In the icy vastness near the South Pole, thousands of sensors scan space searching for answers about the existence of quantum gravity.
These sensors are part of the IceCube Neutrino Observatory, located next to the Amundsen-Scott Station in Antarctica. They monitor neutrinos, particles that are almost massless and without electric charge, coming from space. A team from the Niels Bohr Institute (NBI) at the University of Copenhagen has developed a method using data from these neutrinos to explore the presence of quantum gravity.
Physicists attempt to unify two distinct fields: classical physics, which explains gravity and our everyday environment, and quantum physics, which describes the atomic world. Tom Stuttard, assistant professor at the NBI and co-author of a paper in the journal
Nature Physics, speaks of this quest for unification as one of the major challenges in fundamental physics.
Their study reviewed over 300,000 neutrinos, primarily from the Earth's atmosphere, resulting from collisions between high-energy space particles and molecules like nitrogen in our atmosphere. These neutrinos are easier to study than those from deep space because they are more numerous, which validated their methodology. Now, the team is ready to move to the next phase: studying deep-space neutrinos.
The IceCube Neutrino Observatory is unique because it allows space observation from the Earth's opposite hemisphere, as neutrinos can travel through our planet without disturbance. More than 300 scientists from various countries participate in this project.
Neutrinos, capable of traveling billions of light-years through the Universe without alteration, could reveal clues about quantum gravity if they undergo subtle changes during their journey. Neutrinos exist in three forms or "flavors": electron, muon, or tau neutrinos. Their ability to change flavor while traveling, a phenomenon known as neutrino oscillation, is a quantum behavior that could be disrupted by quantum gravity.
The study published in
Nature Physics did not find any changes related to quantum gravity in atmospheric neutrinos, but this does not mean they do not exist. The distances traveled by these neutrinos are relatively short compared to interstellar distances, and a longer range might be necessary to observe an impact of quantum gravity.
Researchers remain optimistic. Thanks to their methodology and the anticipation of future measurements with astrophysical neutrinos, as well as the development of more accurate detectors, they hope to definitively answer the question of the existence of quantum gravity.