CERN team claims measurement of neutrino speed >c

  1. turbo

    turbo 7,366
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    Edit:

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


    1. The PF Rules. 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:

    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
     
    Last edited by a moderator: Sep 24, 2011
  2. jcsd
  3. PAllen

    PAllen 5,797
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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. 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. turbo

    turbo 7,366
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  6. PAllen

    PAllen 5,797
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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. 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. PAllen

    PAllen 5,797
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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. 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. PAllen

    PAllen 5,797
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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. 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. 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. turbo

    turbo 7,366
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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. 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. Here is the msnbc story:
    msnbc
    It seems that the measurement team is asking for confirmation, so don't be too hasty.
     
  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.
     
  17. PAllen

    PAllen 5,797
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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.
     
  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.
     
  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.
     
  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.
     
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