Two scientists from Japan and from Canada have won the Nobel Prize for Physics for their discoveries related to the elusive, fast-moving neutrino.
Takaaki Kajita, director of the Institute for Cosmic Ray Research and professor at the University of Tokyo, shared the €857,000 prize with Arthur McDonald, professor emeritus at Queen's University in Canada.
Neutrinos are fundamental particles but they are of particular interest to scientists because they are very difficult to capture.
They are like an electron but do not carry an electrical charge, so they are difficult to control.
They are also almost massless and do not react with ordinary matter as they travel away from their sources in the sun and deep space at near the speed of light.
Trillions pass through us and the Earth every second but leave no evidence of their passing.
Three types
The scientists won the prize for discovering that there are actually at least three types of neutrinos and that they could “flip” from one type to another in what is known as “neutrino oscillation”.
This finding in turn proved that the particles must have some mass, even if this is only a very tiny amount.
"The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe," the Royal Swedish Academy of Sciences said, in a statement issued on Tuesday.
The two scientists worked separately. Mr Kajita worked at the Super-Kamiokande detector in Japan and Mr McDonald at the Sudbury Neutrino Observatory in Ontario, Canada.
This allowed them to watch neutrinos transform when coming from deep space and from the sun.
The particles were captured by very large detectors located deep underground.
"Yes, there certainly was a Eureka moment in this experiment, when we were able to see that neutrinos appeared to change from one type to the other in travelling from the sun to the Earth," Mr McDonald told a news conference in Stockholm.
