Ways to weigh a neutrino
In 1980, Hamish Robertson was a tenured professor at Michigan State. He’d been there since his postdoc in 1971, and he was content. “I want to stress how valued and happy I felt there,” he says. “It was, and still is, an outstanding place.”
But he and his friend and colleague, Tom Bowles, had begun to hatch an idea that would take him far from MSU. They were devising a new experiment to measure the mass of the elusive and perplexingly light neutrino.
Neutrinos are the only fundamental particles whose mass we still don’t know. As their name implies, neutrinos are very, very small. But they outnumber the other fundamental particles by a factor of 10 billion.
Their collective abundance makes it likely that they influenced the formation of structures in the early universe, so knowing their mass is critical to closing gaps in our understanding of the cosmos.
But how do you measure something with a mass so small it approaches zero? Hundreds of physicists, including Robertson, have devoted their careers to solving this problem, and they’re seeing progress. Research projects underway in Europe and the United States fuel a sense of optimism that the task can be accomplished.
