Tag Archives: OPERA

Finally An OPERA Plot that Makes Some Sense

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:

http://www.faz.net/aktuell/wissen/physik-chemie/interview-ueber-die-moeglichen-fehlerquellen-messfehler-koennten-ueberlichtgeschwindigkeit-erklaeren-11660876.html

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: Continue reading

Everybody’s a Critic

I wanted to make a few assorted comments about the OPERA experiment’s painful climb-down, and about yesterday’s widespread response to it, which bothered me a lot.  You may want to read my initial post from yesterday, and also my attempt to sharpen the main question OPERA left unanswered in my second post.  [ALSO: look ahead to the next post, in which many of the confusions that were still present at the time of this post were resolved.]

Over the past day I’ve learned enough to be pretty convinced (but not certain) that the situation that we are in is case (e) [or a version of case (d)] as described in yesterday’s post: that probably the previous OPERA experimental data is tainted and we can draw no conclusions from it at all.  It’s not that they found a problem that shifts their data so that it is consistent with Einstein’s relativity [case (b) from yesterday], and they can say that the neutrinos travel as expected.  (Press reports that said so are just wrong.) It’s that they found a problem that means their data from last year can’t be interpreted at all… at least, not at the moment, and maybe not ever.  If true, this would indeed mean that there is no longer any data from OPERA that can be used to measure neutrino speeds to good accuracy, and we’re back where we were before OPERA ran in the first place: with no reason to think there’s anything amiss with Einstein’s relativity equations.  As for OPERA, the only way forward is to rerun the experiment (apparently in March-April-May.)

[The NY Times article that appeared today (which attributes OPERA, a non-CERN experiment, to CERN; what has journalism come to these days?) has some additional details, but if you read it carefully, those details don’t change anything written in this post.  See the first comment at the very end of this post.]

Ok, some comments. Continue reading

Synopsis of the OPERA Situation

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.

OPERA in Question

[UPDATE: Some extensive comments added below.]

[UPDATE: Journalists and Bloggers: PLEASE NOTE: OPERA is not a CERN experiment.  The CERN laboratory does not deserve the bad press it is getting (though they certainly unwisely put themselves in a position to receive it.)]

Many of you are probably already aware of various rumors running around By now you are all aware of yesterday’s initial report that the OPERA experiment — famous for announcing that neutrinos traveling from CERN to the Gran Sasso Laboratory in Italy arrived 60 nanoseconds (billionths of a second) earlier than expected, thus suggesting that neutrinos can travel slightly faster than the speed of light — had found a problem with a cable connector that exactly explains the 60 nanosecond timing shift.

But the immediate source of this rumor was a science journalist, and the article was based on an anonymous source who is not described as being in the OPERA experiment. And the details quoted in the article didn’t add up, in my view. Given the number of wrong reports and rumors that I have read over the past months about this experiment, my reaction was to wait.

I didn’t have to wait long. Presumably Perhaps to avoid misinformation from hitting the headlines, it appears that OPERA has released a statement  that indicates that the article from earlier today yesterday is not true. [Update: To be clearer, I probably should have written, “true in its details.”]  But this statement itself contains big news. Continue reading

OPERA’s Next Act

Can’t take a breath this week without stumbling over another particle physics result of note. (It isn’t usually like this, folks — this year has been very odd.) OPERA (the experiment that claims their neutrinos travel faster than light does, which if true would require some kind of modification of Einstein’s relativity principles) is back, and they’ve done a very important cross-check many of us were hoping they would do, which is very good news indeed. Since they say that it confirms their previous result, the plot now thickens considerably; the experiment’s technique is now harder to question, and the long list of possible sources of problems with the experiment is considerably shorter. Obviously this news deserves a long post, explaining exactly what they did and why it is such an improvement. I’ll produce one for you before the weekend is over, possibly as soon as tomorrow. Watch this space!

In the meantime, here’s a guide to past posts, which cover most of what you need to know: Continue reading