Neutrinos Obey The Speed Limit, After All


Neutrinos have been cleared of allegations of speeding, according to an announcement issued today by CERN and the ICARUS experiment at Italy’s Gran Sasso National Laboratory. Turns out they travel exactly as fast as they should, and not a nanosecond more.

The initial announcement in September 2011 from the OPERA experiment noted a discrepancy in the measured speed of neutrinos traveling in a beam sent to the detectors at Gran Sasso from CERN in Geneva. If their measurements were correct, it would have meant that the neutrinos had arrived 60 nanoseconds faster than the speed of light allows. This, understandably, set the world of physics a bit on edge as it would effectually crumble the foundations of the Standard Model of physics.

As other facilities set out to duplicate the results, further investigations by the OPERA team indicated that the speed anomaly may have been the result of bad fiberoptic wiring between the detectors and the GPS computers, although this was never officially confirmed to be the exact cause.

Now, a a statement from CERN reports the results of the ICARUS experiment — Imaging Cosmic and Rare Underground Signals — which is stationed at the same facilities as OPERA. The ICARUS data, in measuring neutrinos from last year’s beams, show no speed anomaly — further evidence that OPERA’s measurement was very likely a result of error.

The full release states:


The ICARUS experiment at the Italian Gran Sasso laboratory has today reported a new measurement of the time of flight of neutrinos from CERN to Gran Sasso. The ICARUS measurement, using last year’s short pulsed beam from CERN, indicates that the neutrinos do not exceed the speed of light on their journey between the two laboratories. This is at odds with the initial measurement reported by OPERA last September.

What neutrinos look like to ICARUS. (LNGS)

“The evidence is beginning to point towards the OPERA result being an artefact of the measurement,” said CERN Research Director Sergio Bertolucci, “but it’s important to be rigorous, and the Gran Sasso experiments, BOREXINO, ICARUS, LVD and OPERA will be making new measurements with pulsed beams from CERN in May to give us the final verdict. In addition, cross-checks are underway at Gran Sasso to compare the timings of cosmic ray particles between the two experiments, OPERA and LVD. Whatever the result, the OPERA experiment has behaved with perfect scientific integrity in opening their measurement to broad scrutiny, and inviting independent measurements. This is how science works.” 

The ICARUS experiment has independent timing from OPERA and measured seven neutrinos in the beam from CERN last year. These all arrived in a time consistent with the speed of light.

“The ICARUS experiment has provided an important cross check of the anomalous result reports from OPERA last year,” said Carlo Rubbia, Nobel Prize winner and spokesperson of the ICARUS experiment. “ICARUS measures the neutrino’s velocity to be no faster than the speed of light. These are difficult and sensitive measurements to make and they underline the importance of the scientific process. The ICARUS Liquid Argon Time Projection Chamber is a novel detector which allows an accurate reconstruction of the neutrino interactions comparable with the old bubble chambers with fully electronics acquisition systems. The fast associated scintillation pulse provides the precise  timing of each event, and has been exploited for the neutrino time-of-flight measurement. This technique is now recognized world wide as the most appropriate for future large volume neutrino detectors”.


An important note is that, although further research points more and more to neutrinos behaving as expected, the OPERA team had proceeded in a scientific manner right up to and including the announcement of their findings.

“Whatever the result, the OPERA experiment has behaved with perfect scientific integrity in opening their measurement to broad scrutiny, and inviting independent measurements,” the ICARUS team reported. “This is how science works.”

See more news from CERN here.

26 Replies to “Neutrinos Obey The Speed Limit, After All”

  1. Imagine the speeding ticket that could have been handed out!! Plus charges for violating the laws of physics and reckless endangerment of Einstein’s theories. I guess the neutrinos had good lawyers. If I was a photon, I would sue the press for libel, given the popular press’ poor coverage of this science story.

  2. This kerfuffle settled out about the way I thought it would.

    BTW, for some reason the side display of recent posts have not been showing up. I don’t know if this is my system problem or a decision by UT>


  3. oooh sure, with the speed police out checking for speeding neutrinos, ofc the neutrinos will slow down to below the speed-limit 😛

  4. I wrote a comments on 10 th October, 2011, that the velocity of neutrino can not faster than a photon with reason. If happen like this, Complete Unified Theory will in false position. This theory is a single theory which is applicable from particle to the Universe.

    1. There is no such theory around what I know of. People are looking for “unified theories”, but no interesting theory has come out of it as of yet. String theory may unify quantum mechanics with gravity & cosmology, but it is early days – it is valid on testing for black hole entropy et cetera, it plays nice with some cosmologies such as environmental selection in inflation, but it hasn’t predicted anything new.

      1. He is not refering to scientific theories, just his own personal mumbo-jumbo theory.

      2. Unbelievable! There’s no need to jump in and be rude like that. How do you know about it? Does it make you feel better about your theory?? I think string theory is mumbo-jumbo, but I certainly wouldn’t say that to someone like Ed Witten… I wish you all the very best, Nirmalendu Das!

      3. How do i know he is referring to his personal theory?

        Because he has already said so in previous posts, that was moderated(content edited out by moderator) for promoting personal theory.

        And have you read the nonsense his theory is about? Until you have, dont you dare come here talking about rudeness! This is a science site, not a site for idiots to promote personal delusions.

      4. So are you saying that if you think someone else is wrong then rudeness doesn’t apply?! Whatever man! Don’t try to do the moderator’s job.

      5. No, i am saying that ‘breaching the posting criteria on this site’ is wrong, and that whining about someone pointing this out, like you do here, is rude.

        I think it is time for you to look into the mirror man!

      6. Did you make this posting alias just to come here and point all this out?

        You are sad, man…

  5. The odds were overwhelming from the first day that this would prove to be a measurement error. There are too many studies that have already established that neutrinos are not super-luminal.

  6. “Whatever the result, the OPERA experiment has behaved with perfect scientific integrity in opening their measurement to broad scrutiny, and inviting independent measurements,” the ICARUS team reported. “This is how science works.”

    And they should be commended for doing what was right. Sad that not all branches of science have integrity.

    1. Speaking of integrity, we note that you don’t leave references.

      Yes, there is stuff like pathological science cold fusion and crackpot ‘science’ “Electric Universe” that try to portray themselves as scrutinized, independently verified, et cetera, when they are not. But those are not mainstream science, anyone should be able to tell the difference.

      Integrity in science is enforced by the market of ideas. It is, like all things moral, relative to the culture spawning it.

      1. What references would you like? I quoted the article and commended the OPERA group. I also expressed a wish that all branches of science follow their example of openness and inviting others to confirm or falsify their results. My opinion of course, but I would hope that most would feel the same. Do you not agree?

      2. The Dr. Kaku’s Universe blog on BigThink has had its comments section turned from legitimate discussion of physics to a cesspool of personal theories and “The Electric Universe” cr*p science. It depresses me to see how science is being denigrated in this way.

  7. A neutrino walks into a bar.

    – Sorry, the photons went through all our beer waiting for you, said the bartender.

  8. One question….I’m no physics expert, but from the stuff I’ve seen an read…..where’s the graviton ? So far the carrier particle of gravity hasn’t been found, if it exists at all..

    1. The coupling constant for the gravity field is G/c^4, which is very small. To get a graviton signal requires enormous energy, far beyond LHC energy.


      1. Thanks….so we would need a Super LHC in order to detect a graviton ? This has been bugging me….Please correct me If I’m wrong but I think that the next step after the Higgs Bosson would be detecting it ? or something else. Also, do we need the graviton to complete the standard model ?

Comments are closed.