Superluminal Neutrinos are so 2011

By Sean Carroll | March 16, 2012 7:30 am

We all knew that when the OPERA experiment announced preliminary evidence that neutrinos were traveling faster than the speed of light, the result was so hard to swallow that independent confirmation from other experiments would be necessary before too many people jumped on the bandwagon. In the meantime, a number of theoretical papers pointed out difficulties in accepting the result at face value (probably the cleanest by Cohen and Glashow). And just last month OPERA itself announced that they had located a couple of possible systematic errors in their experiment, without actually backing off the original result. But lets just say things haven’t been looking good.

Now we have what might be the nail in the coffin: another experiment, ICARUS, at the same laboratory in Gran Sasso in Italy, has reported an independent measurement of the neutrino time-of-flight from CERN. (The CERN twitter feed points to an frustratingly vague press release; more useful info from Tommaso Dorigo.) Answer: spot on the speed of light. They even have a paper on the arxiv, from which we get this lovely plot:

Colloquially, we would say “game over, man.” The new measurements sit spot on the speed of light (zero on the plot), and are inconsistent with OPERA. (Actually neutrinos have tiny masses and therefore move just a bit slower than light, but it’s close enough as to be invisible in this plot.) Note that ICARUS had previously “refuted” OPERA, but in a much more indirect way, by checking that the neutrinos hadn’t lost any energy along the way. This new result is a straight-up check of the original claim, and it falls short.

As Tommaso points out, the precision of the ICARUS result is comparable to that of OPERA, so if you live in a mental space free of theoretical priors you could assign 50/50 weight to each one. Those of us in the real world should be ready to accept that the speed of light isn’t just a good idea: it’s the law.

  • scunner

    You mean systemic not systematic I believe.

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  • asad

    @ scunner #1: No, he means systematic, as it is commonly used in physics. A systematic error is one that biases the result of an experiment away from the true value, reducing the accuracy of the experiment. This is opposed to random error that simply adds noise to the measured value, reducing its precision.

  • X

    I think the truly remarkable thing here is that OPERA has created a world in which making a competent measure of the speed of light is now a publishable result and not an undergrad lab project.

  • Nick Huggett

    Can I quibble about the suggested (unintentionally, no doubt) correspondence between mass and speed: ‘Actually neutrinos have tiny masses and therefore move just a bit slower than light, but it’s close enough as to be invisible in this plot.’

    The experiment equally shows that the earth has a velocity ‘just a bit slower than light’ – in the rest frame of the neutrinos. But (comparatively) the earth doesn’t have a ‘tiny’ mass.

  • Nick Huggett

    Can I quibble about the suggested (unintentionally, no doubt) correspondence between mass and speed: ‘Actually neutrinos have tiny masses and therefore move just a bit slower than light’.

    The experiment equally shows that the earth has a velocity ‘just a bit slower than light’ – in the rest frame of the neutrinos. But (comparatively) the earth doesn’t have a ‘tiny’ mass.

  • Pingback: Ícaro vs Opera. | Pablo Della Paolera()

  • John W. Kennedy

    The point is that, because neutrinos have non-zero mass, they cannot quite achieve the speed of light. Only massless particles can do that (and they, in fact, not only can, but must).

  • Ian Liberman

    @ Nick I do not see your statement as correct. The neutrinos speed works out to be about to be very close to the speed of light (300,000km/sec),in this study, with a very small mass as stated by yourself and Sean. The gravitational pull between the Earth and Sun causes the Earth to travel around the Sun at a velocity of 29.8 km/sec. Very different and much slower than the speed of light and the huge mass of the earth would always produce a slow velocity that would not be close to the speed of light. Only massless particles would. Where in the experiment did you see that the earth has a velocity, “a little bit slower than the speed of light” ? The earth`s “rotational velocity” is approximately .47 km/sec .Also a slow speed and nowhere near the speed of light.

  • justin petitt

    What frame of reference are you referring to speed of the earth relative to?

  • Georg

    I look forward to the conference of the “Friends of Italian Opera” :=)

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  • Ian Liberman

    @Justin if you are referring to me . I am referring to the earth`s velocity around the sun at 29.8km relative to neutrino speed which is slightly less than 300,000km/sec. In 2005, in an article , in physics org., the NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) had determined the absolute speed of the earth travelling through the universe to be about 600 km/s towards the constellation Virgo, due to the Doppler shift of the microwave background radiation. My purpose is to find out where this statement from @Nick came from or why it was reported. ” The experiment equally shows that the earth has a velocity ‘just a bit slower than light’”.

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  • randommuser

    I think Nick has a point. From the point of view of neutrinos (that is, from the reference frame in which the neutrinos are at rest), earth is moving close to the speed of light, which is correct. The correspondence between mass and speed is that the smaller a particle’s mass is, the easier it is (takes less energy) to accelerate it close to the speed of light. It would then appear that from neutrino’s point of view there is an enormous amount of kinetic energy present in the universe, much more than in our reference frame. So how could that be? Is there a reference frame in which the total kinetic energy of particles in the universe is at minimum? Wouldn’t that be a “preferred” reference frame?

  • David Brown

    The OPERA and MINOS teams compared neutrino speeds indirectly to the speed of light with implicit assumptions about the general theory of relativity (GRT). According to Adamson et al. in their 2007 paper “Measurement of neutrino velocity with the MINOS detectors and NuMI neutrino beam” (p. 4), “The arrival time of neutrinos at the FD [Far Detector] is similar, but the relative jitter of the two GPS clocks have a maximum error of ± 200 ns relative to UTC, with a typical error of 100 ns.” (2007 paper by Adamson et al.)
    The ICARUS team compared neutrino speed directly to the speed of light, using a timing method that bypasses possible tiny deviations from Einstein’s GRT. According to Antonello et al. in their paper “Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam”, “The absolute UTC timing signal at LNGS is provided every second (PPS) by a GPS system ESAT 2000 disciplined by with a Rubidium oscillator …, operating on the surface Laboratory. A copy of this signal is sent underground every ms (PPmS) and used in ICARUS to provide the absolute time stamp to the recorded events.”
    The OPERA team originally claimed a six-sigma deviation from the speed of light — if the Rañada-Milgrom effect is empirically valid, then the OPERA team might have confirmed this effect. The OPERA story might not be over.

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  • http:/ James Gallagher

    what the hell? you deleted my comment?

  • http:/ James Gallagher

    ok, maybe a glitch, what I wanted to say was that the “speed of light” law is is with us forever and perhaps even more suprisingly is “3D Space”

    The evolution equation naturally explains renormalisation by subtracting the entire universe

    U(t+tdelta) = exp(hL).U(t) – U(t)

  • Lab Lemming

    Well, sure, they’re 2011 now. They were 2012, but then they traveled back in time!

  • James

    The discussion about Earth’s velocity in the neutrino frame is not particularly interesting or relevant for why the measured speed is close to c. It is simply because the neutrino mass is very much smaller than the neutrino energy. No more, no less than that.

  • Bob

    @randomuser yes, its called the comoving frame. Its the frame in which the cmb is roughly isotropic. Its well understood that in an expanding universe, there is a special frame of reference that is at rest relative to the expansion, i.e., relative to the motion of the distant galaxies. This is perfectly well described by general relativity.
    And yes, I agree with James, this is all rather uninteresting and irrelevant to the opera/icarus results, and I’m surprised this comment section is dominated by discussion of people’s basic misunderstanding of relativity, especially as it affects opera and icarus equally, and so can’t possibly be relevant to the discrepancy in their results.

  •,txt James Gallagher

    Is everyone silly?

  • Tony Mach

    These FTL denieres are all funded by Big Oil!

    Wait, this isn’t Phil’s blog, is it? Sorry, my bad! :-)

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  • Psicologia Barcelona

    I also believe that these deniers CTF is financed by the oil industry

  • Shantanu

    Sean, there were some quotes in press that the superluminal neutrinos is evidence for string theory.
    Now that the this result has been refuted, does that imply that string theory is ruled out?

  • http://google Bidyut

    Both ICARUS n OPERA took into account GR effects.To try to question GR is absolutely absurd.

  • Bob

    @Shantanu, both your premise and conclusion are wrong. In the “standard” formulation of string theory, e.g., the formulation found in Polchinski’s books, relativity and the local Lorentz invariance are exact.

    When the erroneous OPERA result came out, various people tried to become famous by cooking up all sorts of crazy, but ultimately flawed, models of superluminal behavior. This even included some string theorists, who decided to abandon the basic structure of string theory – that had worked so well – and replace it with some ad hoc dicey construction in a desperate attempt to become famous. Well this turned out to be a waste of time.

    So string theory still lives on, by simply recovering relativistic quantum field theory in regimes that are not “too extreme”. But much more importantly: Einstein was right.

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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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