This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Are the laws of physics truly the same everywhere in the universe? This fundamental principle, known as Lorentz invariance, lies at the heart of Einstein's theory of relativity.
Yet some theories that seek to reconcile gravity with quantum physics suggest that it might not always hold. To investigate this possibility, researchers from the international KM3NeT collaboration analyzed 5,828 atmospheric neutrino candidate events detected by KM3NeT/ORCA, a neutrino telescope located deep in the Mediterranean Sea. They found no evidence of a violation, but were able to set new experimental limits on how large such effects could be, including the first direct constraints on certain possible differences in the behavior of muon and tau neutrinos.
The results are published in the Journal of Cosmology and Astroparticle Physics. Why question such a fundamental principle? One reason lies in the search for a theory of quantum gravity, capable of reconciling general relativity with quantum physics.
Some theoretical approaches suggest that spacetime, which we normally consider continuous, might actually be made up of extremely small, discrete units. This could have profound implications for the laws of physics, potentially including violations of Lorentz invariance. "We still don't know whether our spacetime is continuous or might be discrete," explains Alba Domi, a researcher at Erlangen Centre for Astroparticle Physics (ECAP), Friedrich-Alexander-Universität Erlangen-Nürnberg, and one of the study's two corresponding authors.
"Looking for violations of Lorentz invariance is one way to investigate this possibility." Neutrinos are particularly promising probes for signs of such new physics, as Domi explains. These tiny particles rarely interact with matter, allowing them to travel enormous distances, even through the Earth. They also have a remarkable property: they can change from one type, or "flavor," to another as they travel, a phenomenon known as neutrino oscillation.
The probability of these transformations can be predicted with great precision. If the observed behavior differs from these predictions, it could be a sign of new physics, potentially including a violation of Lorentz invariance. To look for such deviations, the researchers analyzed 1.4 years of data collected with the first six detection units of KM3NeT/ORCA, comparing the observed neutrino energies and arrival directions with theoretical predictions.
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