CERN team claims measurement of neutrino speed >c

[Dale]

So then c would be the "speed limit", and the speed of light would be something slightly less...

Exactly.

This still doesn't explain why photons have the same speed no matter your reference point.

It would be explained due to the fact that our measurements were not sufficiently sensitive until now. Of course, that is quite a statement and I think would require an extensive review. But that is the only way that this result could be confirmed and be compatible with previous data.

 

[Dale]

Maybe were saying the same thing here.

I'm not trying to say the math will be invalid. Is that what you're trying to say here?

I'm trying to say the predictions of the theory will be different, if C is not an invariant.

take:

ds^2 = -c^2*dt^2 + dx^2

Think about the physical interpretations and predictions of this equation with c constant, as we currently think about it.

Now, take c as something that is no longer invariant between inertial frames. Do we have the same outcomes from this equation, or from our theory in general. I don't think so.

How would natural units even work, which would make c=1 in the equation above, if it was variable, which it would have to be if photons have mass?

No, we are not saying the same thing. The constant c must be invariant for SR to hold, but light need not travel at c and SR would still hold.

 

[jtbell]

anything out there that is not a news story but a real paper?

Rumors and speculations travel faster than light. Real data and publications are a bit slower.

 

[Haelfix]

Theoretically, SR and GR can be made compatible with having a nonzero photon mass. You give up gauge invariance, and introduce a lot of finetuning in nature, but then it is not explicitly ruled out (albeit experimental limits on the Proca mass are genuinely tiny).

However SR is not compatible with having massive tachyonic fermions. It would lead to violations of causality.

Somewhat more interestingly, SR is compatible with massless scalar tachyons, but you don't interpret them in the same way (it leads to the spontaneous decay of our vacuum) and you can almost always reinterpret them in a way that preserves the causal structure of spacetime.

 

[Borek]

Edit: I should also add, my first thought upon reading the BBC news article was to wonder how on Earth they measured the distance of about 730 km to the required accuracy...

GPS can be used to measure distance with very high accuracy (up to centimeters if memory serves me well). This is routinely used to measure displacements of ground in seismically active places. This type of measurement is very slow (unless you have a military device that can decrypt coded part of the signal), but that doesn't matter here - they had plenty of time. And as 1 feet is a 1 ns errors in distance measurements should be not a problem.

 

[ZapperZ]

That would not work for a lot of reasons, the main one of which is that the neutrinos tunnel right though the Earth in a straight line from Cern to the detector in Italy. There is no equivalent path for light, so the separation of the emitter and detector needs to known somehow. I'll have to dig into Opera faqs, etc to see how the distance was known well enough to measure such a small variation from c.

This is incorrect. The neutrinos DO NOT TUNNEL through the earth. They interact only via weak interactions (and very, very weakly with gravity). "Tunneling" is a different physics entirely!

Zz.

 

[turbo]

This is incorrect. The neutrinos DO NOT TUNNEL through the earth. They interact only via weak interactions (and very, very weakly with gravity). "Tunneling" is a different physics entirely!

Zz.

Noted. Please chalk this up as a poor choice of words. Neutrinos interact so weakly with matter that they can zip through (not tunnel through) impressive amounts of matter without leaving a trace of interaction. Thus, you need a big sensitive detector, and LOTS of neutrinos to get statistically-significant detection-signal. Apparently, Opera was designed with this in mind, and successfully so. Are the results reliable, and are they repeatable with other instrumentation? Time will tell.

 

[PeterDonis]

I'll be interested to see exactly how they calculated what the light travel time should have been. Did they properly account for the fact that the direct path goes through the Earth's interior, and therefore the actual path length will be different than the path length that would be inferred if you just took the differential, in Euclidean geometry, between the two GPS locations, because of GR effects (the difference in spacetime curvature)? My initial guess is that the corrected "through the Earth" path length will be slightly *shorter* than the uncorrected path length you would infer from the differential in GPS locations, which would explain the results. But I haven't done a calculation to see for sure.

 

[atyy]

Newly posted by MTd2 on marcus's quantum gravity bibliography:

http://arxiv.org/abs/1109.4897
Measurement of the neutrino velocity with the OPERA detector in the CNGS beam
OPERA
(Submitted on 22 Sep 2011)
The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos. The measurement is based on high-statistics data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (60.7 \pm 6.9 (stat.) \pm 7.4 (sys.)) ns was measured. This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c = (2.48 \pm 0.28 (stat.) \pm 0.30 (sys.)) \times 10-5.

 

[DrGreg]

http://arxiv.org/abs/1109.4897
Measurement of the neutrino velocity with the OPERA detector in the CNGS beam

Note the final paragraph:

Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.​

 

[Jack21222]

I'm kinda hoping that there is some sort of compact extra dimension explanation to come out of this (because my research advisor would do a literal jump for joy), but I recognize that this is far far FAR more likely to be just some experimental error.

 

[Runner 1]

Well one thing is for certain:

When the paper is released, we'll see a bunch of internet physics experts discover the obvious flaw that multitudes of particle physicists just happened to overlook during 3 years ;)

 

[seerongo]

Whether this is an error in methodology/measurement or it is verified that neutrinos are faster than photons and photons are slower than c and massive, etc., the outcome should be very interesting in any case. This group is not stupid and have had 4 years to figure this out. It seems to me that any outcome is bound to have important implications, even an experimental anomaly, since so many experiments are based on similar methodologies. Anyone here care to speculate on that end of it (since speculation is all we have today)? Comments here so far seem too focus on errors in measuring source/detector separation, equipment latencies, etc, but certainly they have gone over that ground ad nauseum.

For purposes of this discussion if nothing else, can we agree to differentiate the terms "speed of light" and "c", with "c" being the zero-mass SR speed limit? Using them interchangeably can be confusing in a discussion like this.

 

[Dale]

I don't understand why everyone in this thread seems to be assuming that a massive photon will explain this. The value of c is used in so many formulas used by physics. If we'd been using the wrong formulas since the early 1900s, wouldn't somebody have noticed their inaccuracy?

Newton's laws were used for about twice as long before anyone noticed any inaccuracies.

 

[Vanadium 50]

This is a systematic effect. You can take that to the bank.

They don't see a velocity dispersion. By itself, that's a huge problem. If you want to argue that not only are neutrinos faster than light, but they all travel at the same speed regardless of energy, you have to explain why the neutrinos from SN1987A arrived on the same day as the light did, instead of (as the Opera data would indicate) four years earlier.

 

[Vanadium 50]

A massive photon won't explain this. All photons travel at the same speed. If the limiting speed were 1.000025c, we would see more energetic photons move faster, and we don't.

 

[Dale]

A massive photon won't explain this. All photons travel at the same speed. If the limiting speed were 1.000025c, we would see more energetic photons move faster, and we don't.

Yeah, I have to agree here. I just looked at the paper, the effect is too large to have hidden in the noise for all previous experiments.

 

[Jack21222]

+1

I think there is an inverse relationship between the speed at which one dismisses other's works and the number of their own great works.

One can both dismiss and investigate a claim at the same time. I'd be very interested in seeing where the error is. For what it's worth, the CERN team is "dismissing" their own results here. It's still fun trying to pinpoint what could have went wrong.

The point about the SN1987A neutrinos is a big one. I just did the calculations myself... the neutrinos would have arrived 4 years earlier than they did, as V50 says.

 

[PeterDonis]

Differences in time dilation due to a slightly different gravitation field? Bzzzt, wrong, two identical Cs clocks, one at each location with a measured error of 2.3 ± 0.9 ns.

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.

 

[PeterDonis]

The point about the SN1987A neutrinos is a big one. I just did the calculations myself... the neutrinos would have arrived 4 years earlier than they did, as V50 says.

The paper mentions SN1987A, and notes that the energies of those neutrinos were several orders of magnitude smaller than those of the CERN neutrinos in this experiment. So one could try to account for the SN1987A results and these consistently by postulating a really wacky dispersion relation for neutrinos, that caused virtually no dispersion at energies around the SN1987A energies, but yet caused significant dispersion at the CERN neutrino energies. I don't know if any reasonable physical models for neutrinos would imply such a dispersion relation.

 

[Dale]

They did not measure the speed of photons moving between the same points at the same time. They measured neutrinos to go faster than *c*.

Correct, they are claiming the the neutrinos travel at 299 799 893 m/s compared to the speed of light 299 792 458 m/s. So the massive-photon resolution would require that the invariant speed be something greater than 299 799 893 m/s, but that would have been detectable in other experiments.

 

[Haelfix]

Correct, they are claiming the the neutrinos travel at 299 799 893 m/s compared to the speed of light 299 792 458 m/s. So the massive-photon resolution would require that the invariant speed be something greater than 299 799 893 m/s, but that would have been detectable in other experiments.

The bottomline is there is no way this can work theoretically. You could for instance look for departures from Lorentz invariance, but that's already been searched for ad naeusum through several different channels. No known violation of the SR dispersion relations have ever been discovered, and the bounds are already far in excess of the sensitivity of this experiment.

It also contradicts well established neutrino measurements, like the Supernova ones. Trying to stay consistent with that, leads you into real absurdities (like modifying standard MSW physics in violent ways)

 

[seerongo]

Correct, they are claiming the the neutrinos travel at 299 799 893 m/s compared to the speed of light 299 792 458 m/s. So the massive-photon resolution would require that the invariant speed be something greater than 299 799 893 m/s, but that would have been detectable in other experiments.

Thanks for clarifying that.

So now that the paper clears that up, it appears the photon can resume it's original svelte, speedy status as "c". This sure is starting to look like an error in position measurement. Not as much fun, but still would be important, since they must have been closely studying that possibility all along.

I suppose the little ones could be taking an extra-dimensional short cut or a convenient worm hole, but they'd all have to be taking the same short cut every time for years. I dunno...

Thanks to those who are summarizing the paper's details for us non-physicists.

 

[qsa]

http://indico.cern.ch/conferenceDisplay.py?confId=155620

 

[Chronos]

Agreed, the OPERA team is seeking confirmation [I agree with Pallen it appears unlikely]. Neutrino detection is tricky business and correlating capture with emission is no easy task. I can't help but wonder how many of the detected neutrinos were actually emitted by CERN and how that might skew the measurement. There was a paper about 10 years ago about neutrinos as tachyons by Chodos, IIRC.

 

[seerongo]

Agreed, the OPERA team is seeking confirmation [I agree with Pallen it appears unlikely]. Neutrino detection is tricky business and correlating capture with emission is no easy task. I can't help but wonder how many of the detected neutrinos were actually emitted by CERN and how that might skew the measurement. There was a paper about 10 years ago about neutrinos as tachyons by Chodos, IIRC.

My background is engineering, not physics, but frankly, the method used to correlate the proton extractions with the v detections doesn't seem that bad to me so far, although at first blush, 16,111 detected events doesn't seem too great statistically. I'd like to see more expert comments on that however. Regarding potential contamination, would most contamination come from B-decay, which would be anti's? I think they accounted for anti's, counting about 2% unless I read it wrong. Could someone comment on that? I'm not sure about the potential sources of spurious neutrinos in significant numbers.

I'm more struck by the timing aspects. There seem to be so many places in this system where inaccuracies can gang up on you. This is a pretty complex system with a lot of timing points, all with tolerances. I'd be the last person to second guess this work, but I think that's where I'd look.

 

[Gilles]

I think the question of clock synchronization may be tricky. In GR, there is no absolute definition of simultaneity. Due to differences in gravitational potential, as mentioned, clocks evolves differently at different points. So you must periodically resynchronize them, but how ? there is no unique choice, and the measured time of flight probably depends of how you define the timescale at each point.

 

[Parlyne]

There is one remote possibility I have not seen discussed in this thread.

Is it possible in theory that a neutrino has zero mass and the test is showing tachyonic properties? This would not violate SR.

An unlikely explanation but just wanted to see what an expert has to say.

I'm afraid that's already ruled as a reasonable explanation for this by supernova 1987A. The problem is that the speed of a tachyon is given by

v = c\sqrt{1+\frac{|m^2|c^4}{E^2}}.

This means that a tachyon's speed increases as its energy decreases. As noted above, the OPERA neutrinos have higher energy than the 1987A neutrinos, meaning that, were they tachyonic, they should be slower, not faster, than the supernova neutrinos. But, in fact, the 1987A neutrinos have a discrepancy from c that is, at worst, something like 4 orders of magnitude smaller than the OPERA discrepancy.

 

[JordanL]

I'm sorry, but I don't quite buy a slight tweak to our definition of "c" as a complete answer.

Anyone suggesting that simply adjusting the "c" constant will fix things needs to explain how 150 years of mathematical and physics equations didn't detect the discrepancy.

Looking to an adjustment to c as the answer to this data, if correct, is... creative. It is not borne out of a dedication to science but a fear of change, as given data like this, that is certainly not the most likely cause, even within our CURRENT theories.

 

[Dmitry67]

What if neutrinos are very high energy tachions, so we never noticed that they are moving slightly faster than c? We can't detect low energy neutrinos, so usually don't see them moving much faster than c.