A single ultra-high energy particle detected deep under the sea may have been traveling through space since the dawn of time.
April 23, 2026
Original Paper
The KM3NeT event: a primordial high energy neutrino?
arXiv · 2604.18677
The Takeaway
The KM3NeT detector recently caught a neutrino with such extreme energy that it likely dates back to the very beginning of the universe. These primordial relics were created just moments after the Big Bang and have been flying through the vacuum ever since. If this particle is indeed a relic, it carries direct information about the state of the universe before stars even existed. Detecting more of these events could allow scientists to map the first light of the cosmos in a way light alone cannot. It transforms a single subatomic collision into a telescope looking back billions of years.
From the abstract
High energy neutrinos can be injected in the early Universe from the decay or annihilation of long lived primordial relics. We analyse the possibility that the ultrahigh energy neutrino event recently observed by the KM3NeT neutrino telescope could have such an origin. This possibility has the advantage of leading to a sharp spectral feature in a way that the neutrino flux can be small at all energies except at the KM3NeT event energy. Thus, along this scenario the tension with null results from