By Jacob Aron and Katia Moskvitch Mathematics is a universal language. Even so, a Kazakh mathematician’s claim to have solved a problem worth a million dollars is proving hard to evaluate – in part because it is not written in English. Mukhtarbay Otelbayev of the Eurasian National University in Astana, Kazakhstan, says he has proved the Navier-Stokes existence and smoothness problem, which concerns equations that are used to model fluids – from airflow over a plane’s wing to the crashing of a tsunami. The equations work, but there is no proof that solutions exist for all possible situations, and won’t sometimes “blow up”, producing unrealistic answers. In 2000, the Clay Mathematics Institute, now in Providence, Rhode Island, named this one of seven Millennium Prize problems offering $1 million to anyone who could devise a proof. Otelbayev claims to have done just that in a paper published in the Mathematical Journal, also based in Kazakhstan. “I worked on the problem on and off, for 30 years,” he told New Scientist, in Russian – he does not speak English. However, the combination of the Russian text and the specialist knowledge needed to understand the Navier-Stokes equations means the international mathematical community, which usually communicates in English, is having difficulty evaluating it. Although mathematics is expressed through universal symbols, mathematics papers also contain large amounts of explanatory text. “Over the years there have been several alleged solutions to the Navier-Stokes problem that turned out to be wrong,” says Charles Fefferman of Princeton University, who wrote the official formulation of the problem for Clay. “Since I don’t speak Russian and the paper is not yet translated, I’m afraid I can’t say more right now.” Otelbayev is a professional, so mathematicians are paying more attention to his proof than is typical for amateur efforts to solve Millennium Prize problems, which are regularly posted online. The Russian-speaking Misha Wolfson, a computer scientist and chemist at the Massachusetts Institute of Technology is attempting to spark an online, group effort to translate the paper. “While my grasp on the math is good enough to enable translation up to this point, I am not qualified to say anything about whether or not the solution is any good,” he says. Stephen Montgomery-Smith of the University of Missouri in Columbia, who is working with Russian colleagues to study the paper, is hopeful.”What I have read so far does seem valid,” he says “but I don’t feel that I have yet got to the heart of the proof.” Otelbayev says that three colleagues in Kazakhstan and another in Russia agree that the proof is correct. Understandably, a high burden of proof is required to claim the $1 million prize. Clay’s rules say the solution must be published in a journal of “worldwide repute” and remain unchallenged for two years before it can even be considered. Nick Woodhouse, president of the Clay Mathematics Institute, declined to comment on Otelbayev’s proof. “It is currently being translated by my students, and will be available soon,” says Otelbayev. He says that he will publish it again once it is translated into English – initially in a second Kazakh journal, and then perhaps abroad. To date, only one Millennium Prize problem has been officially solved. In 2002, Grigori Perelman proved the Poincaré conjecture, but later withdrew from the mathematical community and refused the $1 million prize. A possible solution for another problem, known as P vs NP, caught mathematicians’ attentions in 2010,