In the last months of his life, Gambhir acknowledged that his own luck had run out. “I tell my wife, ‘If I just had more time, I know I could solve this,’” he told me last fall. I asked him how much time he would need to solve his own cancer case. His answer, fittingly, was “decades.”

This was not the first time for Gambhir that the gap between his futuristic vision and the present came with tragic personal consequences. When he and I met in November, he wore a thin, red, braided cloth bracelet: the kalava, a symbol of protection in Hinduism. “I’m not a religious person at all,” he said, gazing down at his wrist. “It’s a connection to my son.” In 2015, Sam and Aruna Gambhir lost their only child, 16-year-old Milan, to an aggressive and highly lethal brain tumor called glioblastoma multiforme, one of the many cancers that Gambhir had been studying at the time in his lab.

As the Gambhir family learned afterward, Milan’s cancer was likely tied to Li-Fraumeni syndrome, a rare, inherited condition caused by a genetic mutation that dramatically raises the risk of many types of cancer. The mutation was passed down from Aruna, who has twice battled breast cancer as a result of the DNA defect. “If [Milan] had been born 100 years from now,” Gambhir said in a 2018 talk, “the tools of precision health would possibly have allowed him to live much, much longer.”

In the final months of Milan’s life, Gambhir confided to family members and close friends that he felt as if his mind had “opened.” His scientific imagination, already expansive, seemed to stretch even further, with an invigorated sense of purpose. Unlike Milan, Gambhir carried no family history of cancer, so he had no reason to expect that the many productive years he had left in his career would be cut short. “I thought we had had enough random bullets with our son,” he told me. Still, he said, it had been easier to come to terms with his own untimely diagnosis than with his child’s. “When your son’s life is at stake, it’s even more than your own life.”

Just before Thanksgiving last year, Gambhir learned that the cancer that had been confined to his bone marrow had spread. He was in severe pain. “I’m back to square one,” he told me by phone in December. “Just have to bear through it.” By January, it was obvious that his cancer had metastasized.

As the coronavirus pandemic seeded itself around the world, Gambhir entered his own medical lockdown, sequestered at home as he cycled over the subsequent months through different chemo regimens, suffering toxic reactions to almost all of them. “With Sanjiv, the problem was that he knew too much … But he still had hope,” Aruna told me in August. “He was fighting until the very end.”

Early in our conversations, Gambhir admitted that living in the present moment—that earnest cultural cliché—was “a foreign concept” to him. Later in our talks, I mentioned that the idea of time, in all of its dimensions, seemed to course through his work. He agreed. “The part that humans can’t comprehend—and I myself have a difficult time comprehending it—is time. We are a tiny speck in this massive universal clock.” That enormity, he added, worked against him. “It’s frustrating, because from the pure scientific-discovery part, you would like to be able to … [go] back to that full movie.”