CERN team claims measurement of neutrino speed >c

[xts]

have neutrinos ever been observed at low speeds or rest? Or do we always see them travel at the speed of light, give or take small differences?

No. Neutrinos of so small energies could not be measured. All the observed neutrinos are highly relativistic. We could take them as massless - except we observe their oscillations, which prove they must have small, but non-zero mass.

How are they insuring that the neutrinos in Gran Sasso are the same neutrinos from CERN? There is no way to tag these objects. If there are billions of neutrinos passing through our eyes every second, is it possible that this could be neutrinos from another source?

Gran Sasso detector is tuned to detect high energy (~17GeV) neutrinos, incoming from precisely defined direction (pointing to CERN).
The background of neutrinos is mostly in thousand times lower energies (solar neutrinos), and the flux of high energy ones is pretty small, when compared to the beam coming from CERN.
Guys at OOPERA estimate the cosmic background events as about 0.5% of the events they used for the analysis.

 

[Haelfix]

How are they insuring that the neutrinos in Gran Sasso are the same neutrinos from CERN? There is no way to tag these objects. If there are billions of neutrinos passing through our eyes every second, is it possible that this could be neutrinos from another source?

This answer just seems too obvious, but how are they confirming that the neutrinos from CERN are the same as the ones at Gran Sasso.

The cross section of cosmic rays that you can measure is many times smaller than the flux of neutrinos prepared by the experiment. So this is just another example where you need to proceed statistically by taking many events in a short enough time frame..

More generally, it is true that this is not a direct experiment. There is no direct measurement of when and where the actual neutrinos are created, and so there is an uncertainty in the actual positions and timings of departure. Now, there is a statistical procedure that is utilized whereby those quantities can be recreated on average, and they seem to have done a pretty thorough job imo, but it is still a source of systematic uncertainty and the details are technical.

 

[slam7211]

Did they correct the distance between the 2 labs for SR effects?

 

[PeterDonis]

The neutrinos were reported to arrive 60 nsec earlier than expected. This corresponds to traveling 18 meters. Is it possible that the early arrival of the neutrinos was the result of them taking a more direct route than other particles through the dips and rises of curved spacetime? Perhaps they did not exceed the speed of light but, rather, took a shortcut.

I am unable to calculate the curvature of spacetime to obtain an estimate of the size of the curvature caused by the Earth's mass (apparently a hairy set of equations and way, way beyond me). Is there 18 meters that could be saved over the 700 km path?

I had the same thought, but no. See post #177.

 

[diggy]

Although the SN1978A results do challenge OPERA's, I don't think there are enough energy-data-points for the two results to rule one another out (i.e. who knows what's happening in between, these territories just aren't measured to the necessary precision yet).

It would be nice to see if MINOS could tighten up their measurement, which I'm sure they will be looking into since it is such a hot topic now.

If the results are "correct", I'm still a little baffled to understand why neutrino's would be special, compared to every other particle we've measured that seem to happily observe the speed of light as law. I will need to go review the FTL neutrino models out there.

Exciting times!

 

[Parlyne]

If Cherenkov radiation occurs when a particle travels at >c in a medium, does that mean that if you passed a neutrino through a vacuum the resultant blue glow (or lack thereof) would give you an answer as to whether the speed limit has been broken?

Please forgive my basic understanding of this, I am only in high school.

Cherenkov radiation is a strictly electromagnetic effect. Neutrinos have no electric charge; so, they can't radiate in that manner.

 

[harrylin]

Did they correct the distance between the 2 labs for SR effects?

Good question! I can imagine they did not (or wrongly!) account for it. Although people there routine use SR for their experiments, the frame transformation between the ECI frame and the lab frame is often glossed over, overlooked or misunderstood. Of course also the GR effect must be taken in account (which would affect to the opposite I guess; and according to post 177 it's negligible).

I vaguely recall that there has been a similar issue in astronomy in the past, with claims that the speed of light was in fact c+v, followed by silence on that issue and then no problem at all.

PS here's the link to their Arxiv paper (if someone already gave it, then here it is again):
http://arxiv.org/abs/1109.4897

 

[FlexGunship]

That's, what? 1.00002 c?

I understand the big deal with respect to general relativity. I'm not sure that it's a big deal from a practical point of view.

(1) Based on current understanding it means that the neutrino has negative mass. It could possibly account for the expansion of the universe if it's found that each neutrino has a very slightly repulsive effect on all matter in the universe.

(2) If it has positive mass and still travels faster than the speed of light, then it'll overturn... um... every equation with the number "c" in it, not the least of which will be E=mc².

(3) If it's a measurement error that has been confirmed to this degree, then it will tell us something about our current understanding of metrology and measurement sciences. Remember that this result was first reported by MINOS in 2007, this is a confirmation experiment.

Keep in mind that these folks compensated for CONTINENTAL FREAKIN' DRIFT! I hardly think they forgot time dilation and special relativity effects.

All that being said, I believe we will find that neutrinos travel below the speed of light, but that we will learn something new about our measurement techniques.

 

[seerongo]

This morning's Dario Autiero seminar video link was posted on post 187, but it was apparently not available at that time. Here it is again.

http://cdsweb.cern.ch/record/1384486"

It should answer a lot of questions asked here concerning methodology, etc,. in addition to the paper.

 

[PAllen]

Just want to record here a speculation on error source from Lubos Motl's blog that doesn't seem to have been raised here. I didn't notice any discussion of this in the arxiv paper.

The issue is simply that light travels slightly slower in air than in vaccuum. This would mean that estimates of distance inferred from signal travel times to or from the GPS sattelites would be small by a tiny amount, unless this is corrected for. Calculations of this effect suggest it could scale the 730 km by around the right amount.

I wonder about the plausibility of this: it would suggest that all GPS distances are slightly scaled down, and no one noticed. Presumably, this would have little impact on navigational uses, but I'm not sure ... what about high precision military uses?

 

[PAllen]

Just want to record here a speculation on error source from Lubos Motl's blog that doesn't seem to have been raised here. I didn't notice any discussion of this in the arxiv paper.

The issue is simply that light travels slightly slower in air than in vaccuum. This would mean that estimates of distance inferred from signal travel times to or from the GPS sattelites would be small by a tiny amount, unless this is corrected for. Calculations of this effect suggest it could scale the 730 km by around the right amount.

I wonder about the plausibility of this: it would suggest that all GPS distances are slightly scaled down, and no one noticed. Presumably, this would have little impact on navigational uses, but I'm not sure ... what about high precision military uses?

It looks like the discussion on Motl's blog used the refractive index of air for visible light. I would expect this does not apply to radio waves - it would be some other value. My guess (presumably others here would know better) the refractive index for radio is smaller, maybe small enough that it can be completely ignored even at the precision of these measurements.

[EDIT: I found at least one university source that claims air's refractive index for radio waves is similar to visible light. However, it further explained how this regularly must be accounted for in radio transmission applications, so it now seems preposterous that GPS doesn't account for this.]

 

[xts]

Speed of light in air (and in ionosphere - which is more important, as it varies much more) is taken into account and compensated even by simple car navigator GPS's. So it might not be an issue here. Professional GPS's compensate it on several methods, with accuracy of single cm.

Off-topic: we are now in solar activity maximum year, so the ionoshere is densier and thicker than usually. In some situations, when one of the satellites is just above the horizon, older car navigators (unable to receive WAAS corrections) may show your position displaced by 30 meters or so off the road - that happened to me few days ago.

 

[Enthalpy]

Read (too quickly) the paper from arXiv.

My first comment is that I'd strongly prefer the propagation time to be measured between two neutrino detectors, one at Cern and the other at Gran Sasso. Presently it's measured between a proton beam current detector at Cern and a neutrino detector at Gran Sasso. As the neutrino beam is 3km*3km wide at arrival, a small detector at the source would provide as many event there for a more direct comparison - err... IF the mu neutrinos can be detected with the same inefficiency as the tau neutrinos are, which I ignore to a high degree of precision.

GPS signals are jammed but many techniques, especially differential GPS, overcome it. From the comments in the paper, scientists there obviously know that better than I do and took care of these clock and position measurements, end of paragraph.

The signal from the proton beam intensity shows a decline instead of a steady plateau. Could it be that a fuzzy signal from the neutrino detector correlates better with the inclined reference if it's shifted forward, just as a result of the waveforms?

Now, things I'm easier with.

The 200MHz modulation of the proton beam brings no certainty at all to the discussed 30ns. If the slower beam current envelope, lasting 2µs, could be measured with 5ns certainty, then the 200MHz modulation would improve the correlation precision to about 10ps, which isn't the case here. The measurement relies only on the 2µs envelope.

I believe to understand that 200MHz is the frequency of the accelerator cavities, and modulate the beam intensity fully, something like 0% to 200% of the mean intensity. Though, the diagrams on page 6 show only +-15% modulation depth at 200MHz, so even though the beam current transformer and supposedly the acquisition device have a broader bandpass than 200MHz, something attenuates the 200MHz component, be it a medium to long cable or something else.

Unfortunately, the thing that attenuates at 200MHz is probably dispersive, that is, it introduces a propagation delay that depends on the frequency. A cable for instance delays precisely at 200MHz by its known speed but gets slower at lower frequency as its series resistance adds to the inductance, and here we're talking about 30ns precision over a 2µs waveform with 500ns transitions - that is, the measurement results from a rather strong statistical interpolation.

Hence I wish this possible dispersion be eliminated. Fortunately, this looks easy, thanks to the 200MHz modulation. It just needs to suppress the DC and LF components of the signals, both at Cern and at Gran Sasso, and compare only the tone-burst envelope. It needs a filter around 200MHz, a broad one like 100-300MHz to minimize its propagation time. Over this favourable and limited frequency band, all cables and transformers will show their normal delay. Maybe these filters can be made by the same piece of software, introducing the same delay. The correlation will oscillate at 5ns, but this is meaningless. The envelope of the correlation will be meaningful and independent of LF dispersion.

Marc Schaefer, aka Enthalpy

 

[KWillets]

http://lmgtfy.com/?q=gps+atmospheric+correction

But I suppose it's worth saying there's also a lot of cross-calibration, measurement from known points, etc., so it would be hard for an error to creep in.

 

[PeterDonis]

Good question! I can imagine they did not (or wrongly!) account for it. Although people there routine use SR for their experiments, the frame transformation between the ECI frame and the lab frame is often glossed over, overlooked or misunderstood.

By my calculations, this potential source of error is even smaller than the GR correction. Just for an order of magnitude estimate, the velocity of an object at rest on the Earth's equator, relative to the ECI frame, is about 450 m/s, or about 1.5 x 10^-6 c. That gives an SR correction due to the relativistic gamma factor on the order of 10^-12, which is two orders of magnitude smaller than the GR correction Vanadium 50 gave in post #177.

 

[harrylin]

By my calculations, this potential source of error is even smaller than the GR correction. Just for an order of magnitude estimate, the velocity of an object at rest on the Earth's equator, relative to the ECI frame, is about 450 m/s, or about 1.5 x 10^-6 c. That gives an SR correction due to the relativistic gamma factor on the order of 10^-12, which is two orders of magnitude smaller than the GR correction Vanadium 50 gave in post #177.

I did not consider gamma but the first order effect (Sagnac effect) which is not clearly mentioned in the paper. Anyway, I just followed up on it and made a calculation and compared it with the paper: I found that the effect of the speed of the surface of the Earth at that location (at most several 100 m/s) is at least one order of magnitude less than the cause that we are after. Indeed the >7 km/s that they found is really huge, one order of magnitude more than the speed of the equator!

Note that I still think that a GR correction should work the other way: light should be slightly slower at lower potential, right?

 

[PeterDonis]

I did not consider gamma but the first order effect (Sagnac effect) which is not clearly mentioned in the paper. Anyway, I just followed up on it and made a calculation and compared it with the paper: I found that the effect of the speed of the surface of the Earth at that location (at most several 100 m/s) is at least one order of magnitude less than the cause that we are after. Indeed the >7 km/s that they found is really huge, one order of magnitude more than the speed of the equator!

You're right, the Sagnac effect would be larger; I hadn't considered that because DaleSpam posted about it already a while back in this thread.

Note that I still think that a GR correction should work the other way: light should be slightly slower at lower potential, right?

I wasn't thinking about the time but the distance; whether GR corrections to the metric could significantly affect the computation of the distance traveled (and therefore the computation of the light travel time) from the GPS positions of the endpoints. (And as post #177 makes clear, this potential correction is much too small to matter.)

 

[JamesEitz]

With the data available. I have calculated the speed of the Nu = 299792465.4
m/s

 

[jbar18]

(1) Based on current understanding it means that the neutrino has negative mass. It could possibly account for the expansion of the universe if it's found that each neutrino has a very slightly repulsive effect on all matter in the universe.

This doesn't make much sense to me. I'm no expert, but if c is the real universal speed limit, surely anything traveling faster than c would still be measured to any observer to be traveling slower than c (symmetrically around c maybe?). I am very possibly wrong here.

Based on my own intuition, I would imagine that the measurement is probably some systematic error, but if not I would put my money on c being slightly faster than the speed of light. Since that would apparently change GR, which has held up pretty well so far, I would guess that it is almost certainly some systematic error.

 

[jobyts]

This morning's Dario Autiero seminar video link was posted on post 187, but it was apparently not available at that time. Here it is again.

http://cdsweb.cern.ch/record/1384486"

It should answer a lot of questions asked here concerning methodology, etc,. in addition to the paper.

As per the second slide in the presentation, the OPERA collaboration includes 160 physicists from 30 institutions. Does that mean, the 160 scientists are unable to find a fault with the procedure yet? If so,it is highly likely that there is no issue with the experiment.

 

[unusualname]

neutrinos do not have negative mass, there is no retrocausality and Einstein's SR is not proved wrong - I hope :-D

Most of the believable explanations have been put forward, but let us not assume that the experimental team are incompetent - perhaps they have in fact found that neutrinos are closer to the invariant speed required by SR than photons.

So why the wrong delay from light-year distant objects? Well, perhaps neutrinos interact with matter in a much more weaker way than photons (probabilistically weak) so that the delay effect is not noticeable over a few hundred kilometers but is noticeable over light-years.

photons travel VERY close to the invariant speed, but neutrinos travel EVEN CLOSER to the invariant speed (neither travel EXACTLY AT the invariant speed)

 

[harrylin]

As per the second slide in the presentation, the OPERA collaboration includes 160 physicists from 30 institutions. Does that mean, the 160 scientists are unable to find a fault with the procedure yet? If so,it is highly likely that there is no issue with the experiment.

I would agree if they accounted for the biggest possible causes that people here came up with. However if, like me, you cannot find where for example they accounted for the Sagnac effect (which is not obviously negligible), then there is good reason to suspect that they could very well also have overlooked something even bigger.

 

[xts]

160 physicists from 30 institutions. Does that mean, the 160 scientists are unable to find a fault with the procedure yet?

Of those 160, 140 are on the list, but did not work on the article and got even more surprised by it than we are. And remaining 20 - well - they are already biased by 5 years spent on the experiment.

There are even bigger ensembles of people, unable to internally discover their faults. To avoid drastic examples - think about 500 pers engineering team of [car-manufacturer-not-to advertise-it] who were unable to find that the brakes they designed are likely to block, or engineering team of aircraft manufacturer, who learned or air crash they made school-like error designing some detail of the construction.

Such experiment is a big, awfully complicated engineering task, where any of a million of details may cause a fault.

 

[ghwellsjr]

As I read it, the clocks are synchronized using GPS. Just having them identical doesn't account for time dilation if they are at different altitudes (i.e., different levels of gravitational potential), which I believe they are. There has to be some mechanism for correcting their rates to a common standard of simultaneity. That's what the GPS part is for (and it looks like it requires pretty hefty GPS equipment to get that kind of accuracy for the corrections).

Also, I see very precise measurements of distance, but they are all based on GPS location fixes, as far as I can tell. I see a reference to a "common analysis in the ETRF2000 reference frame", but there are no details, just a pointer to a reference at the end of the paper that isn't online. So I can't see if the reference frame they used for their computation of the distance, based on all the measurements, took into account that distance, as well as time, gets distorted when the altitude (i.e., gravitational potential) changes. I would think it would, since they talk about a geodetic survey, which is all about accurate measurements of equipotential surfaces. But it would be nice to have more details.

Isn't it the case that clocks at different altitudes will tick at different rates which means they can never be synchronized, so how can there be a single value for the time difference between these two locations? So how can they precisely define the one-way speed of light between these two locations?

 

[PAllen]

A lot of the measurement builds on the accumulated technology behind the GPS, which the paper authors assume without going into detail. For example, the sagnac effect is fully accounted for within the GPS measurements themselves:

http://relativity.livingreviews.org/Articles/lrr-2003-1/

 

[aleazk]

I was thinking along the same lines as jbar18. The most obvious explanation is that light travels slower than c. Photon mass won't do it (as per my previous post) but some other mechanism might.

So I was wondering if we have any very accurate measurement of c which is independent of measuring the the speed of light. Can we for example measure the deflection of light by the sun accurately enough to determine c to better than one part in 50,000? I don't know but I would be surprised. The best test might be in particle accelerators. The decay times of highly relativistic particles depend on actual c, not the speed of light. Does anyone know what limits that puts on c?

I totally agree, I think the limit velocity is real but I never asked myself at what extent we know that the numerical value of c is that of the speed of light. For this reason, I think the best way to attack the causality proposition experimentally it is by measuring the consecuences, like the particle-antiparticle mass equality, or the existence of black holes.
Maybe in the future we could measure the velocity of gravity waves, which is the actual c. I think we don't have yet a sufficiently precise value of the deflection of light by the Sun to calculate the actual c.

 

[Vanadium 50]

How are they insuring that the neutrinos in Gran Sasso are the same neutrinos from CERN?

You turn the accelerator on, and you see neutrinos in Opera. You turn it off, and they stop. Looks pretty convincing to me. Figure 11 in the paper shows that on a very short time scale.

 

[seerongo]

As per the second slide in the presentation, the OPERA collaboration includes 160 physicists from 30 institutions. Does that mean, the 160 scientists are unable to find a fault with the procedure yet? If so,it is highly likely that there is no issue with the experiment.

Curtain #1: Neutrinos are faster than c.
Curtain #2.: A group of very careful, smart human beings have not yet found a subtle problem in a very complex system (or study design).

While the jury is still out, if I were a betting man, I think I'd bet on curtain #2. Either curtain is sure to have something interesting, though

 

[PAllen]

Isn't it the case that clocks at different altitudes will tick at different rates which means they can never be synchronized, so how can there be a single value for the time difference between these two locations? So how can they precisely define the one-way speed of light between these two locations?

The clock rates are all adjusted via signals (all part of GPS). Effectively, the local clocks are adjusted not to measure local time but synchronized time. They don't measure one way speed of light - they assume it, and the distance is actually a measure time * c (indirectly, using triangulation, all based on radio signals). If neutrinos traveled at exactly c, then (assuming no errors), by construction, they would measure the same 'time' between source and detector as the radio signals imply.

I think there must be a mistake somewhere, but it is clear to me they have not simply forgotten any of the following:

- gravitational time dilation
- sagnac effect
- speed time dilation
- atmospheric effects

 

[Pengwuino]

http://cdsweb.cern.ch/record/1384486

The webcast recording of the seminar involving the results is online.

 

[dgwsoft]

I totally agree, I think the limit velocity is real but I never asked myself at what extent we know that the numerical value of c is that of the speed of light. For this reason, I think the best way to attack the causality proposition experimentally it is by measuring the consecuences, like the particle-antiparticle mass equality, or the existence of black holes.
Maybe in the future we could measure the velocity of gravity waves, which is the actual c. I think we don't have yet a sufficiently precise value of the deflection of light by the Sun to calculate the actual c.

In fact we only know G to one part in 10^4 so using the deflection of light by the sun to accurately measure c is a non-starter. But I am sure there must be measurements at CERN that put a value on c entirely independent of the speed of electromagnetic waves. I would be very interested to know the error bars on that.

And to change tack - I hope this is not overly speculative - I rather like the idea that neutrinos are tachyons (which has been seriously proposed, as other posts here have pointed out). Also, this article may be relevant:

http://en.wikipedia.org/wiki/Lorentz-violating_neutrino_oscillations

any thoughts?

 

[ghwellsjr]

Isn't it the case that clocks at different altitudes will tick at different rates which means they can never be synchronized, so how can there be a single value for the time difference between these two locations? So how can they precisely define the one-way speed of light between these two locations?

The clock rates are all adjusted via signals (all part of GPS). Effectively, the local clocks are adjusted not to measure local time but synchronized time. They don't measure one way speed of light - they assume it, and the distance is actually a measure time * c (indirectly, using triangulation, all based on radio signals). If neutrinos traveled at exactly c, then (assuming no errors), by construction, they would measure the same 'time' between source and detector as the radio signals imply.

I think there must be a mistake somewhere, but it is clear to me they have not simply forgotten any of the following:

- gravitational time dilation
- sagnac effect
- speed time dilation
- atmospheric effects

I know they cannot measure the one way speed of light, that's why I asked how they can define it since the clocks at both ends will be running at different speeds. To boil the problem down, they look at what time it is on the local clock when the neutrinos are emitted and then they look at what time it is on the other local clock when the neutrinos are detected and the difference in time is how long it took the neutrinos to make the trip, but if time is running at a different pace at each location (and presumably all along the trip) then how can they make any sense of the times on the two clocks running at different rates?

I don't see how clocks adjusted by GPS can get around the concern that I have. Consider the atomic clocks at Greenwich and Boulder running at different elevations and therefore running at different rates. If we measured the round-trip speed of light at both locations using their own atomic clocks, we'd get the correct answer of c. But if we used a common time generated by GPS, we will no longer get the correct answer of c at both locations, correct?

 

[PAllen]

I know they cannot measure the one way speed of light, that's why I asked how they can define it since the clocks at both ends will be running at different speeds. To boil the problem down, they look at what time it is on the local clock when the neutrinos are emitted and then they look at what time it is on the other local clock when the neutrinos are detected and the difference in time is how long it took the neutrinos to make the trip, but if time is running at a different pace at each location (and presumably all along the trip) then how can they make any sense of the times on the two clocks running at different rates?

But they adjust each clock to not run at local time, but instead run at the time rate and value of the GPS synthetic frame. Constant re-synchronization is done to achieve this. This is the core of how GPS works - all clocks involved are adjusted for time dilation of all flavors; atmosphere signal delays; sagnac effect; etc. read the paper I linked a few posts back.

I don't see how clocks adjusted by GPS can get around the concern that I have. Consider the atomic clocks at Greenwich and Boulder running at different elevations and therefore running at different rates. If we measured the round-trip speed of light at both locations using their own atomic clocks, we'd get the correct answer of c. But if we used a common time generated by GPS, we will no longer get the correct answer of c at both locations, correct?

Yes, that's true, but not relevant to what they are doing.

 

[DevilsAvocado]

Well, if this doesn't invalidate Special Relativity (which pretty much does), the neutrino speed surprasses so slowly the speed of light that in order for you to send a message to the previous day, it would take longer than your lifetime.

True, they have chosen not to interpret in terms of new physics, which is wise at this stage. However if the results survive further testing... and FlexGunship’s (2) is the answer, we have a problem with causality, no matter how small... IMHO

There is no way to be "a little pregnant" (according to current knowledge).

 

[SeventhSigma]

Wait why did the neutrinos of that supernova arrive 3 hours earlier if we're going to assume this experiment is wrong and c is still the ultimate speed limit? How can neutrinos beat light if they have mass?