Nobel Prize for Physics 2015: How two scientists changed our understanding of particle physics
The 2015 Nobel Prize has been awarded to two scientists who helped reveal that neutrinos, one of the most enigmatic subatomic particles in our universe, have mass.
Takaaki Kajita from the University of Tokyo in Japan won half the prize, while the other half went to Canadian physicist Arthur McDonald.
At the Royal Swedish Academy of Sciences ceremony in Stockholm, the pair were praised for their “discovery of neutrino oscillations”, which show that the particles are capable of changing identities. As mass is a fundamental requirement for metamorphosis of this kind, the findings revealed that neutrinos must therefore be made of physical matter.
The consequences of this could be huge, and according to the Nobel Prize Assembly, it has “changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe”.
For a long time, neutrinos were considered mass-less because the number of neutrinos that scientists estimated should be present in the universe according to calculations did not match up to what they were able to measure, The reason, it now turns out, was not that the neutrinos didn't exist but that they had changed into something else entirely.
A neutrino puzzle that physicists had wrestled with for decades had been resolved. Compared to theoretical calculations of the number of neutrinos, up to two thirds of the neutrinos were missing in measurements performed on Earth. Now, the two experiments discovered that the neutrinos had changed identities.
So how did the two scientists do it? In the case of Kajita, he discovered that neutrinos from the atmosphere switched between states as they travelled towards the Super-Kamiokande detector in Japan.
Arthur McDonald, meanwhile, demonstrated that neutrinos coming from the Sun to the Earth did not disappear on their way – they just arrived on earth with a different identity.