Register to reply

CERN team claims measurement of neutrino speed >c

by turbo
Tags: anisotropy, cern, ftl, gps, new math books
Share this thread:
kfmfe04
#19
Sep22-11, 04:08 PM
P: 36
Quote Quote by Runner 1 View Post
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
#20
Sep22-11, 04:15 PM
P: 42
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
#21
Sep22-11, 04:28 PM
P: 230
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
#22
Sep22-11, 04:31 PM
Sci Advisor
P: 8,582
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
#23
Sep22-11, 04:37 PM
P: 319
Quote Quote by PAllen View Post
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:

Quote Quote by PAllen View Post
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
#24
Sep22-11, 04:40 PM
P: 230
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
#25
Sep22-11, 04:45 PM
P: 319
Quote Quote by James Leighe View Post
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.
DaleSpam
#26
Sep22-11, 04:49 PM
Mentor
P: 17,264
Quote Quote by dm4b View Post
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.
DaleSpam
#27
Sep22-11, 05:12 PM
Mentor
P: 17,264
Quote Quote by jnorman View Post
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
#28
Sep22-11, 05:12 PM
P: 319
Quote Quote by DaleSpam View Post
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
#29
Sep22-11, 05:15 PM
P: 42
Quote Quote by DaleSpam View Post
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
#30
Sep22-11, 05:17 PM
P: 230
It would be a small enough mass that our measurements would not be accurate enough to detect those minuscule effects.
DaleSpam
#31
Sep22-11, 05:19 PM
Mentor
P: 17,264
Quote Quote by JordanL View Post
So then c would be the "speed limit", and the speed of light would be something slightly less...
Exactly.

Quote Quote by JordanL View Post
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.
DaleSpam
#32
Sep22-11, 05:21 PM
Mentor
P: 17,264
Quote Quote by dm4b View Post
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
#33
Sep22-11, 05:24 PM
Mentor
jtbell's Avatar
P: 11,771
Quote Quote by nealst View Post
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
#34
Sep22-11, 05:30 PM
Sci Advisor
P: 1,685
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
#35
Sep22-11, 05:47 PM
Admin
Borek's Avatar
P: 23,567
Quote Quote by muppet View Post
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
#36
Sep22-11, 06:30 PM
Emeritus
Sci Advisor
PF Gold
ZapperZ's Avatar
P: 29,238
Quote Quote by turbo View Post
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.


Register to reply

Related Discussions
CERN, speed of light... Special & General Relativity 6
Does neutrino oscillation from electron neutrino to muon neutrino conserve energy? High Energy, Nuclear, Particle Physics 4
Avg Speed of Relay team (x and t are not given) Introductory Physics Homework 1