Record-breaking neutrino is most energetic ever detected
Context and References
- Discussion centers on a 120 PeV neutrino detected by the KM3NeT undersea detector, with links to the Nature paper and popular-science coverage.
- People connect it to the earlier “Oh-My-God” ultra–high-energy cosmic ray and to explainer videos on how astrophysical accelerators (e.g., supernovae) might produce such particles.
Neutrino Properties and Interaction Lengths
- Neutrinos are extremely light (≈1/500,000 of an electron’s mass), interact only via the weak force and gravity, and pass through matter almost unhindered.
- A commonly cited rule of thumb: about a light‑year of lead would be needed to fully block a bright neutrino source.
- Estimates of interaction/mean free path at these energies vary in the thread: some say “tens of kilometers in rock,” others suggest ~100–1000 km in water/lead, noting that cross-section grows strongly with energy.
- Clarification: neutrinos do carry weak charge, which is how they are produced and detected.
Energy Scale and Analogies
- 120 PeV ≈ 0.02 J: roughly 10% of the kinetic energy of a ping‑pong ball in casual play.
- A lead researcher is quoted: during detector transit the resulting muon emitted light at ~2 horsepower, but only for microseconds.
- Comparisons emphasize that this is huge energy for a single particle but negligible in total for any practical power use.
Effects on Matter, People, and Machines
- Back-of-envelope calculations explore what a “ping‑pong ball mass” of such neutrinos would do, with estimates ranging from local radiation damage to multi‑kiloton TNT equivalents if all energy deposited—acknowledged as highly idealized.
- Realistically, only a tiny fraction of neutrinos interact; even a huge flux would mostly pass through a human or the Earth.
- Bit flips in electronics are discussed: soft errors are a known issue (especially in DRAM), but cosmic rays and local radioactivity dominate; neutrinos are not a special threat.
Detection Method and Water Detectors
- KM3NeT detects a high‑energy muon track and infers a neutrino that likely traversed large amounts of seawater/rock.
- Commenters note that no known Standard Model particle besides a neutrino could plausibly create such a muon deep in matter.
- Large water volumes are used to observe Cherenkov light from charged particles moving faster than light does in water.
Communication and Faster‑Than‑Light Speculation
- Neutrino communication is floated as a way to send signals straight through the Earth; main barrier is enormous, expensive detectors.
- Even massive neutrinos travel at (1 − ~10⁻³⁷) c at these energies, so they would still beat any signal routed around the planet’s surface.
- Earlier “faster‑than‑light neutrino” anomalies and the idea of neutrinos as tachyons are mentioned, with the consensus that only a solid positive mass‑squared measurement will decisively kill tachyon models; current hints remain within error bars.
- SN1987A is cited: neutrinos arrived before photons, usually attributed to photons being delayed in stellar ejecta, not superluminal travel.
Units, Calculators, and Numerics
- Some fun around needing high‑precision arithmetic to redo the energy/velocity algebra; people mention big‑number tools and symbolic math services.
- One participant explicitly computes the neutrino’s speed as 0.999…(36 nines)…829 c, using an assumed upper bound on neutrino mass, and others note this is only a lower bound on v.
- Side thread on SI vs cgs and why kilogram, not gram, is the SI base unit; recognized as a historical wart but preferable to non‑metric systems.