September 25, 2011 AT 1:00 pm

Why the Faster-than-Light Neutrino Experiment May Be Wrong

Interesting article from the Bad Astronomy Blog at Discovery.com:

So the web is buzzing right now over news that scientists have detected some subatomic particles moving faster than the speed of light.

Yeah, well, not so fast. Let’s think about this for a sec.

First, what happened is that they create these particles, called neutrinos, at CERN in Geneva. Neutrinos don’t interact with normal matter well, so they can pass right through the Earth as if it isn’t there. In a fraction of a second, some of them enter a detector called OPERA in Italy where they are recorded (pictured here). If you divide the distance between those two points by the time it takes for the neutrinos to travel, you get their speed.

And when the scientists did that, they find the neutrinos get to Italy about 60 nanoseconds faster than a photon would.

The thing to do is to look at where this claim might have gone awry. First, the timing is interesting. They claim a measuring accuracy of 10 nanoseconds, so 60 ns would be pretty significant. However, my first thought is that light travels about 30 centimeters in 1 ns, so they need to know the distance between the source and the detector to an accuracy of 3 meters. If they are off by 20 meters, then we’re done; that would explain the difference entirely. I suppose this depends on how they measured the distance and the speed of the particles, too. However, they haven’t published a paper on this just yet, so that’ll have to wait.

Also, as pointed out in a Science Magazine article, knowing the exact moment the neutrinos are created isn’t easy either. Mind you, 60 nanoseconds is 0.00000006 seconds, so they need a pretty good clock here. That page also says they used GPS to determine the distance, which could be off a bit.

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  1. The preliminary report can be found here: http://static.arxiv.org/pdf/1109.4897.pdf It is an interesting read.

  2. trouble is, these are CERN researchers we’re talking about, not some middle school science fair experiment, and I’d really hope that all these “obvious” factors had already been factored in. “Oh sorry, we had the GPS systems in +/-10m mode. Never mind.” ?? Can’t see it.

  3. From CERN’s press release on this matter:

    “The distance between the origin of the neutrino beam and OPERA was measured with an uncertainty of 20 cm over the 730 km travel path.”


    The author of that article really should go straight to the source of the information.

  4. I really doubt that it’s as simple as inaccurate distance.
    That would be one of the easier things to check, and the GPS locations wouldn’t be found by consumer grade GPS, but the type used to measure ground movement for faults and volcanoes. Some surveying GPS setups have 2 mm accuracy. There may be better, not seeing in in my 2 minute search.

    Another “dumb mistake” way it could be an error would be if they measured distance over the surface rather than between the 2 points through the crust of the earth.

    This would have been reviewed by multiple scientists looking for flaws before they made the announcement.

    It’s not necessarily something that breaks general relativity, even if similar results are found with future tests at different sites that are being planned now. While there’s going to be lots of speculation, those results are needed before any conclusions can be drawn. Among other things, differences in the time based on different distances will help determine what is happening.

  5. This article appears to disprove some of the points presented by Science Magazine: http://www.newscientist.com/article/dn20961-fasterthanlight-neutrino-claim-bolstered.html

    Particularly, it mentions the precision of their measurement of physical distance. It claims that the tolerance is +/- 20cm, well under the 3 meter figure given in the original article.

  6. My reaction to the faster than light stories is the same as the reaction I had to Cold Fusion. “In a relatively short time, it will be demonstrated to be incorrect. Just relax and wait.” Sure enough, in about a year, the consensus opinion became that honest and sincere scientists had made a measurement error. What’s new?

    Light, being ELECTROmagnetic, interacts with matter. The published speed of light is specified in a VACUUM. In a glass lens or prism, light moves at about thirds of its published velocity. The speed of an electric pulse moving down a length of coax is about half of the published speed of light. In the last large stellar super nova about a decade ago, the neutrinos arrived at earth 3 DAYS before the light arrived. Why? Because space is not a perfect vacuum! Neutrinos, with their neutral charge are not slowed by interaction with other matter. If they do not crash into an atom and get destroyed, they boogie on by at the speed of light. But the hydrogen and dust in the “vacuum” of space do slow the light a bit, thus the delayed arrival. Could this be related to the tiny discrepancy observed in Italy? I wonder.

    I would doubt GPS as the source of error. The highest accuracy (measuring carrier phase) requires a military password, but if you take data for three days, you get your absolute position to a millimeter (0.04 inches). The Navy measures the satellite positions to wavelengths of light. I’d first look at the cesium/rubidium traveling clocks. I’m gonna watch from the sidelines.

  7. xkcd as the scoop…

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