TOKYO -- One of the great unsolved mysteries of physics is that current science can account for just 5% or so of the mass of the universe. The rest consists of so-called dark matter and dark energy, which scientists cannot yet explain. The proof that neutrinos have mass -- what the winners of the 2015 Nobel Prize in physics achieved -- could contribute toward solving that mystery.
Another major challenge in physics is that both particles and corresponding antiparticles should have been created in the Big Bang, but almost all of the antiparticles have disappeared. Though theories have emerged that explain most of this asymmetry, some gaps remain. The odd behavior of neutrinos offers a clue to filling them in.
Standard Model upended
Neutrinos are subatomic particles that pass through matter with minimal interaction. Though vast quantities of neutrinos stream to Earth from space, they are extremely difficult to detect. It had been believed since their discovery in the 1950s that they have no mass.
Takaaki Kajita of Japan and Arthur McDonald of Canada disproved this theory. Neutrinos come in three types, or "flavors": electron, muon and tau. Kajita observed the particles at the Super-Kamiokande facility, located 1,000 meters underground in the Kamioka mine in Japan. He noticed in 1998 that more muon neutrinos were detected coming in directly from the atmosphere than from below, passing through the Earth.
This discovery indicated that some muon neutrinos passing through the Earth were changing into tau neutrinos. Meanwhile, in Canada, McDonald found proof that the electron neutrinos generated by the sun also change flavors. This phenomenon, called neutrino oscillation, is possible only if neutrinos have mass.
The Standard Model of particle physics developed in the second half of the 20th century is used to explain the origin of the universe and matter. The discovery of the Higgs boson, the subject of the 2013 Nobel physics prize, was believed to complete the theory. But the Standard Model relies on the assumption that neutrinos are massless. Kajita and McDonald's results show that a replacement is needed. Detailed examination of the properties of neutrinos will let scientists develop an even more robust model.
Kajita's mentor was Masatoshi Koshiba, distinguished professor of the University of Tokyo. Koshiba, working at the predecessor of the Super-Kamiokande detector, was the first to observe neutrinos arriving from the distant reaches of space after being generated by a supernova, an achievement for which he received the 2002 physics Nobel.
This year's Nobel Prize in chemistry has been awarded to Aziz Sancar of the U.S, Tomas Lindahl of Sweden and Paul Modrich of U.S. for their work on mapping how cells repair damaged DNA and safeguard genetic information at the molecular level.
Sancar, who was born in Turkey, mapped what is called the nucleotide excision repair, a mechanism that cells use to repair ultraviolet damage to DNA. Sancar is a Sarah Graham Kenan professor of biochemistry and biophysics at the University of North Carolina School of Medicine in the U.S.
Lindahl showed that contrary to previous understanding, DNA decays at a rapid pace, which led him to discover a molecular machinery that constantly counteracts the collapse of DNA.
Modrich demonstrated how the cell corrects errors that occur when DNA is replicated during cell division, a process that occurs several million times every day in the human body.
"The Nobel laureates have provided fundamental insights into how cells function, knowledge that can be used in the development of new cancer treatments," the award-giving body said in a press release.