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CERN team claims measurement of neutrino speed >c

  1. Sep 22, 2011 #1


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    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" [Broken]
    3. The previous posts in this thread

    And original post:

    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 [Broken]
    Last edited by a moderator: May 5, 2017
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  3. Sep 22, 2011 #2


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    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.
  4. Sep 22, 2011 #3
    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.
  5. Sep 22, 2011 #4


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  6. Sep 22, 2011 #5


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    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.
  7. Sep 22, 2011 #6
    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.
  8. Sep 22, 2011 #7


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    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.
  9. Sep 22, 2011 #8
    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.
  10. Sep 22, 2011 #9


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    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.
  11. Sep 22, 2011 #10
    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...
  12. Sep 22, 2011 #11
    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.
  13. Sep 22, 2011 #12


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    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.
  14. Sep 22, 2011 #13
    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.
  15. Sep 22, 2011 #14
    Here is the msnbc story:
    http://www.msnbc.msn.com/id/44629271/ns/technology_and_science-science/" [Broken]
    It seems that the measurement team is asking for confirmation, so don't be too hasty.
    Last edited by a moderator: May 5, 2017
  16. Sep 22, 2011 #15
  17. Sep 22, 2011 #16
    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.
  18. Sep 22, 2011 #17


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    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.
  19. Sep 22, 2011 #18
    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.
  20. Sep 22, 2011 #19
    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.
  21. Sep 22, 2011 #20
    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.
  22. Sep 22, 2011 #21
    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!
  23. Sep 22, 2011 #22


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  24. Sep 22, 2011 #23
    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:

    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.
  25. Sep 22, 2011 #24
    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.
  26. Sep 22, 2011 #25
    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.
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