Earlier this year, two teams of scientists experienced simultaneous breakthroughs in timekeeping technology by utilizing nature’s most precise metronome: an atom’s nucleus. This advancement comes after increasing worry about the accuracy of atomic clocks, which use the resonant frequencies of Cesium-133 electrons to measure the passing of time. On June 3, a team of researchers in Vienna published their findings , and four days later, a team in Beijing followed with similar research . These new clocks, which use the Thorium-229 nucleus, pave the way for numerous scientific inquiries such as proving general relativity, understanding the nature of dark matter, and allowing us to travel the cosmos.

In 2024, a team at the University of Colorado demonstrated the capabilities of nuclear clocks, although this June marked the first time one had been fully realized. If previous atomic clocks had been running for 150 million years, they would have either lost or gained a fraction of a second . This might seem minuscule, but extreme precision is necessary for GPS technology, banking systems, stock trading, telecommunications, and other critical infrastructure. Thorium-229 is especially great for nuclear clocks because it has a relatively low resonant frequency . When the Thorium-229 nucleus is struck by a laser with this specific frequency, its protons and neutrons jump into higher energy levels. Think of the atomic nucleus as a wine glass, which has its own natural vibrational frequency, that when matched by a singer, can shatter it. The same thing happens within the Thorium-229 nucleus: it gains energy until it excites.

Nuclear clocks keep time much more accurately than their electron counterparts. The frequency needed to excite Cesium-133 electrons is much smaller than that of the Thorium-229 nucleus. One second, according to the National Institute of Standards and Technology, is defined as the amount of time it takes for a Cesium-133 atom’s electrons to be excited 9,192,631,770 times. However, the number of excitations per second within the Thorium-229 nucleus is roughly 2,020,407,384,335,000 times, six orders of magnitude more accurate than current atomic clocks.

Two of the most famous theories in physics — Einstein’s theory of relativity and the existence of dark matter — are among what we could test with a device of this precision. The theory of relativity, exhibited in blockbuster movies like “Interstellar,” states that gravity not only warps space but also time itself. Although this theory is the more well known of the two, perhaps the more striking tests would be understanding the nature of dark matter. It has been observed that the masses of galaxies are too small to account for the gravitational effect they exert, suggesting an invisible source of additional mass . Dark matter is believed to account for up to 85% of the mass of all matter in the universe and in certain denser patches may adjust what have long been deemed fundamental constants , like the fine-structure constant, particle masses, and Newton’s gravitational constant.

Nuclear clocks would also be a necessary step for interplanetary travel . To land a crewed mission on Mars, our clocks would need to be much more accurate than today’s, and this gap only becomes more apparent the further you travel. Deep-space navigational technology would also need to be self-reliant, meaning future research in nuclear clocks could focus on ways to make them smaller, lighter, and more resilient to environmental changes. There is much work to be done before any of these applications can come to fruition, but the research done by the teams in Austria and China is an extraordinary leap toward knowledge that could alter our current understanding of the universe.