5 ms·

I'm super-skeptical about this paper - I agree that more info on the GPS stuff is needed (this author seems to be making assumptions about how the correction pr

I'm super-skeptical about this paper - I agree that more info on the GPS stuff is needed (this author seems to be making assumptions about how the correction procedures work that I couldn't find documentation for), but on its face, this just seems way like a way too obvious error to possibly be right. First off, I encourage everyone to read the actual paper at http://arxiv.org/pdf/1110.2685v1 http://arxiv.org/pdf/1110.2685v1 [PDF], I think many here are seriously overestimating the complexity of the author's claim. I've mostly said this already on this thread, but it's buried near the bottom of the page, so I'll summarize the paper here, it's extremely simple: 0) If you're measuring time in the reference frame of the moving clock, you've got to transform the length between the stations in accord with the Lorentz transformation. According to this author CERN already did this, so it's entirely irrelevant to the discussion - I couldn't verify this, because it's not mentioned in the CERN paper he referenced. 1) What they did not do (according to this paper) is account for the fact that in the satellite frame, during the neutrino's flight the receiver station was moving towards the source. 2) time = distance / rate 3) CERN used rate = c, but they should have used rate = c + v because the receiver station was moving towards the neutrino. That is quite literally the entire thing, check the math in the paper if you don't believe me. This is not a claim that CERN somehow misapplied special relativity, it's a claim that they simply forgot to include the motion of the receiver. IMO this is far too elementary a mistake to have been missed for this long, so I'm suspicious. The CERN paper that the author references (http://arxiv.org/pdf/1109.4897v1 http://arxiv.org/pdf/1109.4897v1) doesn't discuss relativistic corrections at all, so I don't know why the author assumes this mistake has been made, perhaps he's reading another paper that he didn't reference? From the OPERA one that he links (though I haven't read it in too much detail) I get the sense that if it was this simple, one of the many calibration tests that they've done would have easily caught the error (they talk about a lot of bidirectional synchronization stuff), so for now, at least, I would take this with a grain of salt.

bermanoid 15y ago
Also worth noting, DanielBMarkham's comment is spot on, from what I read in the OPERA paper, the clocks in question are indeed not on the satellites, they're just synchronized using the satellites, and then that synchronization is tested extensively on the ground. So the time measurements should not depend on the satellite frame at all, by my understanding.
- lutorm 15y ago
  then that synchronization is tested extensively on the ground Not possible. There is no way to test whether the clocks are synchronized. If they could "check" the synchronization by any other, more accurate, source then that should have been the reference.
  - DanielBMarkham 15y ago
    So the clocks were set incorrectly. Then I'm left with just being confused about frames. How is it that the satellites slow one result and not the other? Assuming for simplicity you are using one satellite, it would have to be directly between the test sites in order for this to happen, right? If the satellite is approaching both sites, or if it is leaving both sites, the changes would affect both sites equally. I'm not following how the general east-west orbits of the satellites have anything to do with anything. The only thing that's important is the relative motion between the satellites and each station. Both should be affected the same way I would think. No?
    - bermanoid 15y ago
      First off, let me reiterate that I don't believe that the objection in this paper is likely valid, because I don't think the CERN scientists were actually measuring anything from the satellite frame. Buuuuut... Assuming for simplicity you are using one satellite, it would have to be directly between the test sites in order for this to happen, right? If the satellite is approaching both sites, or if it is leaving both sites, the changes would affect both sites equally. I think I can explain this - first, the position of the satellite is not important to this argument, it's only the velocity that matters. Here's what we need to assume, for the purposes of pretending that the paper has a valid objection: we figure out what the clock on the satellite says at the moment that the neutrino leaves station A (this requires some computation, because it takes time for light to travel, etc. - don't sweat that, we assume we're calculating this after the fact, and can pinpoint the exact moment it leaves). Then we figure out what the clock on the satellite says when the neutrino hits station B. From the point of view of the satellite, here's a picture of the way everything is moving: <-A neutrino-----> <-B A and B are moving to the left with velocity v, and the neutrino is (we assume) moving to the right with velocity c. The distance from A to B is L, as observed by the satellite (ignore whatever length contraction stuff you're tempted to think of - we're in the satellite frame, now and forever). Now, the author here is arguing that CERN calculated the theoretical time of transit for this situation as delta_t_wrong = L / c and then expressed surprise when the measured value was less than that. But that's clearly a wrong formula - station B is moving to the left as the neutrino moves to the right, so the true time that they meet is delta_t_correct = L / (v + c). Notice that it doesn't matter where the satellite is, we're just looking at the relative velocities from the perspective of the satellite. If it was orbiting the other direction, then the error would be that it looked like it took too long. [If it bothers you that no matter what the speed of the satellite the speed of the neutrino is always c, then hello relativity!, that's another story for another day] I should point out that this would be a completely valid complaint if CERN actually was calculating things this way and getting measurements from the satellite's inertial frame. But I don't think they are, I'm pretty sure all of their time measurements come from the ground clocks, in which case there's no time-of-transit shenanigans to be monkeyed with.
lutorm 15y ago
What they did not do (according to this paper) is account for the fact that in the satellite frame, during the neutrino's flight the receiver station was moving towards the source. That can not possibly have an effect. The clocks are synchronized before the experiment. Once the synchronization is done, the satellite could be swallowed by a black hole and it would not affect the measurement.
- caf 15y ago
  I believe the idea is that the clocks are synchronised in the frame of the satellite. Due to the relativity of simultaneity, it doesn't make sense to talk about the clocks being synchronised in an absolute sense. Even if the satellite is swallowed by a black hole, that measurement frame still exists as an abstract concept.
  - bermanoid 15y ago
    I believe you're right, that's basically what this paper suggests. Unfortunately I don't think it matches up with what CERN did in reality, which is synchronize clocks in the ground frame.
    - caf 15y ago
      Is there even a single "ground frame" here? The two laboratories are in relative motion.
      - lutorm 15y ago
        What you say is true, but that motion is small compared to the motion of the satellites in relation to either of the ground stations.
  - lutorm 15y ago
    Oh, I think I misunderstood the statement. They original quote must mean receiver and source of neutrinos. Somehow I read it as being the GPS source and receiver, in which case it doesn't make sense.
gus_massa 15y ago
When using special relativity it is extremely important to understand which inertial frame you are using. So the in the formula Time = Distance / Velocity you must explicitly say in which frame you are measuring the things. It could be Time_EarthCenterFrame = Distance_EarthCenterFrame / Velocity_EarthCenterFrame Time_LaboratoryFrame = Distance_LaboratoryFrame / Velocity_LaboratoryFrame Time_SateliteFrame = Distance_SateliteFrame / Velocity_SateliteFrame and it is usualy not a good idea to mix the frames like Time_SateliteFrame ¿=? Distance_ LaboratoryFrame / Velocity_EarthCenter :( In the same way, it is not a good idea to add the velocities classically with v_tot = c + v you should use the relativistic correction v_tot = (c + v)/(1+ cv/c^2) = (c + v)/(1+ v/c) = c* (c + v)/ (c+ v) = c so in every inertial frame the speed of light is the same. (Really, the SateliteFrame, LaboratoryFrame and EarthCenterFrame are not inertial frames, but this is another kind of problem.)
- bermanoid 15y ago
  Actually, in this case the classical velocity addition formula is the correct one to use - the formula you mention applies to a moving reference frame, but the author's objection was that in the satellite frame the CERN folks mis-calculated the time it would take for a neutron moving to the right to meet up with a station moving to the left. This is why to call this a relativistic objection is giving it far too much credit: the author is, quite literally, claiming that the physicists at CERN don't know how to solve a purely classical rate problem.

bermanoid 15y ago

Also worth noting, DanielBMarkham's comment is spot on, from what I read in the OPERA paper, the clocks in question are indeed not on the satellites, they're just synchronized using the satellites, and then that synchronization is tested extensively on the ground. So the time measurements should not depend on the satellite frame at all, by my understanding.

lutorm 15y ago
then that synchronization is tested extensively on the ground Not possible. There is no way to test whether the clocks are synchronized. If they could "check" the synchronization by any other, more accurate, source then that should have been the reference.
- DanielBMarkham 15y ago
  So the clocks were set incorrectly. Then I'm left with just being confused about frames. How is it that the satellites slow one result and not the other? Assuming for simplicity you are using one satellite, it would have to be directly between the test sites in order for this to happen, right? If the satellite is approaching both sites, or if it is leaving both sites, the changes would affect both sites equally. I'm not following how the general east-west orbits of the satellites have anything to do with anything. The only thing that's important is the relative motion between the satellites and each station. Both should be affected the same way I would think. No?
  - bermanoid 15y ago
    First off, let me reiterate that I don't believe that the objection in this paper is likely valid, because I don't think the CERN scientists were actually measuring anything from the satellite frame. Buuuuut... Assuming for simplicity you are using one satellite, it would have to be directly between the test sites in order for this to happen, right? If the satellite is approaching both sites, or if it is leaving both sites, the changes would affect both sites equally. I think I can explain this - first, the position of the satellite is not important to this argument, it's only the velocity that matters. Here's what we need to assume, for the purposes of pretending that the paper has a valid objection: we figure out what the clock on the satellite says at the moment that the neutrino leaves station A (this requires some computation, because it takes time for light to travel, etc. - don't sweat that, we assume we're calculating this after the fact, and can pinpoint the exact moment it leaves). Then we figure out what the clock on the satellite says when the neutrino hits station B. From the point of view of the satellite, here's a picture of the way everything is moving: <-A neutrino-----> <-B A and B are moving to the left with velocity v, and the neutrino is (we assume) moving to the right with velocity c. The distance from A to B is L, as observed by the satellite (ignore whatever length contraction stuff you're tempted to think of - we're in the satellite frame, now and forever). Now, the author here is arguing that CERN calculated the theoretical time of transit for this situation as delta_t_wrong = L / c and then expressed surprise when the measured value was less than that. But that's clearly a wrong formula - station B is moving to the left as the neutrino moves to the right, so the true time that they meet is delta_t_correct = L / (v + c). Notice that it doesn't matter where the satellite is, we're just looking at the relative velocities from the perspective of the satellite. If it was orbiting the other direction, then the error would be that it looked like it took too long. [If it bothers you that no matter what the speed of the satellite the speed of the neutrino is always c, then hello relativity!, that's another story for another day] I should point out that this would be a completely valid complaint if CERN actually was calculating things this way and getting measurements from the satellite's inertial frame. But I don't think they are, I'm pretty sure all of their time measurements come from the ground clocks, in which case there's no time-of-transit shenanigans to be monkeyed with.

lutorm 15y ago

What they did not do (according to this paper) is account for the fact that in the satellite frame, during the neutrino's flight the receiver station was moving towards the source. That can not possibly have an effect. The clocks are synchronized before the experiment. Once the synchronization is done, the satellite could be swallowed by a black hole and it would not affect the measurement.

caf 15y ago
I believe the idea is that the clocks are synchronised in the frame of the satellite. Due to the relativity of simultaneity, it doesn't make sense to talk about the clocks being synchronised in an absolute sense. Even if the satellite is swallowed by a black hole, that measurement frame still exists as an abstract concept.
- bermanoid 15y ago
  I believe you're right, that's basically what this paper suggests. Unfortunately I don't think it matches up with what CERN did in reality, which is synchronize clocks in the ground frame.
  - caf 15y ago
    Is there even a single "ground frame" here? The two laboratories are in relative motion.
    - lutorm 15y ago
      What you say is true, but that motion is small compared to the motion of the satellites in relation to either of the ground stations.
- lutorm 15y ago
  Oh, I think I misunderstood the statement. They original quote must mean receiver and source of neutrinos. Somehow I read it as being the GPS source and receiver, in which case it doesn't make sense.

gus_massa 15y ago

When using special relativity it is extremely important to understand which inertial frame you are using. So the in the formula Time = Distance / Velocity you must explicitly say in which frame you are measuring the things. It could be Time_EarthCenterFrame = Distance_EarthCenterFrame / Velocity_EarthCenterFrame Time_LaboratoryFrame = Distance_LaboratoryFrame / Velocity_LaboratoryFrame Time_SateliteFrame = Distance_SateliteFrame / Velocity_SateliteFrame and it is usualy not a good idea to mix the frames like Time_SateliteFrame ¿=? Distance_ LaboratoryFrame / Velocity_EarthCenter :( In the same way, it is not a good idea to add the velocities classically with v_tot = c + v you should use the relativistic correction v_tot = (c + v)/(1+ cv/c^2) = (c + v)/(1+ v/c) = c* (c + v)/ (c+ v) = c so in every inertial frame the speed of light is the same. (Really, the SateliteFrame, LaboratoryFrame and EarthCenterFrame are not inertial frames, but this is another kind of problem.)

bermanoid 15y ago
Actually, in this case the classical velocity addition formula is the correct one to use - the formula you mention applies to a moving reference frame, but the author's objection was that in the satellite frame the CERN folks mis-calculated the time it would take for a neutron moving to the right to meet up with a station moving to the left. This is why to call this a relativistic objection is giving it far too much credit: the author is, quite literally, claiming that the physicists at CERN don't know how to solve a purely classical rate problem.