No — neutrinos cannot travel faster than light. Every reliable measurement shows them travelling at or just below light speed. They have a tiny but non-zero rest mass, which means they cannot reach exactly c, but the difference is unmeasurably small for any practical purpose.
The question keeps coming up because of a famous false alarm in 2011 — the OPERA experiment’s superluminal claim, which turned out to be a wiring fault.
The 2011 OPERA episode
In September 2011, the OPERA collaboration at Italy’s Gran Sasso laboratory announced that muon neutrinos from CERN had arrived about 60 nanoseconds earlier than light would have over the 732 km baseline. That implied a speed slightly above c.
Within hours, the announcement was the biggest physics story of the decade. Within months, it was over. An internal review found two timing problems:
- A loose fibre-optic cable between the GPS receiver and the master clock added about 74 ns of unaccounted delay.
- A separate oscillator drift subtracted about 14 ns.
Once both were corrected, the measured arrival time matched the speed of light exactly. OPERA itself published the retraction in February 2012. The episode is now a textbook case of how the scientific process catches and corrects high-profile errors fast.
How the speed limit was confirmed
Several independent measurements put very tight upper bounds on how much (if at all) neutrinos can exceed light speed:
SN 1987A is the cleanest test. The neutrino burst from that supernova arrived at Earth within about three hours of the optical signal, despite travelling 168,000 light-years. The constraint:
$$\frac{v - c}{c} < 2 \times 10^{-9}$$
That’s six orders of magnitude tighter than OPERA’s claim ever could have been.
Accelerator measurements at MINOS, T2K, ICARUS, and Borexino all measured time-of-flight for neutrino beams over hundreds of kilometres. Every one of them found neutrino speeds consistent with light speed to within a few nanoseconds per millisecond — confirming OPERA’s corrected result and ruling out the original superluminal claim independently.
Why a tiny mass keeps neutrinos below light speed
Neutrinos have non-zero rest mass. KATRIN currently limits the effective electron-neutrino mass to under 0.45 eV. Cosmological measurements suggest the sum of all three neutrino masses is below about 0.1 eV.
In special relativity, any particle with rest mass — no matter how small — travels below the speed of light. The energy needed to accelerate it to the speed of light is infinite. So neutrinos can get extremely close to c but never reach it.
For a neutrino with mass 0.1 eV at a GeV energy (typical of accelerator beams), the velocity is:
$$v/c = 1 - 5 \times 10^{-21}$$
In other words: indistinguishable from light speed for any practical experiment. Even SN 1987A’s three-hour timing margin over 168,000 light-years was only enough to test agreement to one part in 10⁹.
What if a future experiment did see superluminal neutrinos?
It would overturn special relativity, and with it most of modern physics. The current confidence that neutrinos respect the light-speed limit comes from:
- Multiple independent direct measurements (SN 1987A, OPERA-corrected, MINOS, T2K).
- The theoretical framework of special relativity passing every test since 1905.
- The Cohen-Glashow argument: superluminal neutrinos would emit electron-positron pairs as bremsstrahlung-like radiation, rapidly losing energy. We don’t see this.
The combined weight of evidence is overwhelming. Future precision measurements may tighten the bound on neutrino mass, but they will not find superluminal speeds.
The short answer
Neutrinos travel at very close to but slightly below the speed of light. Their tiny non-zero mass enforces that limit. The 2011 OPERA superluminal result was a measurement error. SN 1987A’s 168,000-light-year baseline confirmed light-speed travel to 9-decimal precision. Special relativity remains intact.
For the full OPERA story, see Anomalies and Mysteries — Part 5. For what neutrinos are in the first place, see What is a neutrino, anyway?.
Frequently asked
Can neutrinos travel faster than light?
No. Every reliable measurement of neutrino speed is consistent with the speed of light to within experimental precision. Neutrinos have a tiny but non-zero rest mass, which means they travel just below the speed of light — by an amount far too small to measure directly.
What about the 2011 OPERA result?
It was wrong. The OPERA collaboration at Gran Sasso initially announced that neutrinos from CERN arrived about 60 nanoseconds earlier than light would have. Six months of investigation traced the discrepancy to a loose fibre-optic cable in the GPS timing system (adding 74 ns of unaccounted delay) and a clock oscillator drift (subtracting 14 ns). The corrected measurement matched light speed exactly.
How was the speed limit confirmed?
Most precisely by SN 1987A. The neutrinos and photons from that supernova arrived at Earth within three hours of each other, despite travelling 168,000 light-years. That puts the upper bound on (v−c)/c at about 2 × 10⁻⁹ — six orders of magnitude tighter than the OPERA claim. Modern accelerator measurements at MINOS, T2K, and ICARUS all agree.
Why can't neutrinos go faster than light if they have such tiny mass?
Special relativity caps any particle with rest mass below the speed of light, no matter how small the mass. The energy required to push a massive particle to c is infinite. Neutrinos with masses below 0.45 eV (KATRIN's current limit) travelling at GeV energies are at v/c ≈ 1 − 10⁻¹⁸ — effectively but never quite at light speed.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2025, July 5). Can neutrinos travel faster than light?. Neutrino Times. https://neutrino-times.com/articles/can-neutrinos-travel-faster-than-light/
Chicago
Neutrino Times Editorial Team. "Can neutrinos travel faster than light?." Neutrino Times, July 5, 2025. https://neutrino-times.com/articles/can-neutrinos-travel-faster-than-light/.
MLA
Neutrino Times Editorial Team. "Can neutrinos travel faster than light?." Neutrino Times, 5 Jul. 2025, https://neutrino-times.com/articles/can-neutrinos-travel-faster-than-light/.
BibTeX
@misc{neutrino-times-can-neutrinos-travel-faster-than-light,
author = {Neutrino Times Editorial Team},
title = {Can neutrinos travel faster than light?},
howpublished = {Neutrino Times},
year = {2025},
month = {jul},
url = {https://neutrino-times.com/articles/can-neutrinos-travel-faster-than-light/},
note = {Accessed: 2025-07-05}
} RIS
TY - GEN TI - Can neutrinos travel faster than light? AU - Neutrino Times Editorial Team PY - 2025 DA - 2025-07-05 PB - Neutrino Times UR - https://neutrino-times.com/articles/can-neutrinos-travel-faster-than-light/ ER -