Francis Halzen Wins Physics Nobel for IceCube Neutrino Work

Scientists have known since the early twentieth century that cosmic rays (energetic particles from space, mostly protons and atomic nuclei) constantly bombard Earth. Some carry more energy than the Large Hadron Collider, the world's most powerful particle accelerator, can produce. Because cosmic rays carry electric charge, magnetic fields in space bend their paths. This makes it impossible to trace them back to their source. Scientists needed a different cosmic messenger. Neutrinos are nearly massless, electrically neutral subatomic particles that barely interact with matter. Trillions pass through our bodies every second without effect. They travel in straight lines from violent cosmic events such as exploding stars or black-hole-powered jets. This makes them ideal tracers of the universe's most energetic phenomena.

The idea of using a large natural volume of water or ice to catch neutrinos dates to the 1960s. Early attempts to build a detector in the Pacific Ocean failed because maintaining instruments underwater proved too difficult. A Soviet-era plan to study neutrinos in Antarctic ice was also judged unsuitable for the very high energies scientists wanted to study. In 1988, physicist Francis Halzen proposed a fresh approach. He suggested using the thick, transparent ice sheet at the South Pole itself as a giant particle detector. The concept grew through smaller trial projects before the full-scale observatory was built.