Imagine an hourglass where the sand grains transform into other grains as they fall: that's what unstable atomic nuclei are like. They live for an instant and then decay, ejecting an electron (this is beta decay). In September 2025, theorists and experimentalists gathered under the FRIB Theory Alliance to discuss how to use such decays to probe the structure of matter.

The FRIB accelerator (USA) can create short-lived isotopes that don't exist on Earth but are found inside exploding stars. By measuring how fast and with what energy they decay, physicists test theories of nuclear forces. One of the main goals is to understand why the universe has more matter than antimatter. To this end, they search for tiny deviations from expected symmetry in the weak interaction that governs beta decay.

Currently, scientists use complex computer models to calculate the behavior of dozens of particles inside the nucleus. But accuracy still lags. At the meeting, they agreed to join forces: experimentalists will provide new data on rare isotopes, and theorists will improve their calculations. Then, perhaps, we'll be able to peer into the heart of a supernova and see how heavy elements like gold are forged. Just like in that hourglass, where each falling grain is a step toward unraveling the cosmic mechanism.