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FTL Neutrinos Explained... Maybe 226

Posted by Soulskill
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."
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FTL Neutrinos Explained... Maybe

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  • by eldavojohn (898314) * <eldavojohnNO@SPAMgmail.com> on Saturday October 15, 2011 @07:13PM (#37726724) Journal
    (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.
    • GPS already normally accounts for relativity.... nothing new there. Base on the original paper I think it's highly unlikely they mismeasured the distances. http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html [ohio-state.edu]
      • by Vellmont (569020)

        The paper doesn't claim that the distances were measured incorrectly, it claims the timing was inaccurate do to special relativity (not general relativity which another poster in this thread was confused by.

        In essence, the paper makes the claim that the experiment is using GPS as a reference clock, and the reference clock (the satellite) is in motion differently, relative to the neutrino source, and detector.

      • by tftp (111690) on Saturday October 15, 2011 @09:42PM (#37727560) Homepage

        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 [trimble.com], 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.

        • by Rich0 (548339)

          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.

          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.

          I'm not qualified to judge if the paper is right, but it is very easy to get into circular reasoning when it comes to standards - deriving true standards to that level of precision is hard so lots of stuff gets derived and if anywhere on the chain something goes wrong you can get lots of results that agree and yet are all wron

          • by tftp (111690) on Saturday October 15, 2011 @10:50PM (#37727884) Homepage

            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 [about.com] 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.

            • by Frnknstn (663642)

              Not that I am saying this was the cause for the discrepancy, but a uniform error COULD cause distance measurement errors, because your assumption is incorrect: the earth is very much not a sphere.

              • by ultranova (717540)

                the earth is very much not a sphere.

                According to Wikipedia [wikipedia.org], the maximum distance from Earth's center is at the summit of Chimborazo, 6,384.4 kilometers from center. The lowest is the floor of the Arctic Ocean, 6,352.8 from the center. This makes for a difference of 31.6 kilometers. Dividing this difference with either of these - or any of the various mean radiuses in the linked page - gets a deviation of less than 0.5 percent from a perfect sphere.

                In other words, Earth is very much a sphere.

          • by Patch86 (1465427)

            Unless you believe that map-making started with GPS in 1994, then obviously not.

            Most map making is done with aerial photographs mixed with good-old-fashioned triangulation-based surveying, which is then reconciled with GPS. The error ratios in GPS are well understood, as the system has been used to check against other methods in this way almost continuously since it came online. If GPS positioning was throwing up 18 metre errors left and right it would have been noticed many many times.

      • Not only that, but my understanding is that GPS timing was used only for time-transfer purposes, to calibrate the local cesium standards were used for the actual measurements.

        The bug in the measurement, if there is one, cannot possibly be related to the use of GPS for timing.

    • by Dan East (318230)

      I don't understand this as well. Either this is simply a preexisting inaccuracy in all GPS readings due to relativity that has never been taken into consideration (highly unlikely), or there's something else going on that I don't grasp. I don't see how the neutrino motion relative to the motion of the satellites is a factor here, as no direct measurement between the two is being made in that way.

      One of the things the GPS system helped prove was that relativity is real and must be accounted for in systems o

      • by MichaelSmith (789609) on Saturday October 15, 2011 @07:48PM (#37726876) Homepage Journal

        Maybe its because GPS understands relativity well enough to get planes to the correct runway, and cruise missiles to their target, but the people who designed it didn't anticipate measuring the speed of neutrinos.

        • Highly Doubtful (Score:5, Interesting)

          by Roger W Moore (538166) on Saturday October 15, 2011 @08:32PM (#37727106) Journal

          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!).

          • Re:Highly Doubtful (Score:5, Informative)

            by digitig (1056110) on Saturday October 15, 2011 @09:05PM (#37727334)

            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!).

            I'm not an expert either although I have worked on GPS aircraft navigation and augmentation systems. You are right that the GPS clock is based on multiple satellites. A GPS fix needs a minimum of four satellites, and the receiver triangulates position in 4-dimensions: the three spatial dimensions and time (four unknowns, four data points). What's more, those 4 will not be in the same plane (the satellites themselves form 6 orbital planes), so the bit in the article about "The orbits of these satellites are at 20.2 106 m from the earth’s surface in a fixed planes inclined 55 from the equator with an orbital period of 11 h 58 min [3]. This implies that they fly predominantly West to East when they are in view of CERN and Gran Sasso, which is roughly parallel to the line CERN-Gran Sasso" looks to me like a fundamental misunderstanding of the satellite orbits. The satellites on which a time fix is based will not all be travelling in the same direction. It is possible to use other position information as data points, and so reduce the number of satellites needed for a fix, but I'm not sure why anybody would do that when they can improve accuracy by using all visible satellites (and anyway, even if they did use a single satellite plus accurately known spatial position, the author of the paper still wouldn't know which orbital plane the satellite used was, and so wouldn't know the direction of movement).

          • by khallow (566160)

            However the final nail in the coffin is that he doesn't know how to spell photon (it is not spelt foton!)...

            Not every language spells photon as such. For example, Dutch, the language of the author, spells it as foton [google.com]. So yes, photon is spelled "foton", just not in English.

            As to the paper, the sort of error that supposedly happened with GPS, strikes me as the sort of error that would not be corrected by the system since it's not relevant to GPS's primary task, positioning to within tens of meters. It's particularly suspicious given that it is of the right size to explain the anomaly.

            • by Q-Hack! (37846) *

              As to the paper, the sort of error that supposedly happened with GPS, strikes me as the sort of error that would not be corrected by the system since it's not relevant to GPS's primary task, positioning to within tens of meters. It's particularly suspicious given that it is of the right size to explain the anomaly.

              Not sure why you think that GPS's primary task is positioning to within tens of meters. For military and scientific research, GPS is capable of getting down to within +/- 6 inches. The article doesn't state, but I would assume they are using the far more accurate Differential GPS often referred to as DGPS. [wikipedia.org]

              The only time GPS was accurate to within tens of meters, was when they had the SA turned on to limit enemy use of the system. That was abandoned years ago.

              • by khallow (566160)

                Not sure why you think that GPS's primary task is positioning to within tens of meters. For military and scientific research, GPS is capable of getting down to within +/- 6 inches. The article doesn't state, but I would assume they are using the far more accurate Differential GPS often referred to as DGPS.

                DGPS includes one or more local reference points and hence, isn't strictly a function of GPS. I did forget that military and certain other uses do get more accurate placement, but they don't get the accuracy of DGPS.

          • by snowgirl (978879)

            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!).

            The author is Dutch. In Dutch, it is spelled foton [wikipedia.org]. You can't blame everyone for speaking English as a second language.

    • by flosofl (626809)
      I think the fact that most of us are not qualified to understand the raw data let alone the analysis, lends to believe this summary (and associated article) are vastly oversimplified.

      That it's taken a relatively decent amount of time for this to come out leads me to believe that the answer is non obvious and non trivial to obtain.
    • by shentino (1139071)

      A network where big fat milliseconds are eaten up merely by the speed of light delaying things imply an uber extreme tolerance requirement.

      I'd double check and see simply if error bounds are tight enough.

    • by ETEQ (519425) on Saturday October 15, 2011 @09:13PM (#37727386)

      (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...)

      • by cloricus (691063)

        The summary uses the word 'infamous' to describe the original announcement. In my mind it could only be considered infamous if they made a simple and blatant error. As it looks to a layman they have made an error but in finding the error physics will gain some interesting knowledge it didn't have before. If the latter is true then I'd imagine this would be remembered for all the right reasons not all the wrong ones.

        Would this be the case or is the physics world full of jerks?

  • Garbage (Score:5, Insightful)

    by Goaway (82658) on Saturday October 15, 2011 @07:22PM (#37726776) Homepage

    This is another easy-to-digest paper written by someone who doesn't have the first clue about what was actually done in the experiment, trying to explain it with undergrad physics. And the press jumps on each and every one of these, no matter how bad they are.

    In this case, GPS clock synchronization to nanosecond levels is regularly done in meteorology, the relativistic effects are well known and compensated for, because it wouldn't work at all if they weren't, and the synchronization was confirmed by a non-GPS method.

    Absolutely nothing to see here.

    • Re: (Score:3, Interesting)

      by Windcatcher (566458)
      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.
      • Its complete garbage.

        In order for their experiment to succeed they needed extreme target accuracy, to within 1 meter. This requires they be off by 20 metres. The fact that their experiment succeeded at all for their original purpose kills this bullshit right off.

    • Agreed. If this problem existed then the GPS and satnav industries wouldn't exist because it wouldn't work.
  • by Dr. Spork (142693) on Saturday October 15, 2011 @07:37PM (#37726832)

    In case you wondered this, check out what could be the world's greatest article abstract: Can apparent superluminal neutrino speeds be explained as a quantum weak measurement? [arxiv.org]

    Seriously, it's worth clicking, and understanding the abstract doesn't require advanced physics knowledge.

  • My money is on the fact that the true path of the beam was not from one city to the other, but from the spot where one city was when it started to where the other city was when it stopped. If the path was opposite the rotation of the earth, that'd be very slightly shorter right? Earth doesn't spin fast compared to the speed of light, but this error wasn't very large either
    • by tftp (111690)

      Earth is not just rotating around its axis. Earth is also rotating around the Sun, and the Sun moves on its orbit within the Galaxy, etc. etc.

      Earth's orbital speed is about 30 km/s. The test distance is 730 km. Neutrinos traveled the same path in 2.4 ms. Earth during this time moved by 30 km/s * 2.4 ms = 72 meters. Since the neutrino was emitted at the speed of light, even though the source was receding, it can be interpreted as if the receiver was closer to the source than anticipated.

      If the Earth's v

      • by GryMor (88799)

        Only relative motion matters, aka, in the inertial frame of the source when the leading edge of the beam was emitted, how much has the target moved by the time the leading edge of the beam reaches the detector.

        At two points opposite each other on the equator, that distance would be less than 2.3 meters, with only 730km separating the source and target, that distance is only a few centimeters (the source and target have nearly the same velocity)

  • I wonder of OPERA is receiving messages from the future now, and if so, what they say?

  • If neutrinos were faster than c, the neutrinos from SN1987A would have arrived "five years sooner," [newscientist.com] while they were measured arriving "3 hours before the dying star's light caught up" as expected...
    • Damn. Good point.

      • But then the article doesn't say if anybody was looking five years before the supernova, or if there has been any attempt to find a pulse of neutrinos that early.

    • by Soupster (1242846)

      If neutrinos were faster than c, the neutrinos from SN1987A would have arrived "five years sooner," [newscientist.com] while they were measured arriving "3 hours before the dying star's light caught up" as expected...

      You are making the assumption that the neutrinos from SN1987A were excited to the same or higher energy level by the supernova that the LHC neutrinos were excited to. My bet is this assumption is false.

  • Sorry, but the suggesting that CERN and OPERA clocks are the GPS satellites and adjusting for there speed is just wrong. CERN and OPERA used GPS for accurate geophysics and timing measurement but have they own synchronized clocks in the earths frame. The fasting than light measurement isn't going to go away that easily.

    My personnel solution is that neutrinos feel a fifth force (many at low energy), and this fifth force as left a enough binding energy for the Scarnhorst effect to increase the speed of th

  • bogus (Score:5, Interesting)

    by bcrowell (177657) on Saturday October 15, 2011 @08:10PM (#37726994) Homepage

    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 [nature.com]). 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 [livingreviews.org] 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.

  • Any possible way to setup this experiment as a round-trip, so that only one clock matters?

  • The first thing that I thought of when they announced the FTL Neutrinos was that they did not take into account the relativistic motion in their measurements.

  • by Anonymous Coward on Saturday October 15, 2011 @09:47PM (#37727600)

    "We don't serve faster than light neutrinos here", said the bartender. A neutrino walked into a bar.

  • About 3 weeks ago there was this story http://science.slashdot.org/story/11/09/25/223216/the-mythical-tunnel-between-cern-and-central-italy [slashdot.org]"> where everyone laughed at the Italian minister of Public Education and Scientific Research who issued a press release which congratulated the scientists and mentioned that Italy had funded the construction of a "tunnel between the CERN [in Geneva] and Gran Sasso [the labs in Central Italy]".

    But according to this new article: "scientists created neutrinos at CERN

    • Are you being serious? Neutrinos travel through "solid" matter easily. There's no need for a tunnel, the particles are capable of traveling through the earth.

      I could understand not knowing that the first time the story came up, but it's been awhile now. And if it was intended as a joke, it's gotten stale at this point.
    • by nedlohs (1335013) on Saturday October 15, 2011 @10:32PM (#37727820)

      Through the ground.

      Just like you don't need to remove the air in a "tunnel" between point A and point B to send a beam of light between them, you don't need to remove the rock in a "tunnel" between point A and point B to send a beam of neutrinos between then. Of course enough air will block the light as and several hundred light years of solid rock would block the neutrinos. 900km of rock however is not going to do anything, digging a tunnel would make no difference at all.

    • Easy: quantum tunneling.
  • I don't understand what they are getting at.

    The distance from GPS to earth is different than the distance seen from earth to GPS. This is certainly correct.

    The address this GPS satellites slow their clocks to emulate the passage of time on the ground to correct for existing in an accelerated frame and difference in gravity.

    The author seems to be making some bizzare conclusion since the observed distances are different in each frame the flight time of photons needs further adjustment to account for the diffe

  • The authors have documented their whole procedure here: http://www.ohwr.org/projects/cngs-time-transfer/wiki [ohwr.org] The author of the bogus paper assumes the people who designed GPS and those who use it in metrology labs around the world to manufacture GPS do not know anything about relativity. He also proceeds to an analysis without checking his very basic premises first with the authors of the neutrino velocity paper, or anybody close to the actual experiment. Is it that hard to check one's assumptions first?
  • I know it's tough but to verify, they could put a long fiber optic along the route, and then measure the time of flight of light forwards and backwards.

    If light, using the same measurement system takes the same amount of time West to East as East to West they know there's nothing monkeying with their measurements.

The first version always gets thrown away.

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