For the first time, researchers have built working nuclear clocks that tick using the energy of an atom's nucleus, not its electrons. Two independent teams, one in the United States and one in Austria, have unveiled these long awaited timekeepers. They promise precision that could eventually surpass the world's best atomic clocks by a factor of ten or more.
A clock that uses the heart of an atom
Atomic clocks, the current gold standard, measure time by counting the vibrations of electrons as they jump between energy levels. Nuclear clocks do something similar but use the nucleus itself. The nucleus is far less sensitive to outside disturbances like magnetic fields or temperature changes. That stability could make nuclear clocks extraordinarily accurate. The key ingredient is a rare isotope of thorium, thorium 229, which has a unique low energy state that can be triggered with a laser.
Two teams, two approaches, one breakthrough
Researchers at the Joint Institute for Laboratory Astrophysics in Boulder, Colorado, built one version. They embedded thorium atoms in a crystal of calcium fluoride and used a special ultraviolet laser to excite the nuclei. A separate group at the Vienna University of Technology in Austria took a different path. They trapped individual thorium ions in an electric field and hit them with laser light. Both teams succeeded in making the nuclei tick, producing a measurable signal that can be used to keep time. The results were published in Nature.
Why this matters beyond better clocks
For physicists, nuclear clocks are not just about telling time more precisely. They could become powerful tools for testing fundamental theories. Because the nucleus is so isolated from its surroundings, any tiny change in its ticking rate could reveal new forces or particles that standard physics does not account for. Some researchers hope nuclear clocks could detect variations in the fundamental constants of nature, something that would shake the foundations of modern physics. The technology is still in its infancy, but the first ticks have been heard.
A new era of timekeeping begins
The arrival of working nuclear clocks marks a genuine milestone in experimental physics. For decades, the idea existed only on paper. Now it is real. The clocks are not yet ready to replace atomic time standards, but they have crossed the threshold from theory to practice. That alone is a significant achievement. What these clocks will reveal about the universe remains to be seen, but the ticking has started.
