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FTL Neutrinos Explained... Maybe

Posted by Soulskill on from the a-definite-possibility dept.

The Bad Astronomer writes "A new paper, recently posted on the arXiv physics preprint server, claims to have explained the faster-than-light neutrino experiment from last month. The author claims the motion of the GPS satellite introduces a relativistic dilation that accounts for the now-infamous 60 ns discrepancy in neutrino flight time. However, I'm not so sure; the original experimenters claimed to have accounted for relativistic effects. I don't think we've seen the end of this just yet."

8 of 226 comments (clear)

  1. Having Read Both Papers by eldavojohn · · Score: 2, Interesting

    (Although I am not a physicist) I understand that this is talking about the concept of "time" from a frame of reference between the GPS satellites and the ground stations. However, the original paper's implementation did not measure time with GPS satellites (that would be silly). Instead, it used the satellites to obtain very precise distances and when they did this, they accounted for relativity. The time recording devices were atomic clocks at the locations of the facilities on the surface of the Earth. As the second article notes, they just said they did this and you assume they did it correctly. However, if they miscalculated relativity between the satellites and ground stations, it's going to be in the form of the distance being incorrectly measured -- not the actual time itself. And that distance (which would be slightly shorter than they calculated) should then result in an explanation of the nanosecond difference.

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    1. Re:Having Read Both Papers by ETEQ · · Score: 5, Interesting

      (I *am* a physicist) Actually, the original paper *did* measure time with GPS - more to the point, they use GPS to establish a common frame between the two locations. Look at Figure 5 of the OPERA paper (http://arxiv.org/pdf/1109.4897v1).

      Having said that, as other replies have noted, this kind of correction is well-understood, so while it isn't explicitly laid out as far as I can tell, it's unlikely the OPERA group screwed this up. What may well be true, though, is that there may be systemic offsets either in the GPS timing system, the implementation at Gran Sasso (they actually have a big waveguide that they run from the Earth's surface all the way to the GPS reveivers they have by their detector deep underground), or any of the myriad corrections that were needed to determine the time-of-flight baseline (although as far as I can tell they worked very hard to get this measurement right...).

      It's also rather suggestive that the author of this paper has no particle physics (or even physics) credentials. So he/she probably doesn't know the OPERA collaboration's processes very well (admittedly, these details should be in the paper, but the tradition of the community is to not do that sort of detail in announcement papers like this...)

    2. Re:Having Read Both Papers by tftp · · Score: 5, Interesting

      60 ns translates into 18 meters at the speed of light. If the error was that large any car GPS device would be showing you as driving on some other street.

      I was working with some high precision GPS receivers, and they can place you on the map with accuracy of a couple of centimeters. The shape of the Earth is also pretty well understood now.

      One unfortunate possibility would be that the clocks are wrong. They had to move them between sites, since they weren't willing or able to synchronize them over the radio where they are (the varying propagation paths would be hard to deal with.) A more pleasing (to me) outcome would be that FTL is real.

    3. Re:Having Read Both Papers by tftp · · Score: 3, Interesting

      Not if the map is also off by 18 meters. How do they put the roads on the map in the first place? Most likely, by GPS, or whatever GPS was calibrated against when it was implemented.

      The current datum for GPS is WGS84. Locations of many places on Earth were carefully measured for centuries, using astronomy and trigonometry. I don't know if they are accurate enough to calibrate the GPS.

      A systematic, uniform error, like a translation of the entire datum, would have no effect on the OPERA experiment - however you slide or rotate the outer shell of a sphere it doesn't change the distance between two points. It would require a systematic but non-uniform error to cause this effect. I guess it is possible, since there is no explanation so far of the OPERA results. Such an error has to be location-specific and it should be invisible to the WAAS.

    4. Re:Having Read Both Papers by julesh · · Score: 3, Interesting

      The word "infamous" is often used by scientists to describe problems that a large number of people have attempted to solve and have failed. I suspect that this is the sense the submitter was using it in.

  2. Re:Garbage by Windcatcher · · Score: 2, Interesting

    I won't call it "garbage", but otherwise I was thinking along similar lines (disclaimer -- I have a Master's in Physics but I haven't bothered to do the math). 60ns is an eternity in an experimental setup, and while the two sites are at different latitudes (and a straight-line three-space trajectory sends the neutrinos along a curved path in spacetime), I can't see earth's relatively weak gravity accounting for such a discrepancy. It's a curved 4-space path, but it's not *that* curved.

  3. bogus by bcrowell · · Score: 5, Interesting

    It's bogus. (Yes, I am a physicist.) OPERA used portable atomic clocks, which were moved to the the two labs and then synchronized via GPS (see this article). GPS thoroughly incorporates general relativity (which includes special relativity). It has incorporated GR ever since it was first built, because if it didn't, it wouldn't work. At all. No, not even well enough for hiking and driving. Here is a review article on relativity in GPS. GPS uses coordinates called Earth-Centered Inertial (ECI). These are coordinates (t,r,theta,phi), where the spatial coordinates are spherical coordinates that rotate along with the earth, and t is the time coordinate of a hypothetical observer in a nonrotating frame at rest relative to the center of the earth. General relativity is completely agnostic about what coordinate system you use, so this choice of a coordinate system is not a choice that has any physical significance; it's just a bookkeeping thing. Van Elburg assumes that GPS was constructed by people who didn't understand relativity, and therefore GPS times need to be corrected for relativistic effects. That's just completely wrong.

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  4. Highly Doubtful by Roger+W+Moore · · Score: 5, Interesting

    Maybe its because GPS understands relativity well enough to get planes to the correct runway...

    GPS understands relativity well enough to require General Relativistic corrections. This paper suggests that the GPS clock is inaccurate and suffers a lag based on location which, since GPS requires accurate timing to pinpoint your location a 64ns time difference would put you 20m off your correct location. In addition the author uses a very simplistic model of GPS clock and satellite for getting the clock. I would also have assumed that the GPS clock is based on multiple satellites since it has to know your location to calculate the propagation delay and it does this by comparing one satellite clock to another.

    However the final nail in the coffin is that he doesn't know how to spell photon (it is not spelt foton!)...so I have extreme doubts that this is paper is correct. In fact I'd need to hear from a GPS expert that his simplistic model is reasonable because I don't believe that it is (but then I'm not a GPS expert!).