A bizarre high-energy particle detected in February 2023 originated from a primordial black hole hiding inside a fifth dimension, according to a radical cosmological theory attempting to explain the neutrino that slammed into Earth with tens of thousands of times more power than a particle accelerator can produce.
The Cubic Kilometer Neutrino Telescope (KM3NeT) detector positioned off the coast of Sicily recorded an impossible signal in early 2023. The bizarre neutrino carried roughly 35 times more energy than any neutrino observed previously, registering at an intensity about 30,000 times higher than the capabilities of CERN’s Large Hadron Collider. Astrophysicists immediately began searching for its source, considering ordinary astrophysical suspects like blazars alongside far more exotic possibilities.
Proposing a Fifth Dimension
A paper published in Physical Review D proposes that the event stems from a microscopic primordial black hole formed from light-years-long cracks in spacetime called cosmic strings. According to the research team, these ancient objects would have been cloaked inside a hypothetical fifth dimension often discussed in string theory.
The reason we do not see it is that we live on a one-plus-three-dimensional brane, on which all other interactions—like electromagnetism—take place. The only force which can penetrate the fifth dimension is gravity.
Dieter Lüst, Max Planck Institute for Physics
Evaporating primordial black holes would leak neutrinos into our observable universe while keeping photons trapped because gravity rules over this extra dimension—which can span as tiny as a thousandth of a millimeter.
Comparing Antarctic Detector Silence
The IceCube Neutrino Observatory in Antarctica, featuring a mesh of detectors spanning an area roughly 20 times larger than KM3NeT and operating for more than a decade since 2011, recorded nothing from the event. This silence remains one of the most confounding aspects of the KM3NeT detection.
It was really surprising because [KM3NeT’s event] was so much higher in energy than IceCube had ever seen,
Erin O’Sullivan, neutrino astrophysicist at Uppsala University in Sweden and spokesperson for IceCube
Physicists Debate Theoretical Weight of Fifth Dimension Model
Cosmologists point out that the existence of a fifth dimension remains unverified, and hanging an entire cosmic origin story on a single neutrino requires a substantial leap. Independent physicists have expressed caution given the sheer theoretical weight of the proposal.
Massachusetts Institute of Technology physicist David Kaiser observed that the model still looks beautifully consistent,
while Andrea Thamm of the University of Massachusetts Amherst noted that the framework offers very nice explanations for several things that we have evidence for,
though other researchers who have studied primordial black holes find the mechanics intriguing.
Which doesn’t mean it’s right. But it is using some really off-the-shelf, more typical elements that are woven into many parts of our understanding of black hole physics.
David Kaiser, Massachusetts Institute of Technology
Until future observations confirm the source, the mystery of the 2023 signal persists. Cosmic rays colliding with gas or radiation routinely produce neutrinos, meaning the particle does not necessarily require an exotic origin, as other scientists emphasize that standard explanations remain fully on the table.
Which doesn’t mean it’s right. But it is using some really off-the-shelf, more typical elements that are woven into many parts of our understanding of black hole physics.
David Kaiser, Massachusetts Institute of Technology
