CERN team claims measurement of neutrino speed >c

[turbo]

Edit:

Before posting in this thread, we'd like to ask readers to read three things:

1. The https://www.physicsforums.com/showthread.php?t=414380". Don't forget the section on overly speculative posts.
2. The paper http://arxiv.org/abs/1109.4897"
3. The previous posts in this thread

And original post:

Antonio Ereditato, who works at the CERN particle physics center on the Franco-Swiss border, told Reuters that measurements over three years showed the neutrinos moving 60 nanoseconds quicker than light over a distance of 730 km between Geneva and Gran Sasso, Italy.

I'll try to dig up a more detailed report, but if this result is confirmed elsewhere, would such a development be a wrinkle for SR, or something more important?

http://news.yahoo.com/particles-recorded-moving-faster-light-cern-164441657.html

 

[PAllen]

I'll try to dig up a more detailed report, but if this result is confirmed elsewhere, would such a development be a wrinkle for SR, or something more important?

There would be a race to determine the mass of the photon. It would be a huge surprise, but I think it would be a bigger hit for QED than SR or GR - the latter rely only on the fact that there is a spacetime structure speed limit. Whether a particular particle reaches it is irrelevant.

I would definitely take the bet against this being confirmed.

 

[Passionflower]

There would be a race to determine the mass of the photon.

I do not believe it would be that simple.

If we were to claim photons have mass then we would have to explain why photons are always observed to be going at c.

 

[turbo]

Touching on the subject of neutrino speed, synchronization, measurement difficulties, etc.

http://profmattstrassler.com/2011/09/20/supernovas-and-neutrinos/

 

[PAllen]

I do not believe it would be that simple.

If we were to claim photons have mass then we would have to explain why photons are always observed to be going at c.

As a practical matter, neutrinos 'always go at c almost c'. So if photons were slightly more massive than neutrinos, the same would be true.

 

[Passionflower]

As a practical matter, neutrinos 'always go at c almost c'. So if photons were slightly more massive than neutrinos, the same would be true.

You are missing the point, if photons have mass one needs to explain why unlike other particles with mass they are always measured at c regardless whether the measuring apparatus approaches or retreats from them.

 

[PAllen]

You are missing the point, if photons have mass one needs to explain why unlike other particles with mass they are always measured at c regardless whether the measuring apparatus approaches or retreats from them.

The same appears true of neutrinos at the level precision of measurement available, despite the general assumption that neutrinos have mass. The same could be true of photons.

I haven't missed any point.

 

[dm4b]

The same appears true of neutrinos at the level precision of measurement available, despite the general assumption that neutrinos have mass. The same could be true of photons.

I haven't missed any point.

The OP can correct me if I am wrong, but I don't think they were talking just about experiment. I think they were also talking about theory.

 

[PAllen]

The OP can correct me if I am wrong, but I don't think they were talking just about experiment. I think they were also talking about theory.

We're talking about possible interpretations of a possible experimental result. I am expressing the view that the first thing to consider is that photons have a tiny mass, similar to neutrinos. On this assumption, there are possibly no experiments counterfactual to the assumption, and SR/GR are not affected.

Of course this isn't the only possible interpretation. All this is premature anyway, since I really doubt this will be confirmed.

 

[muppet]

It's conceivable to me that light could travel at less than "the speed of light"; could, for example, effects such as the scattering of light by light slow down the actual propagation of photons through the vacuum?

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...

 

[millitiz]

I think I would need to read the methodology - how did they know that it is faster than speed of light? Because as muppet said, 60 nanoseconds is a difference of the order of 10 meters - and that could simply be error of measuring the distance. Then I thought maybe they somehow collect light originated from CERN - but that would be a bit amazing for the technique - because the intensity of the light would probably be on the order of background noise after traveling 700 km.

 

[turbo]

I think I would need to read the methodology - how did they know that it is faster than speed of light? Because as muppet said, 60 nanoseconds is a difference of the order of 10 meters - and that could simply be error of measuring the distance. Then I thought maybe they somehow collect light originated from CERN - but that would be a bit amazing for the technique - because the intensity of the light would probably be on the order of background noise after traveling 700 km.

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.

 

[millitiz]

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.

That is my point - if they somehow synchronize the neutrino with gamma ray from the emitter, then as I said, it would be an amazing technique because the light would be so scattered that it would be nearly none existing - and if they calculate the speed through distance/duration, then as I said, 60 nanoseconds is on the order of 10 m of differences. And from my limited knowledge, it could be an error somewhere. Although in the news (maybe not this one), they did check the result - and it also said that it is beyond statistic significance (I would assume it is 3 sigma? Although the news did not say anything about it) - then they probably did take into account of the error of measuring things.

I guess my bottom line is that, we will have to wait a bit longer, and as you noted, probably would have to dig around. I remember in the BBC news, it said that the team is going to talk about it soon. Although I would imagine it to be a false alarm...maybe.

 

[Jimmy Snyder]

Here is the msnbc story:
http://www.msnbc.msn.com/id/44629271/ns/technology_and_science-science/"
It seems that the measurement team is asking for confirmation, so don't be too hasty.

 

[kfmfe04]

There's an interesting article here regarding errors in GPS which could explain the discrepancy:

http://www.wired.com/wiredscience/2011/09/neutrinos-faster-than-light/

 

[Runner 1]

I'm curious -- some of your posts seem to be implying that you hope the experiment is not valid. Is this correct? Or are you just doubting that it is valid?

It seems to me like you would simply hope for consistency and wait for it to either be validated or refuted by multiple other groups.

 

[PAllen]

I'm curious -- some of your posts seem to be implying that you hope the experiment is not valid. Is this correct? Or are you just doubting that it is valid?

It seems to me like you would simply hope for consistency and wait for it to either be validated or refuted by multiple other groups.

Hoping for invalidity would not be a scientific sentiment. Interpreting a preliminary result in light of 'similar' preliminary results over the centuries is perfectly scientific. 'Almost all' experiments that contradict understanding derived from thousands of others turn out to errors; the few that don't are major milestones. So we really want to investigate this, but there is nothing wrong with observing that it is most likely a fluke. Note that a while back, the Tevatron announced a possible unanticipated particle; one of the authors of the paper wrote beautiful, long blog explanations about:

1) He was a paper author and all authors had done their best to account for experimental error.

2) His best guess remained (based on a career in particle physics) that this result was an irreproducible anomaly.

 

[nealst]

I'm curious -- some of your posts seem to be implying that you hope the experiment is not valid. Is this correct? Or are you just doubting that it is valid?

It seems to me like you would simply hope for consistency and wait for it to either be validated or refuted by multiple other groups.

The point at the moment is that nobody can tell from the news articles out there. There is only some pretty basic talk about the margin of error in the measurements but nothing more. On top of that the last months haven't been kind to "new stuff" (in the high energy physics world) that was hyped in the media. We're just cautious I guess.

 

[kfmfe04]

I'm curious -- some of your posts seem to be implying that you hope the experiment is not valid. Is this correct? Or are you just doubting that it is valid?

It seems to me like you would simply hope for consistency and wait for it to either be validated or refuted by multiple other groups.

Hope has nothing to do with it...

Instead, the nature of experiments suggests the possibility of being wrong somewhere in measurement of error is much higher than an experimental result disproving a well-established theory (however exciting that possibility may be!).

At this level of experimentation, you are dealing with extreme precision in time and distance measurements - at a 60 nanosecond differential, even latency in electronics/computers processing could potentially muck up your results.

 

[JordanL]

It should be noted: they performed the experiment 15,000 times before reporting results, and the calculation error on their measurement is said to be +/- 10ns, or one-sixth the differential.

I'm not sure what to think until the experiment is repeated elsewhere, but it seems CERN didn't make this statement lightly. They've been seeing this result since experiments in 2007.

 

[James Leighe]

I learned about this then came here... I guess there are no formal papers?

Maybe light does have a mass after all! You kinda have to pretend it does anyway as an intermediate step in qft calculations so I would not be terribly surprised... But this is still pretty shaking stuff.

Gonna be in the back of my mind all weekend... Someone needs to confirm!

 

[atyy]

Death to SR!

A review of current photon mass limits is http://arxiv.org/abs/0809.1003

Lorentz invariance limits are in http://arxiv.org/abs/0906.0681

 

[dm4b]

We're talking about possible interpretations of a possible experimental result. I am expressing the view that the first thing to consider is that photons have a tiny mass, similar to neutrinos. On this assumption, there are possibly no experiments counterfactual to the assumption, and SR/GR are not affected.

Of course this isn't the only possible interpretation. All this is premature anyway, since I really doubt this will be confirmed.

I agree. I doubt this will be confimed too.

But, if it was, I think it would indeed have effects for SR and GR.

As you stated earlier:

There would be a race to determine the mass of the photon. It would be a huge surprise, but I think it would be a bigger hit for QED than SR or GR - the latter rely only on the fact that there is a spacetime structure speed limit. Whether a particular particle reaches it is irrelevant.

SR (and GR) also rely on the fact that there is a "spacetime structure speed limit", which happens to be c. There is an entire (lorentz) invariant framework within SR, EnM, GR (and, as you allude to, the Quantum Field Theories) that ties back to the metric and the speed of light. c helps us to define the spacetime interval and sets up a connection/relation between space and time. According to our theories, it is massless particles that move at c, and only massless particles.

All the amazing predicitons of relativity like the relativity of simultaneity are hinged on this invariant framework and intimately ties back to the invariant speed of light. If photons had mass they would no longer have an invariant speed to all observers. Even if the differences were outside (our current) detection range, it would still spell trouble for the theoretical framework of these theories and the precise mathematical predictions they make.

Take Einstein's old thought experiment of the photon traveling upwards in a gravitational field as compared to one traveling in an accelerating rocket. This thought experiment is used to demonstrate the equivalence principle (via equivalent redshifts, etc). Seems to me this would be effected by photons having mass, since part of it hinges on the fact that photons cannot slow down as they travel upwards in a gravitational field and therefore experience a loss in wavelength (i.e. are redshifted) instead. Again, it doesn't matter how small the effect would be, just the fact that it is there at all, would spell trouble.

Also, if photons turned out to have mass, you can also then question if whether or not the >c neutrinos also have a mass, albeit a very tiny mass smaller than our now mass-laden photons and out of our detection range. One could even begin to ask if there are any massless particles at all? (especially since we had it so wrong with the photons.)

In addition, it would open up the possibility that photons are susceptible to time-dependent phenomenon, similar to how neutrinos experience oscillations, or transform from one type of neutrino into another. Clearly, we haven't observed anything indicating this, so it may not be the case, but it would no longer be excluded as a possibility.

I think the whole thing would open up a bag of worms, really.

 

[James Leighe]

I think we could gently fit in a photon mass.

There would still be some limit of speed for massless particles, if there are any, and any formulation that was based on that would survive.

We would probably have not noticed the effects of photons having mass since it would have to be very small, like some light moving faster than other light.

 

[dm4b]

I think we could gently fit in a photon mass.

There would still be some limit of speed for massless particles, if there are any, and any formulation that was based on that would survive.

Isn't this forgetting about the connection between EnM and SR, though. I think that connetion pretty much says the photons of EnM have to be the massless particles of SR. The "c" in SR cannot apply to a particle with mass, or the invariance is lost, and the whole theory goes to cr@p.

 

[Dale]

Isn't this forgetting about the connection between EnM and SR, though. I think that connetion pretty much says the photons of EnM have to be the massless particles of SR. The "c" in SR cannot apply to a particle with mass, or the invariance is lost, and the whole theory goes to cr@p.

There needn't be any massless particles at all for SR to be valid. Also, SR is compatible with tachyons (not implying that neutrinos may be tachyons). I would think that either causality or the 0 mass of a photon would be more at risk than SR from a confirmation of this result.

That said, I would really like to see the actual scientific publication rather than a pop-media report.

 

[Dale]

any non-zero mass must be accelerated from zero velocity to move

This is not strictly true. When a particle is first created in a nuclear reaction it will generally have some non-zero initial velocity. That said, regardless of the initial velocity you are correct about the energy requirements to accelerate it further, but they are not claiming faster than c, only faster than light. The implication being that light doesn't travel at c.

 

[dm4b]

There needn't be any massless particles at all for SR to be valid.

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?

 

[JordanL]

This is not strictly true. When a particle is first created in a nuclear reaction it will generally have some non-zero initial velocity. That said, regardless of the initial velocity you are correct about the energy requirements to accelerate it further, but they are not claiming faster than c, only faster than light. The implication being that light doesn't travel at c.

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

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

 

[James Leighe]

It would be a small enough mass that our measurements would not be accurate enough to detect those minuscule effects.

 

[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.