Scientists are testing whether one of Einstein’s most fundamental principles holds true throughout the Universe.
A neutrino telescope deep in the Mediterranean Sea has put one of Einstein’s fundamental principles to a new test. After analyzing 5,828 atmospheric neutrino candidate events, scientists found no evidence that Lorentz invariance, a cornerstone of relativity, had been violated. Their findings place new restrictions on theories suggesting that the laws of physics might behave differently under certain conditions.
The international KM3NeT collaboration conducted the study using KM3NeT/ORCA, an underwater detector designed to investigate neutrinos and their unusual behavior. Published in the Journal of Cosmology and Astroparticle Physics (JCAP), the research establishes the first direct experimental limits on certain possible violations involving muon and tau neutrinos, two types of these elusive particles.
Could Spacetime Have a Hidden Structure?
Lorentz invariance requires the fundamental laws of physics to remain unchanged for observers moving at different constant velocities or facing different directions. Some theories of quantum gravity, which attempt to unite general relativity with quantum physics, suggest that this principle might not hold perfectly at extremely small scales.
One possibility is that spacetime is not truly continuous but consists of tiny, discrete units. If such a structure exists, it could produce subtle deviations from the predictions of relativity.
“We still don’t know whether our spacetime is continuous or might be discrete,” explains Alba Domi, a researcher at the Erlangen Center for Astroparticle Physics (ECAP), Friedrich-Alexander-Universität Erlangen-Nürnberg, and one of the study’s corresponding authors. “Looking for violations of Lorentz invariance is one way to investigate this possibility.”
Why Neutrinos Are Ideal for Testing Einstein’s Physics
Neutrinos are exceptionally difficult to detect because they interact so weakly with matter. Vast numbers pass through Earth without leaving a trace, allowing them to travel enormous distances with little interference.
These particles also possess an unusual ability: they can transform between different types, or “flavor” (this is the term used by scientists), as they travel. Known as neutrino oscillation, this phenomenon follows mathematical predictions that scientists can test against observations. Unexpected changes in these oscillations could indicate previously unknown physical effects, including violations of Lorentz invariance.
To search for such discrepancies, the researchers examined 1.4 years of observations collected by KM3NeT/ORCA. At the time, the telescope was operating with only six detection units. The team compared the neutrinos’ measured energies and arrival directions with theoretical predictions to identify potential departures from established physics.
Underwater Observations Set New Limits on Physics
The analysis revealed no evidence of Lorentz invariance violation. However, it established tighter constraints on certain possible effects, including those that could influence oscillations between muon and tau neutrinos.
Despite relying on an early version of the detector, the results were competitive with measurements from established experiments such as IceCube and Super-Kamiokande, which have collected neutrino data over much longer periods.
“These results show the potential of KM3NeT/ORCA to test fundamental principles of physics, even with a relatively small detector,” says Lukas Hennig, a PhD student at ECAP and the study’s other corresponding author. “With more data and an expanding detector, we will be able to search for even smaller effects.”
The Next Frontier: Neutrinos From Deep Space
As KM3NeT/ORCA expands toward its full planned configuration, researchers expect to improve their sensitivity to possible deviations from relativity. They also hope to extend these investigations to KM3NeT/ARCA, a detector designed to study much higher-energy neutrinos originating from distant astrophysical sources.
Some proposed violations of Lorentz invariance could become more pronounced as neutrino energy increases or as particles travel across greater distances. Neutrinos arriving from distant cosmic sources may therefore offer a way to test effects too small to detect with atmospheric neutrinos.
“ARCA could be particularly well suited to this kind of research, but we don’t yet have enough astrophysical neutrino events to perform such an analysis,” explains Domi.
Reference: “Atmospheric neutrino constraints on Lorentz invariance violation with the first six detection units of KM3NeT/ORCA” by O. Adriani et al., 4 November 2026, Journal of Cosmology and Astroparticle Physics.
DOI: 10.1088/1475-7516/2026/11/012
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