When the infinitely small determines the infinitely large ⚛️

Dark matter, this "invisible glue" that ensures the cohesion of galaxies in the Universe, has long intrigued scientists, but a major discovery could help solve the mystery.


Thanks to the discoveries made by astronomer Edwin Hubble in 1929, we know that the Universe has been expanding since its birth. But subsequent measurements of the speed of this expansion have revealed a mystery that has fascinated the scientific community for decades: according to the laws of physics, the observable mass of the Universe is clearly insufficient to account for the measured speeds.

To explain the phenomenon, many researchers postulated, as early as the 1930s, the existence of "dark matter," an undetectable material by conventional means, which would make up nearly 85% of the total universal mass and would allow the cohesion of structures like galaxies.

Among the hypotheses put forward to describe the nature of this unknown matter are axions, theoretical particles initially proposed to solve the problem of strong charge-parity (CP) symmetry in the Standard Model of physics. These particles, which research has been trying to uncover for over 40 years, would have been generated at the time of the Big Bang.

It was while attempting to observe them that the international team, including Professor Maia Vergniory from the Faculty of Science at UdeS, made a decisive experimental breakthrough, bringing science closer to proof of their existence. Professor Vergniory thus co-authors a major advance whose results could shed light on our understanding of one of the greatest mysteries of our time and are the subject of a publication in the prestigious journal Science this Friday, January 10, 2025.

"This is an extraordinary advance because, in addition to explaining an important mystery of our natural history, this breakthrough has the potential to generate substantial technological gains. The crystals we designed for our experiment are capable of guiding photons to their edges in a single direction, without drifting—a property essential for data transmission, which could also reduce the risk of errors in quantum computing," explains Professor Maia Vergniory, Faculty of Science.

To achieve this breakthrough, the team first imagined and designed geometric crystalline structures made from a synthetic material chosen for its magnetic and optical properties, yttrium-iron garnet.

The team observed that, on the three-dimensional edges of these structures, photons moved in a unidirectional manner—for example, upward, forward, and to the right—without experiencing phenomena such as backward scattering. However, this behavior of photons in the crystal also corresponds to what the theory predicts for axions, suggesting that the observed photons are, in fact, axions converted into photons.

"We are thus getting closer to the day when we can prove their existence through direct observation, which would be a significant advance in our understanding of dark matter," says Professor Maia Vergniory.

The next step for the team will be to optimize their crystalline structures to use them in experiments aimed at detecting photons converted from axions under extreme conditions, such as powerful magnetic fields.

Three theoretical candidates to explain dark matter

Dark matter is a mysterious material detectable only by the gravitational effects it exerts on its surroundings. While it has not yet been directly observed, three theoretical particles are candidates to explain its existence:
- Axions: hypothetical light particles generated at the time of the Big Bang.
- WIMPs (Weakly Interacting Massive Particles): massive particles that interact weakly.
- MACHOs (Massive Compact Halo Objects): compact objects such as dead stars or black holes (now considered insufficient to explain dark matter).

The research to which Maia Vergniory contributed mobilized many people across three continents. Led by Professor Zhang Baile of Nanyang Technological University (Singapore), it also brought together researchers from the Max Planck Institute for Chemical Physics of Solids (Germany), the Swiss Federal Institute of Technology Zurich (Switzerland), the Donostia International Physics Center (Spain), the University of the Basque Country and the Basque Foundation for Science (Spain), Dongguan University of Technology (China), Nanjing University (China), the Southern University of Science and Technology (China), the University of Electronic Science and Technology of China, and Westlake University (China).