Mathematician Yitang Zhang: why did I return to China at 70?

Yitang Zhang () emerged as a prominent mathematician in 2013 with his groundbreaking work on the Twin Prime Conjecture, proving that there are infinitely many pairs of primes with gaps less than 70 million. His paper, entitled 'Bounded Gaps Between Primes', was accepted by Annals of Mathematics in just 3 weeks-an exceptionally rare feat in the field of mathematics. Overnight, Zhang, a previously obscure 58-year-old lecturer at a US university, became a globally celebrated academic luminary. He was once a top student in Peking University's mathematics department, but after struggling through his PhD program in the USA, he failed to secure an academic position, and worked at a Subway restaurant for 7 years before a friend helped him land a position as an assistant professor at the University of New Hampshire. Until his 2013 breakthrough, he remained a lecturer. This legendary journey earned him the nickname 'the Hidden Master of Mathematics'. In Chinese martial arts stories, the hidden master often passes on his lifelong skills to a destined young man in his twilight years. When asked by National Science Review (NSR) why he chose to return to China in 2025 at the age of 70 to work at the Hong Kong Institute of Advanced Study of Sun Yat-sen University, one reason he gave was his hope to pass down the mathematical insights he had accumulated over decades and 'mentor a group of young talents' in China. For Zhang, returning to China is about academic legacy, and also a natural choice-he believes China's scientific capabilities are undergoing a qualitative transformation, making it one of the most conducive places for basic research in the world. In this interview with NSR, Zhang also discussed the ancient and captivating field of analytic number theory, his views on mathematical research methods, mathematical education and the temperament of mathematicians.