Of Particular Significance

Synopsis of the OPERA Situation

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 02/23/2012

I thought I’d better try to clarify what the logical issues are regarding OPERA before things get too confusing.  [Read the previous post first.] What’s going on is sketched in the Figure below.

a) In September (and confirmed in November) OPERA claimed to have found that, compared to expectations, neutrinos from CERN seemed to be arriving early, by about 60 nanoseconds, with a six sigma significance.  That is sketched in the figure as a bar, centered at 60 nanoseconds, with a width of 10 nanoseconds in each direction (so if you made the bar six times larger its bottom would reach zero nanoseconds.)    Such a result is convincing — convincing that either they made a mistake or they’ve discovered a new effect in nature.  The new effect in this case — neutrinos going faster than the universal speed limit — is very implausible for many reasons that I’ve covered in the past, but such an experimental result cannot simply be ignored.

(a) What OPERA said originally. (b) What yesterday's newspaper article claimed OPERA was now saying. (c),(d),(e) Three possible interpretations of OPERA's statement. In each case, a bar whose center lies at the most likely result of the measurement, and whose width indicates the degree of uncertainty, is shown. If we take OPERA's statement at face value, we still don't know if it is inconsistent with zero but less certain than before, consistent with zero, or simply unknown (in which case the previous measurement must be discarded.)

b) On February 22nd, a news report said that OPERA had found a mistake — a problem with the connection in an optical fiber — that explained the 60 nanosecond shift.  That would mean that the result was now — with confidence — consistent with Einstein’s relativity.

But the OPERA statement contradicts b).  Unfortunately it doesn’t clarify whether we have the situation c), d) or e):

c) The uncertainty on the result is larger than it was before, although the result is still not particularly consistent with what you would expect from Einstein’s relativity.  However, the reduced confidence in the result would mean that instead of it being an impressive result it would become a much less impressive one, much easier to ignore.

d) The uncertainty on the result is so much larger than it was before that the result is actually consistent with Einstein’s relativity, though so weak that it can’t distinguish at all between zero and the original non-zero value that OPERA claimed.

e) There is no sensible estimate of the uncertainty on the result. The result simply cannot be used and will have to be discarded.

From the point of view of the plausibility of the original OPERA result, (b), (c), (d) and (e) are all bad.  From the point of view of the experiment’s credibility, though, case (b) would look the best: the experimenters could at least say that they figured out what they did wrong and knew what it was.  Cases (c), (d) and (e) are increasingly bad; they indicate less and less knowledge of how their own experiment worked.  [But see the first comment below, which criticizes the way I expressed this, and emphasizes that a lack of knowledge is not always the fault of the experimenters.]  However, the situation might change over time; right now they might be in case (d) [because they’re still working on understanding what happened] but soon it might switch to case (b), or back to case (a), once they have it straight.  So we do have to let things play out a little bit, and not jump to conclusions.

But I think it is clear we are not currently in case (b).  Because if we were, why would one would emphasize the re-running of the experiment?  There would be no need.

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27 Responses

  1. P.S. :Dear Friends : let me clarify ; my question has nothing whatsoever to do with any quantum gravity speculation, be it M or LOOP or what maybe, i am just asking : suppose that tomorrow 2/25/2012 the graviton is discovered with its mother field be it quantum or whatever , then it was confirmed that gravity IS field+particle , does this demolish the concept of gravity as geometry ? ( noting that the later is not a physical ontological fact but mere mathematics and a very good mere indeed , as some physicists are not happy with space as a real physical thing.) , and if it does not demolish then why? how can we translate geometry to field+particle?
    This is a fundamental question that needs answer as human mind can conceive a solution but conception IS NOT ontology.

    1. Hi aa.sh 😉
      If You are very curious about the importance of geometry (and mathematics in general) in fundamental physics, You may read this nice book: http://www.amazon.com/Shape-Inner-Space-Universes-Dimensions/dp/0465028373
      Somewhere in the last part, the mathematicien Shing-Tung Yau explains that the notion of geometry as we know it breaks down around the Planck scale (if I remember this right) and should be replaced by quantum geometry, which is still under conctuction …

      I`m not so familiar with the notion of “ontology” and honestly speaking I dont like this word too much because it usually goes together with confusion about quantum mechanics … ;-P


  2. TO both friends , Matt. and Dilaton : forgive me , but i am not talking about scientific description , i mean that ontologically G.R. description is far from identical with Q.M. one ……in the former we have geometry , in the later we have field and particle…..if the graviton is the messenger particle mediating the effect of “” getting close”” then geometry has no meaning, am i right ?

    1. Hi aa.sh 😉
      (I hope writing from here, this comment does not get lost :-)…)
      If You are very curious about the importance of geometry in fundamental physics, You can read this nice book: http://www.amazon.com/Shape-Inner-Space-Universes-Dimensions/dp/0465028373/ref=sr_1_1?ie=UTF8&qid=1330088983&sr=8-1 … Somewhere in the last part, Shing-Tung Yau explains that geometry as we know it breaks down around the Planck scale (if I remember this right) and should be replaced by quantum geometry which is still under construction.

  3. Sounds to me like a textbook case of accuracy versus precision.

    Tracking down the measurement uncertainty would make a great project or two.

    Below are some project suggestions based on my experience working with 50GHz clocks and data. It has been a while since I worked on these problems, but as far as I know they are still open.

    Chase down polarization mode dispersion in single mode fiber and connectors. Show how stable fiber cable optical length really is. The single-mode fiber I have used would not be so great in a physics experiment. Do physicists have something better than communication fiber and FC connectors? If not, this could cause an accuracy problem.

    Track down the agreement between the integration of phase noise in the frequency domain and jitter in the time domain of high-speed (50GHz or so) clocks in modern test equipment. Last I measured it, it was off by about a factor of 2. This could reflect a precision problem. For example, in my case I suspect the time domain result was showing less jitter than was really present. But as a spectrum analyzer guy I tend to trust them more.

    Clock signals and data signals have different types of jitter errors. Find the sources of these error differences and show how to control them. There are several known reasons for the differences, but as far as I know the prediction of the details of these differences in specific circumstances is still mostly unknown.

  4. HI MATT. , HI all friend ; As we are in the territory of Dr. AINSTEIN , i have a very real problem—for me at least–that is : If gravity waves are proved to exist as a quantum field , and if the graviton is discovered, then my friends, what about the primary equation of G.R.: mass/enery distribution in space =configuration and geometry of that space…do we have here a basic contradiction?
    I really want to know…….help needed.

    1. The right quantum gravity should converge to general relativity in the classical limit, so there is no basic contradiction between the two descriptions of gravity You mentioned.

  5. Matt is always fair and honest in his judgment, and this is the value of this blog.

    Physics is a science of listening to the Nature. Yet, there are two ways to listen. One is doing experiments, seeing what the Nature reveals to us. However, this way is a bit tricky. What we are seeing might not always be the true color. In this OPERA case, the result might be contaminated with system errors. Yet, the seeing act itself might alter the original color, and we know this all too well in Quantum Mechanics.

    However, the Nature does tell us its true color via its “own statements,” often different from a particular experiment. For example, proton definitely has a perfectly defined internal structure regardless of its appearances during our seeing acts (via different experiences). Nature tells us this fact with the fact that all protons are identical for the external world. With this Nature’s statement, the apparent complexity of the proton’s internal structure must not arise from its essential internal structure but must be caused by a different reason. For two identical kaleidoscopes (with identical internal structure and identical colored beats), they will give out completely different images. Even the same kaleidoscope will give out different images in its time evolution. The complexity does not arise from its internal structure per se but arises from its void space which allows the random movements of those colored beats. On the same token, the apparent internal structure complexity of proton gives the hints about the space-time sheet structure “inside” of proton.

    For this Superluminal Neutrinos issue form OPERA experiment, the Nature might have made a statement about it too.

    There is a theoretical calculation for alpha (electron fine structure constant) available online, and I am quoting it below.
    Beta = 1/alpha = 64 ( 1 + first order mixing + sum of the higher order mixing)
    = 64 (1 + 1/Cos A(2) + .00065737 + …)
    = 137.0359 …

    A(2) is the Weinberg angle, A(2) = 28.743 degrees
    The sum of the higher order mixing = 2(1/48)[(1/64) + (1/2)(1/64)^2 + …+(1/n)(1/64)^n +…]
    = .00065737 + …

    The above calculation did use Weinberg angle (a key parameter in particle physics) as a key parameter. However, it does not include the “c” (light speed) in its calculation, that is, without putting the “c” in it first. Yet, the formula of alpha does carry c (light speed),
    Alpha = e^2/c * h-bar .

    Thus, if (a big if) this theoretical calculation of alpha is a fact of Nature, then the light speed is guaranteed as the causal speed limit by this alpha. Then, even if the OPERA experiment were confirmed, it will not change the fact that there is a causal speed limit (guaranteed by alpha) and that light travels at that limit. That is, the OPERA result must be caused by a different reason, similar to the complexity of kaleidoscope’s images.

  6. my comment was not published, therefore it would appear the moderator does not like my replies… 🙂 Is the moderator the same as the publisher of this blog ?

    1. sorry! just an oversight. Too many comments, I missed yours; thanks for alerting me. I only delete or edit comments that are nasty or that contain a ridiculous amount of advertising of false information. But sometimes I am a little slow, miss one, or lose one in a spam filter; you are always welcome to ask about a missing comment.

  7. For all it’s worth, I encountered a strange situation yesterday. I had lost a few TV channels on my (high speed internet plus) TV connection. Reception was perfect on most channels, but on others, it was indicated “this channel to be available shortly”. After checking out all other possibilities, the Cable Company technicians told me they had encountered that situation before, and would I please screw every cable connection tight.
    It turned out that the input cable in the TV box had become slightly loose from thermal cycles. So there was a complete loss of some channels, while other High Definition digital channels were left completely unscathed. I would never have expected such a thing. But then I remembered that Hans Solo had to kick his spaceship to get it to achieve Faster Than Light while he was fleeing the Dark Side’s plutocrats during Star Wars. Sophisticated we are, yet the basics stay OPERAtive…

  8. Case (e) doesn’t necessarily imply the experimenters don’t adequately understand how their own experiment worked. For instance it could be they found a flaky connection, one that distorted or killed the signal it was supposed to transmit in an essentially unpredictable way. (E.g. if you stress the fiber up, down, left, right, the signal changes erratically.) If that’s the case there might be no way to know how or if the signal was affected during past data taking.

    1. Agreed; I did not word this as well as I might have. Indeed, I suspect that what you describe is what happened. But the problem is that this is the worst case for credibility, even though it could happen to anyone. “What do you mean”, people will say, unfairly, “that your data is completely useless and you have to start from scratch?” And they will say, perhaps more fairly, “Why didn’t you figure that out before you made such a big deal about your result?”

      How might you suggest this kind of problem be better explained to the public? Do you know of some good historical examples where a similar effect has tripped up first-rate experimenters?

  9. Dear Dr. Matt Strassler:

    We will put another comment in the Neutrino problem. As we accomplish with all the rules posting comments in the Blog, if you continue to make illegal censorship, in an act similar to Inquisition, we will contact the authorities of the University and WordPress telling the illegal action as you, as auto-called scientist, are doing.
    Best wishes.
    Lucy Haye
    SAA’s representative

    1. No, you do not follow rules. You insult me and my colleagues every time you write. You never make comments; you make statements, each of which is factually wrong and foolish. You advertise your own viewpoints with links to false ideas in every post. Every one of these would be grounds for deletion. This is not a wide-open public forum where you can post whatever you want. It is a forum to explain the mainstream ideas in science. You don’t have to believe in the mainstream ideas in science; it is a free country. And you can post whatever you like on your own website and your own blog, and I’ll defend your right to do that. You can try to convince whoever you can however you want to on your own website. But you have no right to damage my website. Go ahead and contact the University and WordPress; go right ahead.

    2. If I were not banned (maybe righly so …), I would recommend to Lucy Haye to better stop insulting and threatening Prof. Strassler, who does a beautiful job in informing a broader interested public about what is going on in particle physics and related fields.
      I am glad to see that he has finally started to defend and protect himself and his colleagues against trolling attacks of people like Lucy Haye and other spoiler, who try to spoil and mess up with his good work !

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