Neutrinos and Cables

By Sean Carroll | February 22, 2012 1:16 pm

I’m a little torn about this: the Twitter machine and other social mediums have blown up about this story at Science Express, which claims that the faster-than-light neutrino result from the OPERA collaboration has been explained as a simple glitch:

According to sources familiar with the experiment, the 60 nanoseconds discrepancy appears to come from a bad connection between a fiber optic cable that connects to the GPS receiver used to correct the timing of the neutrinos’ flight and an electronic card in a computer. After tightening the connection and then measuring the time it takes data to travel the length of the fiber, researchers found that the data arrive 60 nanoseconds earlier than assumed. Since this time is subtracted from the overall time of flight, it appears to explain the early arrival of the neutrinos. New data, however, will be needed to confirm this hypothesis.

I suppose it’s possible. But man, that would make the experimenters look really bad. And the sourcing in the article is just about as weak as it could be: “according to sources familiar with the experiment” is as far as it goes. (What is this, politics?)

So it’s my duty to pass it along, but I would tend to reserve judgment until a better-sourced account comes along. Not that there’s much chance that neutrinos are actually moving faster than light; that was always one of the less-likely explanations for the result. But this isn’t how we usually learn about experimental goofs.

Update from Sid in the comments: here’s a slightly-better-sourced story.

Update again: and here is the official CERN press release. Not exactly admitting that a loose cable is at the heart of everything, or even that the result was wrong, but saying that there were problems that could potentially invalidate the result.

  • Sid

    The CBC story is better sourced though the CERN spokesman mentioned at the end only says that “a flaw in the GPS system has been found” and doesn’t go into details.

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  • Bob F.

    Well, it was fun while it lasted. And the next time someone that I’m giving tech support to tells me I’m being silly when I ask them if they checked their cables……………………..

  • Thomas Larsson

    Of course, everyone knew that there had to be some glitch somewhere. If it is too strange to be true, it is not true. Sort of reminds me of the 17 keV neutrino.

  • Sesh

    Only ~230 citations for the original paper.

  • Carl Brannen

    It’s going to be really really tough to get a 60ns delay out of a bad fiber optic connection. They either work or they have high error rates. Assuming 100M bits per second cable (i.e. 125MHz), that’s a lot of bits to store away somewhere.

  • Sam

    Indeed if this is true, that it was all due to a faulty cable, then what a HUGE embarrassment it will be to the whole OPERA team. And they will have no-one to blame but themselves, since they put out a press-release on this result in the first place.

  • EB

    The official statement from the collaboration:

    “The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock.

    These two issues can modify the neutrino time of flight in opposite directions.”

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  • Albert Einstein

    Highly Technical Question: would it have been possible to check the cables BEFORE putting the paper on the arxiv? Another question: why the rush? Who were they trying to beat?

  • Low Math, Meekly Interacting

    I believe Discover Magazine made FTL neutrinos its #1 Science Story of 2011.

    This one will make a lot of people look bad.

  • In Hell’s Kitchen (NYC)

    “But man, that would make the experimenters look really bad.”

    what would it make the theorists (who deluged us with so much garbage) look like ?

  • Low Math, Meekly Interacting

    Don’t worry, #12, extra dimensions will be just fine.

  • marshall

    60 nanoseconds is a huge cable error, equivalent to about 10 meters of cable. It is possible that there was some internal reflection in the loose cable which caused such a big error, but I suspect that the real problem was the system latched onto the trailing edge of the 1 pps timing signal – this is more likely to happen when something (like a bad cable) is screwing up the timing pulse, and it can cause a considerable excess delay (order 100 nanoseconds or more). In many systems the width of the 1 pps pulse is not controlled, and so it will vary. This leads to the common symptom of this problem – the timing becomes erratic at the nanosecond level. If such timing is used in VLBI (for example) then the extra noise is pretty noticeable.

    If something like this was the cause of their error then they deserve the bad PR they will get, as they really should have included a timing professional as part of the experiment (as opposed to a consultant role). I have had several discussions with timing professionals about the superluminal neutrino results, and each time the trailing edge issue has come up.

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  • Navneeth

    Caren Hagner, a member of OPERA at the University of Hamburg in Germany, says “For the moment the collaboration decided not to make a quantitative statement, because we have to recheck and discuss the findings more thoroughly.”

    If only they had done this the first time ’round… .

  • David Brown

    According to Carl Brannen, “It’s going to be really really tough to get a 60 ns delay out of a bad fiber optic connection.” There are 3 basic possibilities for explaining the OPERA neutrino anomaly:
    1. There are one or more serious experimental errors.
    2. Neutrinos are travelling faster than the speed of light in a vacuum.
    3. Photons are travelling slower than general relativity theory predicts.
    I call the Rañada-Milgrom apparent-or-real effect the apparent or real necessity of replacing the -1/2 in Einstein’s field equations by -1/2 + sqrt((60±10)/4) * 10**-5. “The Pioneer anomaly as acceleration of the clocks”
    The OPERA neutrino anomaly confirms the Rañada-Milgrom effect. The flyby anomalies, NASA’s Gravity Probe B, and the Sachs-Wolfe effect also confirm the Rañada-Milgrom effect. The empirical evidence shows that general relativity theory is slightly wrong.

  • Eli Rabett

    You ever actually do an experiment Sean? Bad cables are common, optical fibers merely allow new failure modes. New experiments often introduce new failure modes.

  • marshall

    In Hell’s Kitchen (NYC) Says:

    “But man, that would make the experimenters look really bad.”
    what would it make the theorists (who deluged us with so much garbage) look like ?

    Like theorists. That’s what they do, try and make sense of new experimental results, and there is nothing wrong with it, even if those results later turn up short.

  • anon

    Really, did anyone actually expect this anomaly to turn out differently?

    There are hundred of ways that OPERA could have got this wrong, and almost all of them are embarassing. The odds were always high that this was a trivial mistake.

  • Gizelle Janine

    Holy shit. You make a valid point on how these people look.

    Well, there goes one day I thought I wasnt wasting. Sean, you insipire rage out of me. :D

  • Joel Rice

    Why is it any worse than bad connections for magnets at the LHC or a bad mirror on the Hubble telescope, or crashing a spacecraft because somebody didnt convert inches to centimeters ? Heck – a long time ago a new release of unix broke my rs232 code. Oh well – the wonders of technology.

  • Tony Mach

    @Carl Brannen
    “It’s going to be really really tough to get a 60ns delay out of a bad fiber optic connection.”

    Don’t assume it is ATM, Ethernet or the such. It might simply be a “home-made” connection to transmit information via a fiber optic cable and a simple pulse of light.

    A loose cable could attenuate the signal. Then a non-linear rise of the signal in the transmitter (and we are talking about real life transmitters, not a theorized ideal source), combined with the threshold of the receiver => Delayed signal.

    In that case, they should have you used a pulse and sampled both flanks…

    @David Brown
    What the heck are you talking about?

  • Karsus

    Joel is right.

    Shit can happen when leave the couch you make your hands dirty.

  • Sean Carroll

    Just to make one thing clear: it doesn’t make the experimenters look bad to find a loose cable. Experiments are hard, and tiny glitches like this happen all the time.

    What makes them look bad is announcing that neutrinos move faster than the speed of light without having checked things like this. Before you have a paper and a press conference for something like that, it’s your job (especially when nobody is directly competing with you) to do absolutely everything to make sure you haven’t made such a mistake. If that includes tearing every piece of apparatus apart and building it from scratch, so be it. Sure, you can throw it out to the community and ask people to check you, but for a result this big you first have to do everything in your power to check yourself.

  • Eric Shumard

    OPERA uses an 8 km single-mode fiber optic cable that goes from the GPS receiver on the surface to the underground detector. OPERA reports that the delay of this cable is 40993.4 ns. Assuming this is the fiber cable in question, it is conceivable that they measured this delay before installation and then the delay changed due to the installation configuration being different than the measurement configuration, e.g., the cable is was curled up during measurement but not after installation. Bending a fiber optic cable can change the dispersion of the signal and induce signal loss. This seems more plausible than a bad connection resulting in a significant delay but is still speculation.

  • Phil

    I agree with David Brown. In light of this discovery, the left side of Einstein’s Equations should be changed from:

    R_{munu} – (1/2)Rg_{munu}


    R_{munu} – (1/2 + sqrt((60±10)/4) * 10**-5)Rg_{munu}

    It follows from experiment! Rañada and Milgrom deserve next year’s Nobel Prize. Time to rewrite the GR textbooks!

  • David Brown

    @Tony Mach: By looking at several forms of empirical evidence, I arrive at the hypothesis that the basic problem is that the OPERA team failed to consider the effect of dark matter (or its Milgrom-equivalent). The dark matter (or its Milgrom-equivalent) causes a GPS timing problem. You might say that dark matter causes time to slow down more than standard general relativity theory predicts.
    On pages 83 and 84 of Einstein’s “The Meaning of Relativity”, there are 3 fundamental conditions for the components of Einstein’s tensor of the gravitational potential. The first condition is the tensor must contain no differential coefficients of the Fundamental Tensor components of greater than second degree. The second condition is that the tensor must be linear in these Fundamental Tensor components of second degree or less. The third condition is that the divergence of the tensor must vanish identically. The first two conditions are necessary to derive Newton’s theory of the gravitational potential in the non-relativistic limit. The third condition is necessary to eliminate energy gains or losses from alternate universes. But does dark matter consist of gravitational energy that seems to derive from alternate universes? Consider the following:
    Two Button Hypothesis of General Relativity Theory: In terms of quantum gravitational theory, Einstein’s general relativity theory (GRT) is like a machine with two buttons: the “dark energy” button and the “dark matter” button. The dark energy button is off when the cosmological constant is zero and on when the cosmological constant is nonzero. The dark matter button is off when -1/2 indicates the mass-energy divergence is zero and on when -1/2 + sqrt((60±10)/4) * 10**-5 indicates the mass-energy divergence is nonzero.

  • In Hell’s Kitchen (NYC)

    marshal sez: Like theorists. That’s what they do, try and make sense of new experimental results, and there is nothing wrong with it, even if those results later turn up short.

    I hope you really meant to write “Like SOME theorists.”

  • Gene

    #12 LMMI: exactly! Both Discover and Scientific American contributed to marketing a cable failure as one of the biggest science stories of the year, amazing and shameful.

  • Phil

    @ David Brown, #30,

    You are totally making sense. I see it! I completely agree with you. Have you published a paper on these results yet? I want to learn more! You are on to something big here!

  • Ted Danson

    re. David Brown

    You have to realize that people see posts like yours and just see noise. Here is what you should do instead:

    * Learn in detail the theories that you’re looking to improve.

    * Show carefully and clearly why your model improves upon current mainstream models. If you truly want to succeed, it is important that you do this in a way that is sympathetic to the way physics is normally done, how physicists usually see research. i.e. Do not use blog comment sections to talk about your the details of your ideas. It never ever works! Distribute you work via papers, and only use LaTeX. If you have initial trouble putting papers on the arxiv then use or something.
    If you do not get this stage right then there’s a serious danger of torpedoing your own aims.

    It is my experience that *very few* people in your position actually make the effort to do these things. I could probably count the number on my hand. It makes all the difference. Good luck!

    re. Phil, for sarcasm to be done well, it has to be done with some precision.

  • Phil

    Yes, David Brown, and might I add one more piece of advice:

    Call 1/2 + sqrt((60±10)/4) * 10**-5 a name, like “Brown’s number”, and give it a symbol, such as B, for Brown. Then, your equation reduces to the neater, and more serious-looking:

    R_{munu} – BRg_{munu} = 8*Pi*T_{munu}

  • Carl Brannen

    @Tony Mach; I agree completely, it would have to be a home-made connection; commercial interfaces are DC-balanced and so are immune to having changes in attenuation appear as an apparent change in propagation delay. But for this to explain the problem, they’d have to be working with rise times on the order of 60ns. For people sophisticated enough to use 8km single mode fiber, that’s hard to believe.

    An explanation I would believe (and a sign of miserable engineering) would be to leave the cable dark for 1/2 second and then on for 1/2 second. Then you could have some severe delays because (my guess is that) fiber amplifiers are almost always capacitively coupled. As far as evidence for this, Specracom’s 1PPS GPS synchronization output is 5V TTL; a natural thing (ooooops) would be to hook this up to the fiber through a TTL to fiber converter (the type that is just a straight buffer): Spectracom’s data is here:

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  • David Brown

    @Ted Danson: A study of the difficulties that Milgrom encountered in publishing his work indicates that someone else will be gain priority in publishing the Rañada-Milgrom effect in a refereed journal.
    “I think few people appreciate that the main difficulty for DM is that the host of regularities pointed out by MOND, if taken as just a summary of how DM behaves and interacts with normal matter, suggests that these two matter components are coupled and correlated very strongly in many ways. … if MOND does turn out to have some truth to it, the fact that it has encountered so much opposition will just show how nontrivial a thought it was.” — Mordehai Milgrom, interview entitled “Dark-matter heretic”, American Scientist, Jan.-Feb. 2003, Vol. 91, #1, p. 1
    Consider the following argument:
    Premise 1. There is overwhelming empirical evidence in favor of Milgrom’s non-relativistic MOND, according to the work of Milgrom, McGaugh, and Kroupa.
    Premise 2. For low gravitational accelerations, non-relativistic MOND is approximately equivalent to the Rañada-Milgrom effect, because the approximate equivalence is easily shown by a scaling argument.
    Premise 3. The approximate value of the dark-matter-compensation-constant is given by the Pioneer anomaly, and this value is approximately confirmed by the OPERA neutrino anomaly.
    Conclusion. The Rañada-Milgrom effect is approximately valid, at least for low gravitational accelerations and non-relativistic velocities.
    Is Milgrom’s non-relativistic MOND incorrect? Is Einstein’s general relavity theory 100% correct? Is the Lambda CDM model (LCDM) 100% correct?
    I quote Prof. Dr. Pavel Kroupa from a (Nov. 1, 2011) e-mail,
    “My criticism is not based on me not liking dark matter, but is a result of rigorous hypothesis testing such that, from a strictly logical and scientific point of view, LCDM is definitely not a viable model of cosmological reality. I do not write such statements because I do not like LCDM and its ingredients, but because every test I have been involved with falsifies LCDM. At the same time, the tests of MOND we performed were done on the same footing as the LCDM tests. The MOND tests yield consistency so far. I am not more “fond” of MOND or any other alternative, but the scientific evidence and the logical conclusions cannot be avoided. And it is true, I must concede, that MOND has an inherent beauty which must be pointing at a deeper description of space time and possibly associated quantum mechanical effects which we do not yet understand (compare with Kepler laws and the later Newtonian dynamics).”

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  • Ted Danson

    @ David Brown:

    ‘@Ted Danson: A study of the difficulties that Milgrom encountered in publishing his work indicates that someone else will be gain priority in publishing the Rañada-Milgrom effect in a refereed journal.’

    If you’re worried about getting credit for having the idea first, I assure you that it would be sufficient to put your work on a non-peer reviewed website such as Stop being so lazy.

  • Low Math, Meekly Interacting

    #22: Apparently, some people did. What’s bizarre is that it took approximately a week for grounded theorists to publish a couple devastatingly fatal critiques of the notion of FTL neutrinos, as if the approx. 100 gagillion data points confirming SR weren’t enough. But somehow the “hey, it could happen” notion lived on because, hey, neutrinos of some energy that we hadn’t yet gotten around to clocking (because it would be pretty low priority kind of investigation) just might take a shortcut through extra dimensions. I mean, hey, you never know, right? And that’s the beauty of such extensions of reality: You really never know!

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  • Neil

    Come on, Sean. The experimenters make a bone-head mistake, or relativity is wrong. Which is more likely?

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  • marshall

    Interview, in German, with an Opera scientist about the problem :

    Translation (in the first comment) :

    The crucial bit :

    We do not know how crooked the plug actually was at the time of our measurements last year. Sub-sequentially we do not know the actual time delay.

    So, they just don’t know whether the neutrinos were superluminal, subluminal, or what.

    I still think they were synced on the trailing edge of the timing pulse.

  • Douglas Watts

    An informed source says a bad cable to Paul’s Hofner left-handed bass is what really broke up the Beatles.

    Check your cables !!!

  • Eli Rabett

    @ Sean C; If that includes tearing every piece of apparatus apart and building it from scratch, so be it.

    Sure way to introduce new errors.

  • Avram Davidson

    Time barrier was broken in 1979. The N.S.A. knows all about it.

  • RedGreenBlue

    A word-choice note: It should be “social media,” not “social mediums.” “Mediums” is the plural of the kind of “medium” who holds a séance—or were y0u trying to get into better sync with the new Discover Magazine, the one that runs articles about bogus experimental proof of ESP?

  • David Brown

    @Ted Danson & @Phil:
    See “Anomalous Gravitational Acceleration and the OPERA Neutrino Anomaly”. What are your criticisms?

  • Steve Bergman

    I don’t think reporting on their puzzling results makes the experimenters look bad. They spent 3 years, or whatever, rechecking a very tricky and complicated experiment, looking for an answer. It’s not obvious to me how a bad fiber optic connection would result in a 60 ns delay. One would not expect delays, but protocol errors. Of course, errors and retransmissions would result in delays. And if the errors weren’t being reported or logged…
    In the absence of detailed information, I’m willing to assume due diligence. I’ve faced too many difficult to troubleshoot problems of my own to be too terribly critical.

    Anyway, despite the resulting media circus in some quarters, in others it provided an excellent opportunity for the public to see, first hand, how science works. And provides a good example of the value of healthy scientific skepticism. Those are arguably the most important aspects of the whole episode.

  • David Brown

    If I am not mistaken, then Prof. Milgrom, Prof. Antonio Fernández-Rañada, and I might be plausible candidates for the Nobel prize. In order to avoid a future big stink with the Nobel prize committee, I should put on record that Fernández-Rañada and I might be regarded as implicit collaborators in the sense that he and I have exchanged e-mails and profoundly influence each other’s thinking. He wants to be more thorough and cautious before rushing into print.
    See “Anomalous Gravitational Acceleration and the OPERA Neutrino Anomaly”.
    Is M-theory doomed to the netherworld of non-prediction if the Finite Nature Hypothesis is false?
    See “Finite Nature Hypothesis and Space Roar Profile Prediction”
    Is Milgrom the Kepler of contemporary cosmology? — D. Brown

  • Phillip Helbig

    We’ll see if he mentions you in the acknowledgements. By replying to comment #52, I am attracting attention to it, so I expect a small percentage of said prize as compensation. Account details available on request.

  • David Brown

    Phil Gibbs has blocked out the “Anomalous Gravitational Acceleration and the OPERA Neutrino Anomaly.” See for what has been blocked out.
    In my opinion, Fernández-Rañada is still mulling over the Rañada-Milgrom effect and might not want “credit” for the idea. I don’t think I was wrong in not mentioning exchange of e-mails in the original article because after all I NAMED the effect after Rañada and Milgrom and independently thought of it myself although Fernández-Rañada did first publish the basic QUALITATIVE idea but he botched the quantitative formulation. However, the fact that he didn’t automatically reject the Rañada-Milgrom effect when I mentioned it to him TOTALLY CONVINCED me that the effect is valid — before that I had doubts but after I felt sure. I need to put pressure on Fernández-Rañada to publish and then we can dispute credit for the idea if the idea is valid.

  • David Brown

    @53 Phillip Helbig, I gather that you are Phil Gibbs. If I write another article explaining the role of Prof. Fernández-Rañada in my thinking then will you either unblock the article or let me put out another article? The thought occurred to me that the Nobel prize committe might give a prize to Milgrom and me and leave out Fernández-Rañada, and the exchange of e-mails (rather minimal) might be important in assigning credit. Very soon, dozens of theoretical physicists are going to independently think of the Rañada-Milgrom effect.

  • Phillip Helbig

    No, I am not Phil Gibbs. I post under my real name. I had never heard of Phil Gibbs until today.

  • David Brown

    @56: Phillip Helbig, thank you for responding to my guess about Phil Gibbs. Apparently, Phil Gibbs read my #52 comment and blocked out my paper. It is merely a coincidence that Phillip Helbig and Phil Gibbs both are “Phil”s. Phil Gibbs runs — I believe that Prof. Fernández-Rañada will delay too long in publishing his ideas on the Rañada-Milgrom effect. My vixra article on the Rañada-Milgrom effect might be construed as 100% my own work, but there might be a good case for splitting the credit 90% for me and 10% for Fernández-Rañada. His contribution is that he is a world-class expert on general relativity theory and as soon as he implicitly indicated that the effect might be approximately correct then I became 100% convinced that the Rañada-Milgrom effect explains the Pioneer anomaly, the flyby anomalies, MOND, the Gravity Probe B results, and several other anomalies. If I am not mistaken and Milgrom and I happened to share a prize then my origini]al article on the Rañada-Milgrom effect should at least have mentioned the role of the e-mails in my thinking. My ideas on M-theory with the finite nature hypothesis might be 100% nonsense, but the evidence shows that the Rañada-Milgrom effect is approximately correct although it is extremely unclear WHY the effect is approximately correct.

  • David Brown

    Phillip Helbig, Phil Gibbs, and any physicists who are interested in gravitational theory should consider 4 ideas:
    (1) Milgrom is the Kepler of contemporary cosmology.
    (2) The work of Milgrom, McGaugh, and Kroupa confirms Milgrom’s MOND.
    (3) An easy scaling argument shows that MOND is approximately equivalent to the Rañada-Milgrom effect, at least for low gravitational accelerations.
    (4) The OPERA neutrino anomaly is NOT due to experimental error.
    See “Anomalous Gravitational Acceleration and the OPERA Neutrino Anomaly (Updated)”. My ideas on M-theory with the finite nature hypothesis might be 100% crackpot, but the Rañada-Milgrom effect is another story. As soon as physicists realize that the OPERA neutrino anomaly is for real then THERE IS GOING TO BE A GIANT STAMPEDE. Believe it or not, but you might kick yourself if the Rañada-Milgrom effect is valid and you ignore it.

  • Phillip Helbig

    You don’t mention Bob Sanders. I know him rather well from the time we were both working at the Kapteyn Institute in Groningen (Bob is still there, but retired.) I’ve certainly looked in a bit of detail, with an open mind, at MOND. However, I think your confidence is exaggerated, especially with regard to the OPERA result. All is not well with CDM, but to what extent MOND or something like it is the answer is at best unclear at the moment.

  • David Brown

    @59, Phillip Helbig: If someone would provide information on Bob Sanders (Robert H. Sanders), I would like to create a Wikipedia entry for him. Mathematical facts indicate that M-theory is correct, and M-theory and MOND seem to imply that the Rañada-Milgrom effect is THE ONLY HOPE for MOND. According to both McGaugh and Kroupa, MOND has been approximately confirmed whenever it makes testable predictions. Is M-theory doomed to the netherworld of non-prediction if the Finite Nature Hypothesis is false?
    See “Finite Nature Hypothesis and Space Roar Profile Prediction”
    Are there any comments (no matter negative) on the preceding ideas?

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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