Researchers in Vienna and Beijing have independently built the first nuclear clocks based on oscillations inside thorium nuclei, marking a major milestone for a field that could eventually produce highly portable, ultra-precise timekeepers. The clocks are already precise enough to lose only about a second over millions of years. The New York Times reports: The first nuclear clocks are not going to immediately supplant the worldwide network of atomic clocks, whose steady ticking we rely on for GPS and the definition of a second. Nor have they captured the record for most precise timepiece; the best atomic clocks are about 10,000 times more reliable and would take more than 100 billion years to lose one second. But nuclear clocks hold a bevy of potential advantages over existing atomic clocks. One day, they could be more reliable than the leading atomic versions, and nuclear clocks could be made more portable. They even hold the ability to search for certain kinds of dark matter -- the invisible stuff whose clumps make up 83 percent of the matter in the universe. If a particle of dark matter passed through the thorium nuclei, it could register as a wobble in the nuclear clock's otherwise steady ticktock. The findings have been published in the journal Nature.Read more of this story at Slashdot.