Ok, thanks to a commenter (Titus) to this morning’s post, I learned of information available in the German language press that is vastly superior to anything I had seen previously— much better than today’s New York Times article, because it contains detailed and extensive quotations from a participating scientist on OPERA. [There is nothing like (nearly) first-hand information!] Here is the link:
You can try Google translate and it isn’t awful, but it does contain some important mistakes; my German is good enough to read some more of it but not good enough to do a proper translation for you. I encourage someone fluent to help us out with a proper translation. Someone has done so — see the first comment. [Thanks to the translator!] [2/26 UPDATE: New comment on the situation added at end of post.]
Facts that one can glean from this article bring me to the following conclusions:
As I suspected all along (and contrary to the original press reports), the OPERA experimenters do not claim to have found the cause of the 60 nanosecond shift in the timing of the neutrinos. They only have suspect causes. This is not the same thing. The mystery is not over yet (though it has probably entered its final chapter.) [UPDATE: In fact, there’s something very weird here. See comment at the end of this post.]
The situation is complex, because they know of two problems, one (with an oscillator) decreasing the shift and one (with a fiber) increasing it. We now know (thanks to the German article) that both of these effects are tens of nanoseconds in size, and one (the one involving the famous faulty fiber) could be as large as 100 nanoseconds. That means that in the language of yesterday afternoon’s post, whose Figure is reproduced here, the situation with OPERA is perhaps describable as case (d), perhaps as case (e). [The difference is whether you take your knowledge of what may have gone wrong as a large systematic uncertainty — giving (d) — or you say that you don’t know enough to do that properly — which gives you (e). They seem to be somewhere in between right now; they know enough to give something like (d), but are focused on reducing the uncertainties down toward (c) or better before they give a quantitative statement.] In short, it is now confirmed that there currently is no known discrepancy — not even a weak one — with Einstein’s theory of relativity.
Despite all of the jokes and snide remarks, it sounds as though the problem with the fiber was quite difficult to find, and was a really nasty one: it depended very sensitively on exactly how the fiber
was screwed in [thanks to improved translation] was oriented , which means a defective fiber or a defective connection, I guess. We’re not just talking about an ordinary loose wire. This is not inconsistent with what my experimental colleagues tell me about looking for sources of electronics problems; in particular, note the comment (highlighted in red) from this morning’s post. [Also note some of the comments coming in; we’re still learning about whether this failure mode was a subtle one or would have occurred early on to someone with the right expertise.]
The experimenters believe that over the coming weeks they can, with some considerable effort, nail down to some degree how big these two effects were. If they succeed, perhaps they will be able to bring case (d)/(e), which is what we are currently dealing with, back closer to case (a) or (b), or at least case (c). We’ll see what they say then. But no one, not even OPERA, will be very confident in the result at that point.
OPERA cannot be absolutely sure that they have found the cause of the timing shift in the neutrinos — and that there are no other major problems — until they rerun the experiment, to see whether fixing the two problems changes last year’s result by just about 60 nanoseconds. Apparently this is not something they can tell post facto just by looking at the way the fiber and the oscillator behave now; it is still not entirely clear why, but surely the devil here is in the details, and we won’t get those from press articles.
Apparently there are people within OPERA who argued back in September that the result was not ready for public presentation. They are vindicated now.
Several experiments (OPERA, ICARUS, BOREXINO, and apparently another one I didn’t know about, LVD) will all attempt the neutrino speed measurement, independently but simultaneously, this spring. (The neutrino beam is very wide when it arrives at the Gran Sasso laboratory, and all of the experiments sit inside it.) Hopefully OPERA will have eliminated its problems, and the other three experiments will not make any mistakes, and all four experiments will get the same answer. Of course these are very hard measurements, so they might not get the same answer. We’ll see. If they all find no shift, then we’re all happy with Einstein and the story is over. If only OPERA finds a shift, and it is still 60 nanoseconds (or comparable), then we’ll know the OPERA folks still haven’t found the source of their problem. If all the experiments find the same non-zero shift, we’ll start talking about Einstein and relativity again… but don’t hold your breath.
UPDATE: There’s something that’s been bothering me all along, and although I alluded to it in an earlier post, a commenter’s question prompted me to write it down more carefully. This issue must also be bothering the OPERA people a lot.
The point is this: there is no reason that the two problems that OPERA has identified — that an oscillator in the main clock was off from what it had been measured to be at some earlier point — and that the exact orientation of the optical fiber bringing in the GPS timing signal could change the amount of light entering the optical-to-electrical conversion system and somehow [they know how, but I don’t] induce a delay in the electrical timing signal exiting the system — should be constant in time, at least not over years. They measured the oscillator at some point and it was fine; now it isn’t. When did it shift? And can we really expect that the orientation of a cable would remain fixed over the three years during which the original OPERA experiment was carried out? A little bit of maintenance, or even just a little settling of other wires nearby, would easily lead to a change in the cable’s orientation.
The mysterious thing is that the two versions of the OPERA speed measurement — the one with long pulses that was done over 2009, 2010, and 2011, and the one with short pulses done over two weeks in October 2011 (which I called OPERA-1 and OPERA-2 to distinguish them) — gave the same answer, about 60 nanoseconds early arrival. But if the problem came from a slowly drifting or suddenly shifting clock combined with a fiber that slowly drooped or got jostled at some point, you’d expect OPERA-1 to have an average of different timing shifts as the oscillator and fiber changed from 2009 to 2011, and OPERA-2 to have a single timing shift that represented what the oscillator and fiber were doing in October 2011. There’s no reason the average timing shift over three years should be the same as the final timing shift, unless the timing shift was extremely stable — but the two problems they’ve identified suggest instability would have been expected.
This certainly has me [and some commenters] wondering (and I am sure it has the OPERA people wondering) whether they’ve actually found the main problem.