Boris Tsirelson died on the 21st of January 2020 in Switzerland, via assisted suicide after being diagnosed with high grade cancer. It is with great sadness that I type these news. I never met him personally, but I appreciate his work, and had several pleasant interactions with him online. As an undergrad student I asked him some inane questions about quantum correlations, that he patiently and politely answered. I also brushed with him on Wikipedia, where he was an avid contributor.
He was a famous mathematician, but his work in physics was not always recognized: the groundbreaking paper where he proved Tsirelson’ bound and started the characterization of the set of quantum correlations was published in 1980, but only started to get noticed by the time of the fall of the Soviet Union. Discouraged by the lack of interest, he decided to quit the field, and upon doing so made what he called his “scandalous failure”: asserted without proof that the set of quantum correlations generated by tensor-product algebras is equal to the set of quantum correlations generated by commuting algebras. Today this is known as Tsirelson’s problem, since asking the right question is more important than getting the right answer. The story was told much better by Tsirelson himself in a contribution to the IQOQI blog.
The solution of Tsirelson’s problem a mere week before his death was serendipitous. He was fascinated by the result, and concluded: “Envy me, I am very lucky. I am comfortably leaving during a peak of fame.”