FTL Neutrinos Shake Up Physics Community

The Speed of Light might not be the Universe’s ultimate speed limit. Almost a century of testing seemed to show that no particle in the standard model could travel faster than the speed of light. Until now.

An Italian team of physicists firing a beam of neutrinos through more than 700 km of rock has discovered a small discrepancy, in more than 15,000 tests, some of the neutrinos arrived earlier than they should have, suggesting that they were travelling faster than the speed of light.

This is an incredible finding, and if it is validated through independent testing it could overturn the current understanding of physics.

What exactly happened?

The OPERA experiment is a giant underground detector designed to detect spontaneous neutrino transformations in a beam fired from CERN, through 732 km of rock to the OPERA detector in Italy.

Neutrinos are subatomic particles which are created by nuclear reactions and radioactive decay. They have very small, but non-zero mass, are electrically neutral (which allows them to pass through large amounts of matter without interacting with it) and move at speeds very close to the speed of light.

Sometimes, neutrinos can spontaneously change from one type of neutrino to another. The OPERA experiment was firing muon neutrinos and looking for transformations into tau neutrinos. The different types of neutrinos are called “flavours” and these transformations between different flavours are called neutrino flavour oscillations.

The OPERA experiment measured more than 15,000 bundles of neutrinos fired from CERN and discovered that the travel times are a few billionths of a second shorter than they should be. This may seem like a tiny difference. What can you do in a billionth of a second? Humans can’t even detect such a tiny fraction of time without mechanical assistance.

Light would cover the distance between CERN and OPERA in 2.4 thousandths of a second at almost 299,792,458 meters per second. The neutrinos are covering that distance 60 nanoseconds faster than light. 60 billionths of a second.

A fusion reaction inside a hydrogen bomb takes 20 to 40 nanoseconds.

The OPERA experiment may have just demolished the accepted theory that nothing can travel faster than the speed of light.

The speed of light is a fundamental constant in physics; we use it to establish the length of a meter. Until now, the speed of light has been accepted as the maximum speed at which light, energy, matter and information can travel in the universe.

Why is the speed of light the “speed limit”?

Albert Einstein came up with a little calculation in 1905 which goes like this:

E = mc2

If we translate that into English it states that the energy of a particle is equal to its mass multiplied by the square of the speed of light. Because the speed of light is so high, this means that even very low-mass particles contain a LOT of energy (hence the hydrogen bomb).

Einstein’s theory of Special Relativity has two other predictions (proven by experiment):

  1. The length of moving objects contracts, and this contraction is more extreme the faster the object is travelling.
  2. Moving clocks run more slowly the faster they are travelling.

For any particle trying to travel at (or extremely close to) the speed of light, these three principles come into play. The object becomes exponentially heavier as it approaches the speed of light, its length contracts and time slows until the factor (y) by which it’s length contracts and time dilates becomes infinite.

The Lorentz factor γ as a function of velocity. It starts at 1 and approaches infinity as v approaches c.

Thus, as far as we understand the universe, nothing, no particle, no packet of information, can travel faster than the speed of light.

How do we explain the OPERA observations?

  1. Oops, we made a mistake. Someone put in a few too many zeroes when they were setting up the calculator and it was all a big misunderstanding. I’m pretty sure that this is not the case. The OPERA team has made a lot of observations, found a consistent result and has gone to great lengths to check all their procedures to make sure that this was not an error, simple or otherwise. That doesn’t mean that the observed phenomenon is not due to some error or a variable that was not fully accounted for, but we won’t know until the paper is printed and put through rigorous scientific scrutiny.
  2. Oh! They aren’t our neutrinos but come from another source. D’oh! Again, the team has tested so many individual packets that it is probable that they are measuring their own neutrino stream. But, because neutrinos are produced in the nuclear reactions of the stars (amongst other sources) all around us and can travel great distances without interacting with baryonic (normal) matter, it is possible that the “faster than light” neutrinos actually come from somewhere else and were picked up on this detector by accident.
  3. These neutrinos are actually travelling faster than the speed of light! The results from the OPERA experiment are not conclusive, but they are certainly pointing and waggling their eyebrows. We may just have discovered particles travelling faster than c! Now, we need peer review and attempts to repeat the experiment by other teams which show the same result.

Does this mean that physics is not a good way to know our universe?


Physics and the tools it gives us are the best way that we have to understand our universe. It is built on the incremental removal of doubt. The slow and steady progress of testing and re-testing our ideas to eradicate the wrong ones and built upon the right ones.

This is exactly the kind of (potential) discovery that shows the power of physics and the robust nature of the system to re-evaluate and move forward.

Testing by other teams of physicists is extremely important at this point. We need as many minds as possible to work on this and see if it is what we think it is.

This is not going to give us faster than light spaceships

Because spaceships and everything that goes into them weigh a great deal more than a neutrino. We might be able to go very fast by shooting a stream of neutrinos out of the back of a spaceship, but c is still reserved for light beams and particles with negligible mass.


18 responses to “FTL Neutrinos Shake Up Physics Community

    — James Ph. Kotsybar

    Oh, little neutral one of tiny mass,
    who flies anomolously from the sun,
    you zip through matter photons cannot pass:
    Could this explain the races you have won?

    From Einstein, few believe that it could be
    that any mass can go as fast as light —
    it’s deemed complete impossibility,
    assuming Relativity is right.

    If proved, the implications terrible,
    will give complacent physicists a scare.
    In terms that twist the ancient parable
    it’s you that’s tortoise; the photon’s the hare.

    It seems, though steady, light can’t keep up pace.
    You oscillate, and yet you win the race.

  2. I think the problem of relative velocities of the earthbound locations and the GPS satellites to synchronize their clocks accounts for the anomaly. It’s not enough to repeat the same effect in the same laboratories using the same equipment and methodologies, you need to repeat the same effect elsewhere, using different equipment, and use a synchronization method that isn’t dependent on GPS satellites. Also, since the GPS satellites themselves rely on Einstein’s relativity to report positions correctly, it might be a problem with the satellites trajectories.

    People jump to conclusions so quickly, and then report it as “breaking news”, when nothing is confirmed. An interesting anomaly in an experiment, to be sure, but not one that warrants bringing out new maths to explain what might be something known, but not accounted for.

    • I definitely agree that it would be best if the experiment could be repeated with different equipment somewhere else.

      However I do not agree that the GPS satellites account for the speed observed. Prof. Chad Orzel sums it up nicely in his post on scienceblogs:
      1. The source is not particularly reliable – the GPS clocks explanation was published on a Physics Arxiv blog which is not affiliated with the Physics arxiv itself. This is not a death knell on it’s own, but part of the problem.
      2. To quote Prof Orzel directly “what we have here is a single-author preprint from somebody in the Department of Artificial Intelligence at a Dutch university, claiming to have found an issue that was missed by a large collaboration of physicists”
      3. again, I quote “I think the author of the preprint is also confused about the way the experiment worked. That is, he seems to be assuming that all of the timing information comes from the GPS clocks, which are moving relative to the experiment, when in fact the actual event timing comes from clocks on the ground that are at rest with respect to the source and detector. ”

      Please read the rest of Prof Orzel’s article here: http://scienceblogs.com/principles/2011/10/experimentalists_arent_idiots.php

      And a more technical explanation is here:

      (Sorry if this is a bit rushed, but I am at work – we will be including this in Episode #33 of Consilience, the podcast which is linked to on my home page, if you would like to have your opinion heard, I’ll be happy to include it.)

  3. Would a 4th explanation of the observation be that the speed of light is variable and different in the location of the experiment?

    • The variability of c is dependent on the medium through which the light is travelling. In this experiment you will see this given as “Speed of light in a vacuum”. While 732 km of solid rock can not be considered a vacuum for light, it can be for neutrinos which interact with barely any matter at all.

      • I was actually offering that another explanation could be that the speed of light is not constant in all areas of the universe (regardless of media). I know that comes off as fatuous, because we take the constancy of c in vacuo for granted. But I think it’s important in science to consider all the possibilities (even the unlikely or counterintuitive ones) after early experiments. Until the scientific community confirms these findings and devises new tests (with rigor and falsifiability!), it’s ok to speculate on all the conditions.

  4. Why is it, that when a car drives 120km/h (from your point of view), c as observed from that car is still c? (And not c – 120 km/h?) Simple: the laws of physics should be (and are!) the same for everyone (every observer) in the universe, and c follows directly from certain laws (Maxwell’s equations).

    Allowing speeds > c, is allowing that for some ‘observers’ (neutrinos or that sail-ship) c seems relatively slower and more importantly: is allowing that for some observers the laws of physics are different.

    (The ‘observer’ is so important in relativity.. )

    I don’t believe it for a bit. I’m hoping for a definitive answer yesterday! (Bad causality joke ;-))

  5. I’m pleading the argument from personal incredulity here. I can’t accept option 3, so it can’t be true. QED. The calibration of such a machine to detect such a shy partical must be to blame, or the GPS system for recording the relative start and end positions.

    “Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws. “Douglas Adams

    • The margin for error on this experiment is so tiny, and the possible ways it can go wrong so numerous that I also find it hard to accept that this is not an error.

      But damn! It would be so cool if this actually is FTL!

  6. Hi, I think there might be an error, either here or on another post about the story.

    “Light would cover the distance between CERN and OPERA in 2.4 thousandths of a second at almost 299,792,458 meters per second. The neutrinos are covering that distance in 60 nanoseconds. 60 billionths of a second.”

    The neutrinos are ALSO covering the distance in 2.4 thousands of a second. but at about 60 nanoseconds faster give or take 10 nanoseconds.

    What you are saying here is that the neutrinos are covering the distance at (and my math sucks so this could be wrong but the theory is sound :P) 12 200 000 000 Km/s while speed of light is 299 792.458 Km/s


    Hope this helps.

    • oh! Thanks for pointing that out!
      I wrote this in quite a hurry between a bunch of work-related disasters, will fix it right away, thank you!

    • Oh and sorry if my post comes off as displeased or anything I LOVED your write up, Really good! just the “small” error 😀

    • a light-year thick lead sail? Are we “assuming a spherical sheep” here?
      How much would that even weigh? I don’t want to nail my colours to the mast here too much, but I’d be willing to say that accelerating something that massive to relativistic speeds would be impossible!

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