CERN team claims measurement of neutrino speed >c


by turbo
Tags: anisotropy, cern, ftl, gps, new math books
Vanadium 50
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Sep25-11, 10:26 AM
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First, a lot of the issues people (especially first time posters) are bringing up are addressed in the paper. Read it. There are very few people who can tell what another group did wrong without knowing what they did.

Second, the difference between a rotating earth frame and a stationary frame is essentially irrelevant. If you draw the space-time diagram for the setup, including
the GPS satellites (one is enough if you assume it's already synchronized) you will discover what they are measuring is very close to the interval between emission and detection, which is a Lorentz invariant. There are two corrections that need to be applied - one is the fact that LGNS is moving 50mph faster than CERN because of the earth's rotation: that's a 10-15 effect. The other is that the earth has moved between the emission and detection times by a few feet. That should be properly taken into account by the GPS receiver (and I have questioned this), and if it is, it's a 10-6 effect on the 10-5 effect, or 10-11.

As I have said before, the application of using GPS to synchronize two distant stations to a nanosecond is not common, and as such I am less confident that the firmware in the unit is bug-free than had the application been more widely used.

Third, the statistical techniques for determining whether Model A or Model B fit the data better (say a 0ns offset and a -60 ns offset) are almost a century old, and well-described in the paper, and shown clearly in Figure 8. The idea that some people here can do a better job with the statistics in their heads is ridiculous.

In any event, Figure 12 makes it clear - this is not a simple statistical fluke: if you moved the data 1.2 bins to the left or right, you would see the difference.
vanesch
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Sep25-11, 11:31 AM
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Quote Quote by D H View Post
Surely, it is. Maybe I didn't communicate it right. vanesch remarked that "clocks at the poles don't suffer any time dilatation as their velocity wrt the inertial frame is 0, while clocks at the equator which have a significant velocity suffer a dilatation." vanesch forgot about general relativistic effects. The net effect is that clocks at sea level (better: clocks on the geoid) tick at the same rate.
Right. I stand corrected. I didn't realize that the GR effect was important here, as Vanadium stated that gravitational effects account for something like 10^-10 and I took that for granted.

However, SR effects account for about 10^-6 (relative velocities), so if what you say is correct, this means that GR effects are also of the order of 10^-6 for a depth of 20 something km. Now, the chord of a 700 km arc dips about 10 km deep into the earth, so one would expect then a similar GR correction to the interval.
f95toli
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Sep25-11, 11:43 AM
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Quote Quote by Vanadium 50 View Post

As I have said before, the application of using GPS to synchronize two distant stations to a nanosecond is not common, and as such I am less confident that the firmware in the unit is bug-free than had the application been more widely used.
I'd say it is very common. GPS is one of two systems used for time transfer in the UTC itself meaning this is done routinely. Granted, it is the less accurate system, but the reason they used in here is presumably because it is good enough. Note that their clocks were calibrated by PTB and METAS and checked by movable time transfer. Hence, I think we can be pretty sure that someone would have told them if they were doing something wrong.
DaleSpam
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Sep25-11, 11:45 AM
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Quote Quote by vanesch View Post
Mmm, but how come then that they find agreement with a land-based survey, which measures in the rotating frame, as they say, in the paper ?
The differences in distance Between the land based and gps surveys is several orders of magnitude too small.
PeterDonis
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Sep25-11, 11:57 AM
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Quote Quote by neopolitan View Post
I'm just not sure that there is a general acceptance that a path which passes through a region of (albeit slightly) lower gravitational potential might be shorter than the calculated distance between two points on the surface of geoid.
Whatever effect there might or might not be from this, it is way too small to matter. See post #177; at most a change in path length due to the change in gravitational potential would be about a 10^-10 effect.
PAllen
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Sep25-11, 11:59 AM
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Quote Quote by vanesch View Post
Right. I stand corrected. I didn't realize that the GR effect was important here, as Vanadium stated that gravitational effects account for something like 10^-10 and I took that for granted.

However, SR effects account for about 10^-6 (relative velocities), so if what you say is correct, this means that GR effects are also of the order of 10^-6 for a depth of 20 something km. Now, the chord of a 700 km arc dips about 10 km deep into the earth, so one would expect then a similar GR correction to the interval.
How do you get the SR effect you claim? For gamma to differ from 1 by 1 part in 10^7, I get a required relative speed of 83 miles per second. For a relative speed of 1000 mph, gamma differs from 1 by 1 part in 10^12 or so.
vanesch
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Sep25-11, 12:21 PM
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Quote Quote by Vanadium 50 View Post
Second, the difference between a rotating earth frame and a stationary frame is essentially irrelevant. If you draw the space-time diagram for the setup, including
the GPS satellites (one is enough if you assume it's already synchronized) you will discover what they are measuring is very close to the interval between emission and detection, which is a Lorentz invariant.
Well, I don't want to know how the GPS system actually works, what counts is what is the result of it. If it gives you the synchronised reference time in a stationary frame, then you assume that they have build in all necessary corrections to do so.

What I wanted to say was that if you "synchronize" in a stationary reference frame Oxyzt, which means that at events "Emission" and "Reception" you measure "t" (the t of the reference frame Oxyzt), but you measure the distance between "Emission" and "Reception" in a frame Ox'y'z't' using worldlines of stationary points (that is, with 0 velocity in frame Ox'y'z't') so that it is easy to measure that distance in that frame, then you cannot combine this distance measured in Ox'y'z't' with a time measured on Oxyzt.

My question was what kind of time coordinate (in what kind of frame) is used in the GPS system (no matter how they actually do it, assuming they do it right), and I thought that it was only possible in an intertial frame. However, I stand corrected, this can also be a time on a rotating geode which also contains another "universal time" as I forgot about the GR correction.

But it DOES matter what reference frame one uses to define "synchronised time", because mixing a time coordinate from one frame and a distance from another is at the origin of all "paradoxes" in introductory SR, such as the pole-barn paradox and the like.

There are two corrections that need to be applied - one is the fact that LGNS is moving 50mph faster than CERN because of the earth's rotation: that's a 10-15 effect.
Which should then according to DH be annihilated by the geode effect.

The other is that the earth has moved between the emission and detection times by a few feet. That should be properly taken into account by the GPS receiver (and I have questioned this), and if it is, it's a 10-6 effect on the 10-5 effect, or 10-11.
That's if you're working in an inertial frame ! If you work in the rotating frame that is not the case. This is why defining the correct reference frame is so important, and rather tricky in this case.

The point is not that I think I'm smarter than those guys, it is just that nothing of all this was mentioned in the paper.
vanesch
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Sep25-11, 12:58 PM
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Quote Quote by PAllen View Post
How do you get the SR effect you claim? For gamma to differ from 1 by 1 part in 10^7, I get a required relative speed of 83 miles per second. For a relative speed of 1000 mph, gamma differs from 1 by 1 part in 10^12 or so.
I was talking about beta and thought about a series development in beta, but now you come to say it, for most relativistic corrections the first non-zero term term is beta-squared. So this pushes the effects indeed in the 10^-12 range or so.

I guess this closes the discussion about a relativistic effect due to earth's gravity or rotation...
dan_b
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Sep25-11, 01:31 PM
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Quote Quote by lalbatros View Post
Hello,

How was it possible to measure the time of flight with a 10ns precision, based on theis 10 Ás proton pulse?

Thanks for your help.

Michel

(before eventually re-starting a specific thread focusing on data analysis)
One pulse does not have good enough signal to noise ratio to get a time of flight precision of a few ns. The proton pulse actually doesn't have much current in terms of everyday lab measurements, although it's a huge current in terms of teravolt particles. So they made a model by using many emitter pulses, and comparing many receive pulses to it. Several people pointed out that there can be hidden assumptions when that is done. For example, one hidden assumption might be that the emitter pulse is invariant shape, except for band-limited Gaussian noise. If that's wrong, then the mathematical processing used to put together the 'average' of many pulses goes a little wrong and might make a bias which could be unaccounted for.

All my tentative "might' and "could' words are because, they're smart guys and maybe they already did it just right, but a paper with that level of total detail in it would be unreadable! There's deep exam questions here about experimental technique, just as should be. It's a lot of work for them to answer even a few of the most carefully considered issues of the critics. This will take time. There is no way around it, and they understand that.
Vanadium 50
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Sep25-11, 02:43 PM
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Quote Quote by f95toli View Post
I'd say it is very common. GPS is one of two systems used for time transfer in the UTC itself meaning this is done routinely. Granted, it is the less accurate system, but the reason they used in here is presumably because it is good enough.
That's the point - who is using something more complicated than something you buy at Fry's for this particular application? The bigger the market for this, the less likely something is odd in the firmware.
xeryx35
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Sep25-11, 03:05 PM
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Quote Quote by PAllen View Post
They said they used a 3-D coordinate system, which implies they considered this.
Sorry, didn't know that. But another problem arises with the use of GPS. The satellites which are making these measurements may slip a bit in their orbits - they are not in absolutely perfect geostationary orbits. Even a deviation of [itex]\pm[/itex]1 meter could have an enormous effect on the accuracy of the neutrino reading.
D H
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Sep25-11, 03:11 PM
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GPS satellites are not in geosynchronous orbits.

Whatever mistake was made, if a mistake was made, was quite subtle. That group has been building up this data for a few years. They looked for obvious explanations, not so obvious explanations, asked outside groups for help, and still couldn't find anything that explained their results.

I'm guessing that they did do something wrong. I'm also guessing that we at PhysicsForums will not be the ones to ferret that mistake out.
xeryx35
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Sep25-11, 03:13 PM
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Quote Quote by D H View Post
GPS satellites are not in geosynchronous orbits.
It does not matter, there may be +/- a few meters of orbital deviation.

Whatever mistake was made, if a mistake was made, was quite subtle. That group has been building up this data for a few years. They looked for obvious explanations, not so obvious explanations, asked outside groups for help, and still couldn't find anything that explained their results.

I'm guessing that they did do something wrong. I'm also guessing that we at PhysicsForums will not be the ones to ferret that mistake out.
True.
Lord Crc
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Sep25-11, 03:29 PM
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Quote Quote by PAllen View Post
They said they used a 3-D coordinate system, which implies they considered this.
As I mentioned earlier in this thread, they said in the presentation that they corrected for GR due to the height difference, and that the correction was on the order of 10^-13.
D H
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Sep25-11, 03:40 PM
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Quote Quote by xeryx35 View Post
It does not matter, there may be +/- a few meters of orbital deviation.
No. Try centimeters.

Furthermore, the errors in the orbit estimations are irrelevant here. Those experimenters used common view mode, which reduces errors in both relative time and relative position by orders of magnitude. Common view mode, relative GPS, and differential GPS have been around for quite some time. The basic concept is thirty years old, but not the 10 nanosecond accuracy claimed by the experimenters.
Lord Crc
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Sep25-11, 03:48 PM
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Quote Quote by D H View Post
The basic concept is thirty years old, but not the 10 nanosecond accuracy claimed by the experimenters.
In the presentation they said that this precision was common place, just not in the field of particle physics. Did I misunderstand?
xeryx35
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Sep25-11, 03:55 PM
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Quote Quote by D H View Post
No. Try centimeters.

Furthermore, the errors in the orbit estimations are irrelevant here. Those experimenters used common view mode, which reduces errors in both relative time and relative position by orders of magnitude. Common view mode, relative GPS, and differential GPS have been around for quite some time. The basic concept is thirty years old, but not the 10 nanosecond accuracy claimed by the experimenters.
The software could have been buggy, it may be like that for something which is not commonplace like that. There are a thousand other factors which could affect the results. No single factor was responsible for this.
dan_b
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Sep25-11, 04:30 PM
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Quote Quote by lalbatros View Post
Thanks dan_b.
I could not locate a paper describing the "likelihood function" with seems to be the basis for their analysis. Would you have some track for such a paper, or would you have some personal idea about it? ....

Michel
Hi Michel,

Likelihood function = probability density function. Just a different name maybe with different normalization. I apologize in advance because I don't think you're going to like this link very much. I don't. It has an approach which obscures the intuition if you not comfortable with the math. It also has links which may be useful. Keep following links, use Google search on the technical terms, and eventually you'll find something you're happy with. Try starting here:

http://en.wikipedia.org/wiki/Probabi...nsity_function


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