Faster-Than-Light Neutrino Puzzle Claimed Solved by Special Relativity
technologyreview.com
technologyreview.com
The scientists probably didn't take this into account because they assumed their setup already compensated for all kinds of clock drift... I wouldn't call this an epic failure just yet, because even if this turns out to be the root cause it's a pretty standard type of mistake as far as science experiments go. That's why we have independent reviews, and that's why they are necessary.
I am seriously doubtful that these neutrinos are traveling faster than light, but I've also been skeptical of this argument since it was presented. It would be pretty hard to have observed this if they weren't looking for it because they would have to sift through old data. For example, for SN 1987A the FTL neutrino event would have preceded the visible light neutrino event by over four years.
They could go through all of the old data, to be sure, but they would have to specifically have had to be looking for something which they think fundamentally is impossible in order to find something like this. So, if these events were even recorded at all, it's certainly not clear to me that they would have done this (at the time of the FTL announcement, that is- of course, they should be doing it now).
it's a pretty standard type of mistake as far as science experiments go
Yes, but when one makes it this far it is big news. No matter what I give props to the scientists to publicly invite the scrutiny they did. That took balls.
So I shouldn't post when I'm annoyed, because then I tend to bark at things that are not what they appear to be.
The GPS system was not remotely designed for this level of accuracy. The issue here could really be a misconception of how well GPS works and what it was designed to do. GPS, like all technology, has a distinct difference between theory and practice and is also engineered for certain use cases. It may be that no one really thought about this stuff until now because we're talking such tiny increments of time over such large distances.
Regardless, its early in the game to know whats going on, but I'd be really surprised if suddenly neutrinos were FTL and no one noticed until sometime this year. This is starting to look like another case of super-smart over-specialized eggheads making assumptions and not seeing the big picture, like when NASA/Lockheed lost the Mars Climate Orbitor over imperial to metric conversions.
What a fucked way to spin this -- the group asked for outside help in explaining their results and finding any mistakes.
Seriously, if you're claiming you're doing FTL, asking for outside help isn't some noble act, its pretty much required. The idea that these guys are infallible and systemic errors never happen is incredibly naive.
Christ, remind me never to get between nerds and their starship Enterprise fantasies.
The GPS receivers they used are form Septentrio, and this guys know their shit. I can't find a reference right now, but if I remember correctly one of their claims to fame is detecting an error in GLONASS, the Russian gps system.
Compensating for special relativity in the timing calculations was a job that had to be done, and done perfectly, long before the first GPS satellite was launched.
My guess is that the bug will indeed turn out to be a relativity issue, but a consequence of GR rather than SR, arising from the fact that the detector cavern is under 1400 meters of rock.
The point to remember that there are so many possible factors that could mess up their results, that the error estimates that were published by the OPERA team were way too low.
This is even less than a trivial application of special relativity, it's literally a third grade "distance = rate x time" problem:
Skipping over the relativistic stuff, which is quite frankly unnecessary (or rather, it's necessary, but the CERN authors apparently already included the corrections), the only two equations of import are (re-named vars for lack of LaTeX):
1) time_baseline = dist_baseline / c
2) time_observed = dist_baseline / (c+v)
where v is the speed of the satellite. In other words, if two things are moving towards each other, then you should use the combined velocity to compute the time. Duhhh...
Now, the fact that the difference in these formulas turns out to almost exactly explain away the problem is certainly suggestive, I'll be honest about that.
But if this was all there was to the story, it would be massively embarrassing for someone at CERN, this is the type of error I mentally ruled out immediately because these people should be way too careful to be making elementary screwups like this. This is the type of error that freshmen lose points for on a mechanics 101 test, not one that eludes dozens of physicists working around the clock for a month.
So I'm skeptical here; it's not that the author of this paper is wrong (though there are credibility red flags in the paper, even beyond the fact that he's not a physicist [he's a computer guy], like the fact that he defines gamma as the inverse of the commonly used relativistic quantity, something that indicates only a passing familiarity with the field), it's that I'm not sure that the CERN guys could reasonably be assumed to have made this mistake.
Then again, maybe everyone else looking over the work also assumed that they'd dotted their i's, and didn't bother checking the trivial stuff. It's certainly happened before...
I understand the difference in frames between the GPS satellites and the ground, but the sats themselves are fixed to each other, right? And the ground stations are also fixed to each other. Each pair is in a separate frame.
But the measurement was on the ground, and the ground stations are not accelerating relative to each other, not from the satellites. So is this saying that the ground stations set their clocks initially wrong because of their relative movement to the satellites? If so, wouldn't this be proven out by comparing the neutrinos time to the time of a photon?
it is compare to zero gravitation far from Earth. The effect i'm talking about is integral of gravitational dilation change along the path of neutrinos. This path is a chord under Earth surface - the 350 km down to 10km depth and the next 350km bringing back to surface. The dilation change is about 1e-16 per meter of depth.
Actually, the satellites and ground stations are accelerating relative to each other, since they're moving in(roughly) circular paths. Acceleration only means that the velocity vector is changing relative to the frame of reference. It doesn't mean that the absolute velocity is changing.
The problem is that the GPS satellites are the ones keeping time, not the ground. The ground stations are effectively "reading" the clocks on the satellites. So all of the relativistic time calculations should be done from the satellites' frame of reference, rather than from the ground stations' frame. The satellites are moving from west to east(with the Earth's rotation) with an orbital period of approximately 12 hours(http://en.wikipedia.org/wiki/Satellite_navigation#Comparison...). Their rotational velocity, relative to the center of the Earth, is twice that of the ground stations. In terms of absolute velocity, they're moving quite a bit faster. Since they are doing the timekeeping(and assuming that neutrinos move at c regardless of the frame of reference), the receiving ground station is moving towards the initial origin point of the neutrino stream. At that point, it's a doppler effect calculation taking into account the relative velocity of the ground stations to the satellite's frame of reference to find the offset.
Also, the photon time measurement isn't possible due to the curvature of the Earth and the fact that the receiving end is underground.
Whoa, why would you think that? GPS satellites are in 12-hr, medium-earth, circular orbits in six-orbital planes. How would satellites in different orbital planes maintain fixed distances from each other?
In reality it's more complicated, since there is no one "satellite" frame. The GPS system determines position and receiver time from a global solution to all the satellites. Since GPS time is claimed to be accurate to something like 10ns, it seems the only way this would be possible is if the GPS solution has been constructed to specifically refer the frame of the observer, which would be a ground stationary frame.
Is there someone with more intimate knowledge of the GPS algorithm that might be able to comment on this?
First off, I encourage everyone to read the actual paper at 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) 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.
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.
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?
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
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.
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.
Even if the satellite is swallowed by a black hole, that measurement frame still exists as an abstract concept.
Unfortunately I don't think it matches up with what CERN did in reality, which is synchronize clocks in the ground frame.
Time = Distance / Velocity
Time_EarthCenterFrame = Distance_EarthCenterFrame / Velocity_EarthCenterFrame
Time_LaboratoryFrame = Distance_LaboratoryFrame / Velocity_LaboratoryFrame
Time_SateliteFrame = Distance_SateliteFrame / Velocity_SateliteFrame
Time_SateliteFrame ¿=? Distance_ LaboratoryFrame / Velocity_EarthCenter :(
v_tot = c + v
v_tot = (c + v)/(1+ cv/c^2) = (c + v)/(1+ v/c) = c* (c + v)/ (c+ v) = c
(Really, the SateliteFrame, LaboratoryFrame and EarthCenterFrame are not inertial frames, but this is another kind of problem.)
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.
From what I can tell, the quoted passage, "From the perspective of the clock, the detector is moving towards the source and consequently the distance travelled by the particles as observed from the clock is shorter," is the core of the argument. I think this is what you need to consider/read into it:
- There is relative rotation involved, so the frames are accelerating with respect to each other.
- Since the times involved are very short with respect to the period of rotation, we can probably ignore the acceleration itself (?), BUT:
- LHC and GS have differing velocity vectors at any given time due to their difference in longitude. This means we have to treat them as separate frames of reference. ("From the perspective of the clock, the detector is moving towards the source")
- I think this is just about a single satellite (though since the satellites are in orbit, they too are accelerating wrt earth)
- I'm not sure if the effect will vary slightly depending on the satellite's position, but as it has to be "visible" from both locations, the range of possible positions is fairly constrained. I'd have to work it through/read the paper. :-P
And yeah, comparing to the time of a photon is going to be difficult through the earth. Even gamma radiation won't make it.
so instead of comparing to photon going through the fiber on the surface we're comparing against photon(s) going to the satellite and back. Even just using HAM radio bouncing from ionosphere would be less complicated and more straightforward than through GPS satellites here.
2. The distance traveled by radio waves bouncing off the ionosphere would have much more uncertainty than the ~60 feet in question.
3. Radio waves in the air and photons in a fiber will move noticeably slower than c due to the fact that they are not traveling through a vacuum. Neutrinos, however, minimally interact with matter, so they would travel faster than the test photon(s).
it is still shorter than through the satellite. Also the fiber distance difference can be measured and accounted for - much simpler than to account for satellite position.
by noting photons coming from GPS when neutrinos start at CERN and when neutrinos reach Gran Sasso. 2 downward legs (actually 3 as the photons at the start of neutrino run need to be noted at both points) instead of 1 upward and 1 downward that would constitute proper "bouncing" - i don't see much difference to warrant specific term in this case than talking about general approach of racing the neutrinos against photons.
Compare to running through a fiber, which length (only 700km) and speed of light inside it can be easily accounted for, with GPS we have photons coming from the 12K miles distance (in the best case, ie. when the satellite is right overhead) which is measurable much less precisely than the fiber on the ground and these photons are coming through the atmosphere conditions of which (specifically speed of light in it) are much less precisely known than about the same fiber on the ground.
>and measuring the distance, which is accurate to a lot less than the distance light travels in 60ns.
until they used the military GPS they would have positioning error in the Earth surface tangential plane of a few feet at least (say 2 feet though it would be an extremely small error). Using 20000km/700km proportionality of that triangle, 2 feet on tangential plane would mean ~60 feet in GPS signal arrival precision, ie. 60ns+ of time of flight (it is of course oversimplification, only to demonstrate the scale of imprecision inherently present in the scheme with satellite flying over at 20K km)
Very interesting reading btw, especially on atmospheric and Stagnac effect errors :
http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_P...
"The engineers who designed the GPS system included these relativistic effects when they designed and deployed the system. ... Further, each GPS receiver has built into it a microcomputer that (among other things) performs the necessary relativistic calculations when determining the user's location." [1]
[1] http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps....
It can't compensate for the effect in the linked-to article (namely, the fact that the distance and flight time between the neutrino source and destination is shorter according to the satellite, versus an observer on the ground) because that effect depends on the specifics of the experiment.
Consider this: If you flipped the location of the neutrino source and destination, you'd actually get the reverse effect (neutrinos would appear to be going slower than light).
So it's up to observers on the ground to compensate for relativistic effects of this nature.
(As I mentioned in another comment, I would be shocked if they didn't already do that)
Also, GPS satilites don't orbit in one direction you need 3 to quickly get an accurate posisiton so they use a wide range of orbits to minimize the number needed. http://www8.garmin.com/aboutGPS/ Which is something the article seems to miss.
2) They all orbit in the same direction.
3) There are a number of different orbits, but they are all inclined at the same angle.
The illustration on that page was, I'm afraid, drawn by someone with no clue what the constellation actually looks like.
2) They all have polar orbits that reach the same location 4 minutes earlyer each day. However, there horizontal ground speed relative to a stationary observer changes over the course of their orbit. (It's zero at the pole and maxes out at the equator.) And is also diffrent form the other satilites you are comparing it with.
Which is why you get those S shaped paths: http://www.n2yo.com/satellites/?c=20
3)I agree but see 2.
PS: Yea, that picture was fairly bad, I was looking for an easy to read article not a picture. The classic picture of a constilation with fixed polar obits is vary misleading once you take the earth's rotation into consideration. It's rare to find something that shows both the orbit's and their horisontal velocity fairly accuratly without making it look like they interweave. I once saw an animation showing the orbit of 4 satilites and the area they could cover area just those 4 satilites could give you coverage of but it's far harder with just a picture.
None of the satellites are in a polar orbit. The orbits are inclined at 55° to the equatorial plane.
Now suppose P1, P2, P3 velocity is more than 2x that of point U and you have you have new offsets from U to {P1,P2,P3} you are now going to have a new curve (c2) in 3d space, but you know U's vector must take it from c1 to c2.
Now add another time cycle, and you know it's vector must take it from C1 to C2 to C3. As you keep adding C's you constrain both the valid vectors(direction and velocity) as well as positions.
Now measurement accuracy as well as change in velocity limit the accuracy but GPS satellites are moving a lot faster than you are so you can get reasonably accurate information this way. Edit: Also you can basically ignore the sections of the curve that whose altitude is unreasonable so the solution space is fairly constrained to start with and for each subsequent curve. But you can also use an internal clock/oscillator, accelerometer, gyroscope to further constrain reasonable accelerations etc.
I agree on the other points. They all have an inclination of 55° in regard to the equator. See Wikipedia [1] for details and a more serious illustration
You would need three if you had an atomic clock: if you knew the precise time. But in practice you do not. You have a good clock that has an unknown shift with respect to the clocks in the satellites.
So you can measure differences in times, but not absolute times. I.e. you do not know the distance from the gps to the satellites, you know the difference of these distances. So you need a fourth satellite.
This was designed because it is easy to make accurate relative time measurements, but hard to have an absolute time reference.
Don’t forget we have a lot more CPU to throw at these problems than they did in 1980.
I was impressed that they allow for continental drift in their analysis and indeed that they were apparently able to detect the crusts movement by an Earthquake with the apparatus.
>Consider this: If you flipped the location of the neutrino source and destination, you'd actually get the reverse effect (neutrinos would appear to be going slower than light). //
Flipped WRT what? They've run the experiment at differing times of the day when the experiment is effectively flipped WRT the helios.
They also present a tentative energy relationship with the apparent superluminal speed which wouldn't, it seems, be accounted for by a simple relativistic [time-shift] systematic uncertainty.
It's "flipped" only with respect to the center of the earth. Since this isn't a point of measurement(the satellites are the ones effectively holding the stopwatch), it's not really worth taking into account.
If the neutrino stream was going west->east(i.e. with the satellites) rather than east->west, the receiving station would appear to be moving away from the starting point of the neutrino stream. That would effectively decrease the speed of neutrinos.
The authors of the OPERA paper [5] seem to include a correction for the Lorentz transformations, but they not correct for the change in scenario. And because they project back the time of provided by the moving clock to the baseline they seem to incorrectly assume that the outcome of their experiment should be equivalent to that using a clock in the baseline reference system
I am a Frenchman living in the Netherlands. And you are both correct and incorrect ...
The Dutch are probably among the most fluent non-native English speakers in Europe, BUT, they speak for most of them a "good enough" English, and not at all a perfect English.
This usually materializes even more when they are writing. There is even several books (usually written by Dutch authors themselves) making fun of "dutchisms".
That said, I don't necessarily consider myself better ... Simply, I do other kind of mistakes, so their mistakes usually strike me more than my own mistakes of course, but mistakes of other French speakers as well
There will be no flurry of HN links about this when someone replicates it (even assuming, for the sake of argument, that neutrinos really can be fired FTL, all of current physics is wrong, etc etc). Maybe a single link. It just won't have the network effect; too much of the collective audience's interest has already been consumed. And there'll definitely be no HN links when the third and fourth teams replicate it.
Even if that's a wrong claim for this hypothetical result about relativity, consider yesterday's "forced exercise and Parkinson's" link ( http://news.ycombinator.com/item?id=3106799 ). That result is _completely_ immature (the rat experiments tested something very different from the human experiments, there has only been one human experiment, the causal story is all conjecture, etc), and there's no _way_ we're gonna hear about it when it's usefully mature (i.e. after ten more studies). (Epistemologically, I think the current result is not far removed from alternative medicine - there's some evidence, but no elegant pattern of evidence across multiple contexts, and no rigorous-but-failed attempts at falsification.) It's an interesting subject, and an interesting research programme, and I want to know about things like this, but it's too early to take this into account when making lifestyle tradeoffs.
So it seems to me that my choices are kind of ugly: I can read a LOT of cutting-edge stuff, and read all the follow-ups, knowing that most of the ground-shakers won't actually pan out. Or I can wait 20 or 50 or more years until it starts showing up in undergraduate textbooks. Or... I don't know, there must be other options, but I don't know what they are. Another option is reading Malcolm Gladwell et al, which I think is generally viewed with a certain exasperation by the genuinely knowledgeable?
Is there a blog or magazine or whatever, that popularizes science, with this slightly delayed view? "Exciting science news from 10 years ago, complete with a decade of 20/20 hindsight!"
So, how did that story with the solar panels made from hair pan out? It was pretty solidly debunked here on HN (as it rightly should have been), but what interests me is what happened to the major players in that episode, if they're still making solar panels from hair or if they came to terms with their error and documented that and published it to negate some of the damage done.
Interestingly, the paper also states ('Missing Relativity Terms?', pp. 195-197) that there has been confusion in the past caused by people thinking the time is measured in the ECI frame. It shows that the uncorrected-for relativistic effects have an error on the order of only 2-3mm for a stationary observer on the earth's surface (the same is not true for e.g. other satellites). 'In short, there are no "missing relativity terms."'
There are obvious things to correct for -- e.g. if you're standing at the finish line the sound from the finish line will take 1/3 of a second (roughly) to get to you, so you need to adjust your calculation.
Now suppose that you are standing off on a barge during the race. You know the distance to the start and finish lines but ignored the drift of the barge because you figured it was insignificant.
We're talking 60 nanoseconds. The satellites are moving at tens of thousands of miles an hour.