More on super-luminal neutrinos

Schematic of an early solar neutrino detector

It appears the articles the broke yesterday about neutrinos breaking the light-speed barrier were based on solid science (I can’t believe I just wrote that!). More here:

Over three years, and from 15,000 neutrino “events,” a huge detector at the Italian center deep under mountain rock recorded what OPERA spokesman Antonio Ereditato described as the “startling” findings. He said his team had high confidence they had measured correctly and excluded any possibility of some outside influence, or artefact, affecting the outcome. “My dream is now that other colleagues find we are right,” he added.

OK, admittedly my particle physics has turned to rust over the years. I recall there was some debate over whether or not neutrinos had a rest mass. Was that ever resolved? If they do, then either the mass equation for Special Relativity has to be adjusted, or those particles hit the detector with one hell of a wallop. More than a wallop, theoretically their mass would be greater than infinity on the north side of the speed of light. And if they have no rest mass, and went faster than light, that should open up all kinds of cans of worms in quantum physics.

Without getting all excited and biased, just for fun, let’s stipulate they did beat the speed of light. What’s your guess? Some kind of EPR effect where entanglement transfers into a particle, specifically a neutrino, at the other end? In this case knowing if pairs of particles were made at the origin very close together in time, say an average of 60 nano-seconds apart, might count for something. Some sort of reverse decay event that went anti-time to preserve symmetry or some other book keeping deal? Frankly I have no idea how anything like that would work, but then like I said, my last low level graduate physics class was over 20 years ago and these results, if confirmed, would probably make that course officially obsolete.


  1. Dave Hassan says

    To the neutrino mass question: yeah, they have mass, and there are 3 mass eigenstates, one for each lepton. In fact, solar neutrinos oscillate between the 3 eigenstates. This was the cause of a big problem for a while in measuring neutrino masses–the solution was to realize they oscillate between the states.

    To the other question…I really have no idea. I would say probably not some non-locality thing, because I think that would violate not just locality but causality which is possible but I suppose less likely.

    On another note, this is much more interesting than a Higgs event for sure.

  2. thztds says

    Neutrinos do have a rest mass, but it’s less than 0.28 eV by the 2010 measurements. Regardless, particles that go faster than light do not have infinite mass, they have imaginary mass. In fact, the faster they go, the closer they get to their rest mass, but it’s just that the value is an imaginary number, not a real one. Of course, what a complex value mass means is quite beyond my ability to imagine.

  3. fastlane says

    Yeah, the more I read about this, the more it seems the measurements are accurate. Obviously, it will take some time for others to confirm this or find the flaw.

    It makes me want to go back and find a course in modern quantum mechanics at the local university. I only have had up to an introduction to relativity, and that was a science elective, purely based on personal interest. (and it was almost 20 years ago.)

  4. aziraphale says

    “theoretically their mass would be greater than infinity on the north side of the speed of light.”

    I think in fact the equations say the mass would be imaginary. What that does to conservation of energy I have no idea. I suppose they could be created in pairs with equal and opposite imaginary masses.

  5. ftltachyon says

    Last I remember, the conclusion was that the neutrinos had very small but nonzero rest mass.

    If this is true, a hell of a lot about relativity has to be adjusted. It would give physics the observation it needs to start working on the next generation of theories. If it’s true, the explanation for what’s happening won’t be anything that’s allowed or possible given current theories.

    However, I think it’s far more likely that the final conclusion will be that some method used for measuring either time or distance, probably one which is accepted by the community as a gold standard, turns out to have some systematic error in it. Call me a cynic, but I remember plenty of science-by-press-release discoveries which turn out to have a fraction of the meaning that the headline implies.

  6. robb says

    IANAPP* but i believe it turns out neutrinos do have a small mass. neutrinos oscillating between flavors is a consequence of mixing of the eigenstates between flavors and masses. as the phase of the mixing changes, so does the particular eigenstate you happen to measure.

    *i am not a particle physicist.

  7. monad says

    I recall there was some debate over whether or not neutrinos had a rest mass. Was that ever resolved?

    This was more or less decided with the solar neutrino problem. A detector found the missing neutrinos were there but in a superposition of states, oscillating between electron and muon types. That only works if they have some mass, although I’m not sure what was supposed to differentiate them otherwise.

  8. binjabreel says

    I gotta say, I read those braying “Incredible new breakthrough!!” articles all the time, but this one… The more I read it, the more I find myself getting that crazy nerdy thrill I haven’t felt since I first really started to understand relativity and (what little we understand at all of) quantum mechanics.

    Because even if it’s just some universal sleight-of-hand bookkeeping trick that makes these things appear to travel faster than the speed of light, that’s still (cue frantic teenage girl hand-waving) FRICKIN’ AMAAZING!!

    Like, jumping around the physics lab giggling like an idiot amazing.

  9. says

    I study particle physicist, and I really don’t believe in this result.

    If this measurement was true it wouldn’t mean that neutrinos are tachyons, because we know they are not from countless other experiments; rather, it would mean that Lorentz invariance is broken. But a coefficient breaking Lorentz invariance at the 10^-5 level would have many consequences in particle physics which we would already have seen. For example, electron positron scattering would also have to break Lorentz invariance -naively we could put that effect at around 10^-10- and those experimental constraints are very good.

    We also know that electron neutrinos travel at essentially the speed of light from the supernova 1987A, consistent with special relativity. But there are very strong experimental bounds on the difference in speed between electron and muon neutrinos; something like 10^-22 for some coefficients that parametrize it. (; this is because if different neutrinos travel at different speeds the neutrino oscillations are changed.) So we have lots of information on neutrinos behaving according to a relativistic quantum field theory.

    I think there must be systematic errors either underestimated or


Leave a Reply