected me highly," he told SCMP. "Forty years later, I am back to my starting point, working in and serving my country."