Of neutrinos and systematic errors

October 14, 2011

Since the surprising ‘discovery’ of faster-than-light neutrinos was announced a few weeks ago, quite a few people have brought the topic up in conversation with me. My response has been that the experimentalists, despite their diligence and expertise, have undoubtedly overlooked a systematic error in their analysis, and that the ‘finding’ will go away when the experimental method is analyzed more closely.

Earlier this week an interesting paper was published by Ronald van Elburg of the University of Groningen that seems to be exactly the sort of thing I was expecting. He argues that the experimentalists overlooked a subtle relativistic effect that affects the synchronization of the clocks used to measure the speed of the neutrinos. His back-of-the-envelope estimate for the resulting error is almost exactly what is needed to bring the neutrinos velocity back below the speed of light where it belongs.

The paper is short and not hard to read. An even more accessible summary can be found here. I like the way the summary concludes:

If it [the proposed explanation] stands up, this episode will be laden with irony. Far from breaking Einstein’s theory of relatively, the faster-than-light measurement will turn out to be another confirmation of it.

Exactly so. It would be nice if this turned out to be the answer to the riddle.

14 Responses to “Of neutrinos and systematic errors”

  1. Vince Says:

    Cohen and Glashow also came out with a paper showing that if neutrinos really did travel faster than light, and at the speed found by OPERA, they would have lost a lot of energy to electron-positron pair production. This energy loss was not observed by OPERA.

  2. cburrell Says:

    I heard about that paper, Vince, but I had not had time to look at it yet. A friend at the CERN theory division remarks that they were going crazy pumping out papers. You know how it is: everybody has a pet theory to account for an anomaly, and they’ll write the paper even if they don’t believe the anomaly is real. But Cohen and Glashow’s contribution sounds like a substantive one: cool down, folks.

  3. Vince Says:

    Yes, I noticed a plethora of papers in hep-ph about OPERA’s result. Are you talking about Michael Trott? He was my 1st year physics TA and he gave a talk at U of Texas at Austin earlier this past spring, which I attended. It’s not my field (I’m in GR), so I didn’t understand most of the talk, just the beginning, but it was cool to see him again.

  4. cburrell Says:

    The very same. It’s a small world!

  5. KathyB Says:

    This joke appeared in the Post last week:

    “Sorry, we don’t serve faster-than-light particles in here” said the bartender.
    A neutrino walked into the bar.

  6. Christina A. Says:

    Frankly, it’s been a toss-up between hearing your opinion on this physics stuff and what’s happening with your home renovation.

    Glad to hear at least the theoretical physics side.

    Just came on tonight to backtrack your Breaking Bad / The Wire posts as I am now a few episodes into BB. Already addicted.

  7. cburrell Says:

    We’ve been meaning to call, but the renovations have kept us up till the wee hours each night this week. We’re pulling down the back porch this morning. Taking pictures.

  8. Vince Says:

    Another source for interesting lectures by a variety of professors.


  9. cburrell Says:

    Very nice. Strings!

  10. Vince Says:


    In case you’re interested, here are Sean Carroll’s CERN Lectures on Cosmology and Particle Physics:


  11. cburrell Says:

    Thanks very much, Vince. Those look good. He’s a good lecturer. I will try to find the time to watch them.

  12. cburrell Says:

    I watched a good piece of the first lecture last night, and I am going to try to continue with them. The presentation is good and clear.

    One thing he said has me perplexed. I had thought that in an expanding (approximately) FRW universe, the distance between any two points would contain dependence on the scale factor a, and so would change as the universe expands. He said this was not true, but that certain regions ‘decouple’ from the expansion, so that there is no longer any dependence on the scale factor. I do not really understand why.

    Is it that the inhomogeneity and non-isotropy of our local neighbourhood causes us to decouple from the FRW metric, and so from the expansion? But what causes the inhomogeneity, etc.? An inhomogeneous distribution of matter. So is the claim that certain distributions of matter can arrest the expansion/contraction of the spacetime in which they exist? I suppose that is not so strange…

  13. connector Says:

    According to this scientist Janet conrad, the full sentence should be…faster than the speed of light in a medium http://youtu.be/CBfUHzkcaHQ?t=54m58s ..Shrink of light effect [if I heard right] :
    “Nothing can go faster than the speed of light IN A VACCUM.” Light slows down as it travels through matter, and neutrinos,impervious to matter, are then faster than the speed of light. There is a photonic beam which is visible.

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