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CERN team claims measurement of neutrino speed >c 
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#19
Sep2211, 04:08 PM

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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 wellestablished 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. 


#20
Sep2211, 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 onesixth 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. 


#21
Sep2211, 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! 


#22
Sep2211, 04:31 PM

Sci Advisor
P: 8,317

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 


#23
Sep2211, 04:37 PM

P: 317

But, if it was, I think it would indeed have effects for SR and GR. As you stated earlier: 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 massladen 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 timedependent 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. 


#24
Sep2211, 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. 


#25
Sep2211, 04:45 PM

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#26
Sep2211, 04:49 PM

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


#27
Sep2211, 05:12 PM

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#28
Sep2211, 05:12 PM

P: 317

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? 


#29
Sep2211, 05:15 PM

P: 42

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


#30
Sep2211, 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.



#31
Sep2211, 05:19 PM

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#32
Sep2211, 05:21 PM

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#33
Sep2211, 05:24 PM

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#34
Sep2211, 05:30 PM

Sci Advisor
P: 1,677

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. 


#35
Sep2211, 05:47 PM

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