Initial results from the world’s first two working nuclear clocks indicate that China’s timepiece is about six times as stable as the one in Vienna, according to papers published this week by the journal Nature. The clocks were developed independently but both the Chinese team, led by Tsinghua University in Beijing, and the researchers at Vienna’s TU Wien used thorium-229 nuclei embedded in crystals to keep time by the steady rhythm of the atom’s core, rather than the electrons whirling around...