This is an almost trivial application of special relativity. It was be absolutely shocking if the dozens of scientists involves in the neutrino experiment didn't take this into account.
I'd file this under "systematic measurement error", and the team specifically said that something like it was the most likely cause for the results. They also said that if neutrinos really were FTL, we'd have observed this effect much earlier (for example when we started measuring supernova radiation bursts). So, the article's hypothesis is a very good candidate for a real flaw in the experiment's design.
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.
"Almost trivial"? You're vastly exaggerating. I'm pretty sure most physics graduates would get problems of special relativity as applied to rotating (i.e. accelerating) systems completely wrong, as it's usually just not taught. Yep, someone doing the experiment should have ideally spotted it, but it's already an extremely complex system, so I'm not surprised they didn't.
They obviously did take all kinds of relativistic effects into account. It's not like they forgot about relativity. It's just that they may have overlooked a higher-order effect that is usually neglected because it is so small. Something like overlooking magnetism when looking at electricity (magnetism is a relativistic effect of moving electrical charge, but since the forces involved are so small, they are easy to miss and neglect)
That's what I was thinking too- this may be destined to become a problem in a relativity class (perhaps a little above Modern Physics, though). But then maybe I don't fully understand the subtleties.
This is an almost trivial application of special relativity.
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...
my thoughts exactly - my guess is that the editor wanted to point out this potential source of an error, because his readers were likely to understand it. to me the error seems to be too trivial for an experiment of that magnitude.
How many of these guys are GPS satellite engineers? It sounds like they falsely assumed that the GPS system would take care of all relativistic effects and they can just use absolute time for measurement.
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.
Okay. This should be an easy one but somehow I'm getting stumped.
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?
I think this is the issue: The time is given by the GPS satellites sending out a signal. This signal is received by the two ground stations, who reset their time accordingly. This means that the two ground station clocks will define two events as simultaneous in the frame of the satellite. But the measurement is done in the ground frame. Two events that are simultaneous in the satellite frame are not simultaneous in the ground frame, due to the relative motion of the two frames. In the ground frame, there will be an offset between the two clocks, and that would, unless corrected for, result in a skewed measurement of the time of flight.
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?
>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? If so, wouldn't this be proven out by comparing the neutrinos time to the time of a photon?
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.
Disclaimer: It's been a few years since uni, and I haven't read the actual paper, just the linked article.
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.
> but the sats themselves are fixed to each other, right?
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?
The neutrino is going through the earth - there's no tunnel - so there's no way to compare to a photon. Basically Gran Sasso is moving towards the neutrino as it travels, from the perspective of the GPS
I haven't read the article yet. However, the ground stations are deeper in the Earth's gravity well than the satellites. That is equivalent to acceleration in relativity.
But the GPS satellites and receivers already correct for these relativistic effects. Specifically:
"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]
Relativistic effects are only taken into account when determining the position of the satellite itself, and the rate of it's clock.
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)
I think it's more subtle than that - it's due to the motion of the satellites relative to the experiment (i.e. the direction of the neutrino path), not to the individual ground stations
If true, this just goes to show how many effects you need to take into account when dealing with numbers that are 2 thousands of a percent. Effects that can normally be ignored because they're in the noise, turn out to be in the signal instead.
Until the faster than light result can be recreated in an independent experiment, I am treating this like cold fusion. Neat result and absolutely deserving of further investigation, but not definitive.
I don't really get why you're being downvoted to oblivion, that's a great stance to take on science in general. So much media buzz is made over n=1 things; you can cut out a lot from your information diet by ignoring things until they get replication. If special relativity is wrong, we'll find out in due course, and the current counter-evidence against special relativity is hardly a dent compared to the massive evidence in favor (both theoretical and experimental). Just a few days ago I discovered this paper: http://arxiv.org/abs/1005.4172 They assert Events as the only fundamental object, not space, not time. Then: "by asserting that some events have the potential to be influenced by other events, but that this potential is not reciprocal, we can describe the set of all events as a partially ordered set or poset, which is typically known as a causal set" and from there they derive Special Relativity.
This paper: http://tycho.usno.navy.mil/ptti/1996/Vol%2028_16.pdf
states that "the time rate is appropriate to observers on the surface of the rotating earth, that is, in the ECEF". I'm interpreting that to mean that the issue raised in the OP is not correct, but I am by no means an expert in relativity.
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."'
They do, and they used a mobile atomic clock to compare the times. The problem is that both locations are in different, accelerated frames of reference, so reasoning about time in those frames of reference can become non-trivial.
could someone please explain this, i wish i could say i get it, but i am so confused. i don't understand, are they not using gps just to synchronize the clocks on both ends? what does it matter if in orbit the distance seems shorter or longer if observed (viewed) from the satellites (is this what they are saying?)?
The simplest way I can (try to) understand it is to imagine a line drawn between CERN and Gran Sasso. From the GPS point of view(consider the GPS satellites as stationary), this line is moving approximately in a Gran Sasso->CERN direction, and is therefore very slightly shorter than what the researchers on the ground calculated
Let's suppose you're trying to time a 100 yard dash based on sound. Someone fires a gun, the race starts, and when the first runner crosses the finish line another gun is fired, you determine the elapsed time.
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.
"Fools", he mutters under his breath, "Neutrinos flying faster than light... I pity your indolence." With wiry fingers he taps his pipe on his knuckles, flinging burnt tobacco beyond the edges of the cloud. "Ah well," he sighs, connecting his iPhone to his Macbook Air, "time to install iOS 5. I bet those servers are not running as red hot any longer".
[+] [-] thegrossman|14 years ago|reply
[+] [-] Udo|14 years ago|reply
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.
[+] [-] pmjordan|14 years ago|reply
[+] [-] gruen|14 years ago|reply
[+] [-] Confusion|14 years ago|reply
[+] [-] dhimes|14 years ago|reply
[+] [-] bermanoid|14 years ago|reply
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...
[+] [-] unknown|14 years ago|reply
[deleted]
[+] [-] jcfrei|14 years ago|reply
[+] [-] drzaiusapelord|14 years ago|reply
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.
[+] [-] DanielBMarkham|14 years ago|reply
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?
[+] [-] lutorm|14 years ago|reply
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?
[+] [-] cube13|14 years ago|reply
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.
[+] [-] pmjordan|14 years ago|reply
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.
[+] [-] dmm|14 years ago|reply
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?
[+] [-] themgt|14 years ago|reply
[+] [-] InclinedPlane|14 years ago|reply
[+] [-] kiwidrew|14 years ago|reply
"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....
[+] [-] thegrossman|14 years ago|reply
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)
[+] [-] themgt|14 years ago|reply
[+] [-] martincmartin|14 years ago|reply
[+] [-] jasondavies|14 years ago|reply
[+] [-] qntm|14 years ago|reply
[+] [-] daimyoyo|14 years ago|reply
[+] [-] Jach|14 years ago|reply
[+] [-] zb|14 years ago|reply
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."'
[+] [-] alain94040|14 years ago|reply
[+] [-] sp332|14 years ago|reply
[+] [-] ck2|14 years ago|reply
[+] [-] perlgeek|14 years ago|reply
[+] [-] macaroni|14 years ago|reply
[+] [-] themgt|14 years ago|reply
[+] [-] podperson|14 years ago|reply
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.
[+] [-] martinkallstrom|14 years ago|reply
[+] [-] martinkallstrom|14 years ago|reply
[+] [-] unknown|14 years ago|reply
[deleted]
[+] [-] crizCraig|14 years ago|reply