Physics Nobel Goes to Francis Halzen, Who Turned a Cubic Kilometer of Antarctic Ice Into a Telescope

This year's Nobel Prize in Physics went to a scientist whose big idea was to bury light sensors deep in the ice at the South Pole and wait for some of the universe's most elusive particles to show up.

The Royal Swedish Academy of Sciences announced on Tuesday, Oct. 6, that Francis Halzen of the University of Wisconsin–Madison will receive the full prize "for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin." The award is worth 12 million Swedish kronor, about $1.2 million, according to Wisconsin Public Radio.

Catching "ghost particles"

Neutrinos have no electric charge and almost no mass, so they pass through ordinary matter almost without a trace. The Nobel committee's explainer notes that about 65 billion neutrinos from the sun stream through a person's fingernail every second. The much rarer ones that arrive with enormous energy from far outside the solar system can carry clues about violent cosmic events, such as the regions around supermassive black holes, where the most energetic cosmic rays are thought to be born.

Scientists had suggested decades ago that a huge volume of water could catch them, since a neutrino that occasionally hits an atomic nucleus produces a charged particle that gives off a faint blue light. In the 1980s, Halzen, who was born in Belgium in 1944, proposed using the naturally clear, dark ice of Antarctica instead. IceCube now uses thousands of sensors spread through a cubic kilometer of ice, buried as deep as about 2,500 meters (8,200 feet), according to WPR.

The payoff came in 2013, when IceCube announced the first detection of high-energy neutrinos from beyond the solar system, UW–Madison said. The observatory later tied a neutrino to a black hole at the center of a distant galaxy and found evidence of high-energy neutrinos coming from our own Milky Way. Nobel physics committee chair Mark Pearce said in an interview posted by the Nobel Foundation that the main sources still haven't been definitively identified.

Relief after years of waiting

"It was a great surprise, and I obviously didn't expect it," Halzen, 82, said by phone during the Stockholm announcement, as quoted by WPR. Speaking later by video from a hotel in Italy, where he was attending a scientific meeting, he told AFP that every October he had felt "miserable" when the prize went to someone else, worrying that he had let down the IceCube collaboration. "So that problem is finally solved," he said.

Halzen recalled that people once saw the project as "a cute idea" that "would never work," WPR reported. He credited roughly 450 collaborators in more than a dozen countries, according to AFP, and thanked the U.S. National Science Foundation, which funds the observatory, for taking a chance on it. WPR noted he is the first active UW–Madison faculty member to win a Nobel since 1975.