Nuclear Clock: The Ticking Nucleus in the Search for Dark Matter ⚡ экспресс
Researchers have built a nuclear clock based on thorium-229, where a laser is locked to a nuclear transition (a change in the nucleus’s energy level) at a wavelength of 148 nm. The thorium nuclei are embedded in a calcium fluoride crystal at room temperature. The clock’s frequency stability is limited by shot noise and reaches 10^{-15} per day. With it, they constrained parameters of ultralight dark matter, rivaling the best atomic clocks. Much like how earthquakes expose Earth’s inner structure, the oscillations of the nuclear “ticking” could reveal the presence of invisible matter.
The most precise modern clocks count time by the oscillations of electrons in atoms. But their rhythm can be thrown off—like a mechanical watch's spring gets jolted by shaking. Physicists found a more reliable pendulum: the atomic nucleus. They took a thorium-229 nucleus, embedded it in a crystal, and coaxed it to oscillate by shining a laser at a very specific frequency. This technique is called spectroscopy—essentially, finding the right rhythm to get the pendulum swinging. And the nucleus responded: it vibrates 2,000 trillion times a second—a million times faster than the quartz in your smartphone.
The precision is staggering: over a day, the error is one billionth of a billionth of a second. Such a clock would be off by just a second over 30 billion years. But the real kicker is that this pendulum is exquisitely sensitive to any 'breath' from the outside world, such as passing particles of dark matter. Scientists searched for its traces—periodic nudges or a smooth drift in frequency. They found nothing, but that's a result too: now we know just how weakly dark matter can interact with ordinary atomic nuclei.
In the future, the accuracy of these solid-state clocks will multiply many times over. They'll test whether the fundamental constants of the standard model are truly constant, and perhaps even notice that time flows differently at different heights—just as Einstein predicted. For now, their main mission is to catch the 'shadow' of dark matter.
🎯 The transition in the thorium-229 nucleus is the only one in the universe that can be 'caught' with today's laser technology. That's why it was chosen for the first nuclear clock.