T. Kobayashi

A high-speed collision knocked a neutron out of a helium-8 nucleus, and for an instant a helium-7 nucleus appeared, like an overloaded shelf shedding three books at once. This fleeting 'sound' of decay was captured for the first time: three neutrons flew apart, leaving behind an ordinary helium-4 nucleus.

Deep beneath Japan's Mount Ikeno sits a tank holding 50,000 tons of the purest water. Inside, it catches neutrinos — ghostly particles that zip through Earth as if it weren't there. When a star explodes in our galaxy, neutrinos arrive first, hours before the light.

Inside every atom lives a proton. For a long time, it was considered as eternal as matter itself. But theories that unify all forces of nature predict that, sooner or later, the proton will decay. The only question is how long we have to wait. In the Japanese detector Super-Kamiokande — a giant tank of ultra-pure water — physicists searched for signs of such a decay.

Two tin nuclei collide at about two-thirds the speed of light. For an instant, a hot, dense cloud forms, and protons fly out in all directions. If you catch pairs of protons and measure how often they fly off in the same direction, you can work out the size of that cloud. This method is called femtoscopy: it works like a microscope for nuclear scales.

Inside an atomic nucleus, protons and neutrons don't sit still like peas in a pod. Each particle occupies its own orbit — a region of space where it can be found. The larger the orbit, the more 'smeared out' the particle is.