Scientists have invented the world’s first nuclear clocks that they say could unlock the fundamentals of physics. The two devices are the newest atomic clocks, which measure time by monitoring light by using transitions occurring inside the atomic nucleus, involving protons and neutrons. Atomic clocks have been used to keep precise measures of time and were first created in 1949 and, despite the name, do not use nuclear fusion or fission. The world’s best clocks have relied on electrons jumping between energy levels in atoms but the discovery has shown that the reference for a clock can come from the nucleus itself. The research teams from China’s Tsinghua University and other institutions in the country and Austria’s TU Wien reported their breakthroughs separately in two papers published in Nature on Wednesday. The clock uses thorium-229, a rare atom whose nucleus can switch energy states using ultraviolet light from a laser. It is the only nucleus known to work this way.The team built a laser that makes ultraviolet light at 148.4 nanometres and aimed it at small calcium fluoride crystals containing thorium-229.The key finding was that the nuclear clocks worked. The laser stayed locked to the thorium-229 nucleus and kept steady time, reaching a precision of about one part in a quadrillion (10⁻¹⁵) over the test period. While precise timekeeping is vital for everyday technologies such as satellite navigation and telecommunications, nuclear clocks could make these systems more preciseThey could also be important in fundamental physics, the paper reads, however, it does not specify the exact use cases.