Speed-of-light results under scrutiny at Cern

Opera detector Enormous underground detectors are needed to catch neutrinos, that are so elusive as to be dubbed "ghost particles"

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A meeting at Cern, the world's largest physics lab, has addressed results that suggest subatomic particles have gone faster than the speed of light.

The team has published its work so other scientists can determine if the approach contains any mistakes.

If it does not, one of the pillars of modern science may come tumbling down.

Antonio Ereditato added "words of caution" to his Cern presentation because of the "potentially great impact on physics" of the result.

The speed of light is widely held to be the Universe's ultimate speed limit, and much of modern physics - as laid out in part by Albert Einstein in his theory of special relativity - depends on the idea that nothing can exceed it.

Start Quote

We want to be helped by the community in understanding our crazy result - because it is crazy”

End Quote Antonio Ereditato Opera collaboration

Thousands of experiments have been undertaken to measure it ever more precisely, and no result has ever spotted a particle breaking the limit.

"We tried to find all possible explanations for this," the report's author Antonio Ereditato of the Opera collaboration told BBC News on Thursday evening.

"We wanted to find a mistake - trivial mistakes, more complicated mistakes, or nasty effects - and we didn't.

"When you don't find anything, then you say 'well, now I'm forced to go out and ask the community to scrutinise this'."

Friday's meeting was designed to begin this process, with hopes that other scientists will find inconsistencies in the measurements and, hopefully, repeat the experiment elsewhere.

"Despite the large [statistical] significance of this measurement that you have seen and the stability of the analysis, since it has a potentially great impact on physics, this motivates the continuation of our studies in order to find still-unknown systematic effects," Dr Ereditato told the meeting.

"We look forward to independent measurement from other experiments."

Graphic of the Opera experiment

Neutrinos come in a number of types, and have recently been seen to switch spontaneously from one type to another.

The Cern team prepares a beam of just one type, muon neutrinos, and sends them through the Earth to an underground laboratory at Gran Sasso in Italy to see how many show up as a different type, tau neutrinos.

In the course of doing the experiments, the researchers noticed that the particles showed up 60 billionths of a second earlier than they would have done if they had travelled at the speed of light.

This is a tiny fractional change - just 20 parts in a million - but one that occurs consistently.

The team measured the travel times of neutrino bunches some 16,000 times, and have reached a level of statistical significance that in scientific circles would count as a formal discovery.

But the group understands that what are known as "systematic errors" could easily make an erroneous result look like a breaking of the ultimate speed limit.

That has motivated them to publish their measurements.

"My dream would be that another, independent experiment finds the same thing - then I would be relieved," Dr Ereditato told BBC News.

But for now, he explained, "we are not claiming things, we want just to be helped by the community in understanding our crazy result - because it is crazy".


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  • rate this

    Comment number 285.

    Could it not be that these particles did not travel faster than the speed of light but in fact just travelled a shorter distance than the more massive photons? particles actually follow geodesics in space which is their paths affected by gravitational fields. Does it not follow then that two groups of particles with different masses would follow different geodesics?

  • rate this

    Comment number 284.

    Einstein's Special Theory of Relativity says that objects gain mass as they speed up, and that speeding up requires energy. The more mass, the more energy is required. By the time an object reached the speed of light, Einstein calculated, its mass would be infinite, and so would the amount of energy required to increase its speed. To go beyond the infinite is impossible.

  • rate this

    Comment number 283.

    in response to Mike Solomons' comment. The speed of light is absolute. Einstein's theory says that irrespective of the movement of the earth, solar system etc, the speed at which the photons travel are the same. Meaning that if you walk backwards shining a torch the light will travel at the same speed as if u were walking forward with it. I know it sounds illogical, but that's the theory

  • rate this

    Comment number 282.

    @ Jimenez10: Dawkins would be the first to congratulate these scientists if the result is confirmed by others. You seem to misunderstand the whole basis of science: it is about being open-minded and accepting that rigorous new evidence can occasionally disprove even long-established theories which then must be refined or rejected. Science has no place for blind faith.

  • rate this

    Comment number 281.

    if time is a dimension then it should be possible to travel slower in time than light, therefore making you travel faster that light in the other known dimension.

  • rate this

    Comment number 280.

    Has deformation by tidal forces or gravity fluctuations been considered?
    Over 720km rock is not as solid as you might think and the fixed points could easily move 10cm closer.

  • rate this

    Comment number 279.

    As a scientist I have 2 rather obvious comments regarding the experimental results:
    1 Are you sure the timing delay (and its statistical variation) introduced by the detectors is well understood and characterised?

    2 It would be great to repeat the experiment with the detector positioned further away. There are practical issues with this (!) but a real effect will increase with distance.

  • rate this

    Comment number 278.

    If it were corroborated and could be reproduced - just think of the impact that would have! Part of me would love it to be true but I suspect - when all is said and done - it is more likely practical error than disproof of the General Theory!

  • rate this

    Comment number 277.

    Surprising how many Luddites are coming out of the woodwork... some very entertaining comments.

    One interesting point is that if a neutrino (or anything else for that matter) travels faster than light, according the the special theory it would arrive at it's destination before if left. In other words, time would go backwards.

  • rate this

    Comment number 276.

    #258 for something to travel faster than the speed of light an instance would exist where it travelled at the speed of light. Therefore if you cannot travel at the speed of light you cannot go fast than it. For example you cannot reach 31mph in a car without having previously travelled at 30mph

  • rate this

    Comment number 275.

    Didn't the Sun once orbit the earth?"

    For how long was the Earth flat ?"

    Neither were the result of the scientific method (even Greek knew the earth was round and proposed the heliocentric system). By definition modern science could never accept either as empirical evidence showed neither to be true and inconsistent with a theory of mechanics that explained that evidence.

  • rate this

    Comment number 274.


    The E=MC^2 part of special relativity just just that a part of it.

    the mass of an object with rest mass m is given by e=Ymc^2 where Y is the lorentz contraction factor (put Y=1 for a particale at rest to get E=mc^2) as velocity increases Y increases and is bound by c Y is due to contraction of spacetime and time dialation.

    the reasons are far to comlicated for 400 cha's but..

  • rate this

    Comment number 273.

    People simply don't seem to understand - This is all perfectly possible if the universe is shaped like a donut.

  • rate this

    Comment number 272.

    "is it possible to travel slower through time???"

    Sure. It's called drugs... ;)

  • rate this

    Comment number 271.

    Is this experiment conducted in a vacuum like at the LHC? Would have been a useful bit of information. If not the speed of light can still be calculated anyway but would no longer be a constant.

    I do applaud the attitude of the scientists involved though. Hopefully someone will have some answers soon :)

  • rate this

    Comment number 270.

    I am not good in physics but I like it. It is fascinating. News like this is so exciting. Yes, maybe there are mistakes, maybe the calculation is wrong, or maybe even the theory of the speed of light is incompleted, but all these researches/tests give us hope. Hope that one day we can use the technology to discover other world, and travel through space can become possible.
    So yes, great news.

  • rate this

    Comment number 269.

    "a speed greater than the phase velocity of light"
    Not speed of light. Note you can have a negative phase velocity, you can't have a negative speed. They are not the same thing.

  • rate this

    Comment number 268.

    is it possible to travel slower through time???

  • rate this

    Comment number 267.

    Maybe Soddy's skepticism of Relativity was thoroughly justified?

    "Possibly the Einstein relation is a one-way relation only between mass and energy not between energy and mass, or even more probably, it may not be strictly true at all, as mathematical infinities do not occur in Nature."


  • rate this

    Comment number 266.

    Let's not start running down Einstein because after all he did not even have a calculator when he came to his conclusions. Have you ever tried measuring the speed of light on a slide rule?

    There will always be new discoveries and understandings so what's the big deal. Maybe we don't fully understand this because after all we were living in trees just 30 seconds ago in age of Universe terms.


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