I’m a little torn about this: the Twitter machine and other social mediums have blown up about this story at Science Express, which claims that the faster-than-light neutrino result from the OPERA collaboration has been explained as a simple glitch:
According to sources familiar with the experiment, the 60 nanoseconds discrepancy appears to come from a bad connection between a fiber optic cable that connects to the GPS receiver used to correct the timing of the neutrinos’ flight and an electronic card in a computer. After tightening the connection and then measuring the time it takes data to travel the length of the fiber, researchers found that the data arrive 60 nanoseconds earlier than assumed. Since this time is subtracted from the overall time of flight, it appears to explain the early arrival of the neutrinos. New data, however, will be needed to confirm this hypothesis.
I suppose it’s possible. But man, that would make the experimenters look really bad. And the sourcing in the article is just about as weak as it could be: “according to sources familiar with the experiment” is as far as it goes. (What is this, politics?)
So it’s my duty to pass it along, but I would tend to reserve judgment until a better-sourced account comes along. Not that there’s much chance that neutrinos are actually moving faster than light; that was always one of the less-likely explanations for the result. But this isn’t how we usually learn about experimental goofs.
Update from Sid in the comments: here’s a slightly-better-sourced story.
Update again: and here is the official CERN press release. Not exactly admitting that a loose cable is at the heart of everything, or even that the result was wrong, but saying that there were problems that could potentially invalidate the result.
The CBC story is better sourced though the CERN spokesman mentioned at the end only says that “a flaw in the GPS system has been found” and doesn’t go into details.
http://www.cbc.ca/news/technology/story/2012/02/22/technology-faster-than-light-neutrinos.html
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Well, it was fun while it lasted. And the next time someone that I’m giving tech support to tells me I’m being silly when I ask them if they checked their cables……………………..
Of course, everyone knew that there had to be some glitch somewhere. If it is too strange to be true, it is not true. Sort of reminds me of the 17 keV neutrino.
Only ~230 citations for the original paper.
It’s going to be really really tough to get a 60ns delay out of a bad fiber optic connection. They either work or they have high error rates. Assuming 100M bits per second cable (i.e. 125MHz), that’s a lot of bits to store away somewhere.
Indeed if this is true, that it was all due to a faulty cable, then what a HUGE embarrassment it will be to the whole OPERA team. And they will have no-one to blame but themselves, since they put out a press-release on this result in the first place.
The official statement from the collaboration:
“The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock.
These two issues can modify the neutrino time of flight in opposite directions.”
http://blogs.nature.com/news/2012/02/faster-than-light-neutrino-measurement-has-two-possible-errors.html
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Highly Technical Question: would it have been possible to check the cables BEFORE putting the paper on the arxiv? Another question: why the rush? Who were they trying to beat?
I believe Discover Magazine made FTL neutrinos its #1 Science Story of 2011.
This one will make a lot of people look bad.
“But man, that would make the experimenters look really bad.”
what would it make the theorists (who deluged us with so much garbage) look like ?
Don’t worry, #12, extra dimensions will be just fine.
60 nanoseconds is a huge cable error, equivalent to about 10 meters of cable. It is possible that there was some internal reflection in the loose cable which caused such a big error, but I suspect that the real problem was the system latched onto the trailing edge of the 1 pps timing signal – this is more likely to happen when something (like a bad cable) is screwing up the timing pulse, and it can cause a considerable excess delay (order 100 nanoseconds or more). In many systems the width of the 1 pps pulse is not controlled, and so it will vary. This leads to the common symptom of this problem – the timing becomes erratic at the nanosecond level. If such timing is used in VLBI (for example) then the extra noise is pretty noticeable.
If something like this was the cause of their error then they deserve the bad PR they will get, as they really should have included a timing professional as part of the experiment (as opposed to a consultant role). I have had several discussions with timing professionals about the superluminal neutrino results, and each time the trailing edge issue has come up.
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If only they had done this the first time ’round… .
According to Carl Brannen, “It’s going to be really really tough to get a 60 ns delay out of a bad fiber optic connection.” There are 3 basic possibilities for explaining the OPERA neutrino anomaly:
1. There are one or more serious experimental errors.
2. Neutrinos are travelling faster than the speed of light in a vacuum.
3. Photons are travelling slower than general relativity theory predicts.
I call the Rañada-Milgrom apparent-or-real effect the apparent or real necessity of replacing the -1/2 in Einstein’s field equations by -1/2 + sqrt((60±10)/4) * 10**-5.
http://en.wikipedia.org/wiki/Pioneer_anomaly
http://arxiv.org/abs/gr-qc/0410084 “The Pioneer anomaly as acceleration of the clocks”
http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
The OPERA neutrino anomaly confirms the Rañada-Milgrom effect. The flyby anomalies, NASA’s Gravity Probe B, and the Sachs-Wolfe effect also confirm the Rañada-Milgrom effect. The empirical evidence shows that general relativity theory is slightly wrong.
You ever actually do an experiment Sean? Bad cables are common, optical fibers merely allow new failure modes. New experiments often introduce new failure modes.
In Hell’s Kitchen (NYC) Says:
“But man, that would make the experimenters look really bad.”
what would it make the theorists (who deluged us with so much garbage) look like ?
Like theorists. That’s what they do, try and make sense of new experimental results, and there is nothing wrong with it, even if those results later turn up short.
Really, did anyone actually expect this anomaly to turn out differently?
There are hundred of ways that OPERA could have got this wrong, and almost all of them are embarassing. The odds were always high that this was a trivial mistake.
Holy shit. You make a valid point on how these people look.
Well, there goes one day I thought I wasnt wasting. Sean, you insipire rage out of me. 😀
Why is it any worse than bad connections for magnets at the LHC or a bad mirror on the Hubble telescope, or crashing a spacecraft because somebody didnt convert inches to centimeters ? Heck – a long time ago a new release of unix broke my rs232 code. Oh well – the wonders of technology.
@Carl Brannen
“It’s going to be really really tough to get a 60ns delay out of a bad fiber optic connection.”
Don’t assume it is ATM, Ethernet or the such. It might simply be a “home-made” connection to transmit information via a fiber optic cable and a simple pulse of light.
A loose cable could attenuate the signal. Then a non-linear rise of the signal in the transmitter (and we are talking about real life transmitters, not a theorized ideal source), combined with the threshold of the receiver => Delayed signal.
In that case, they should have you used a pulse and sampled both flanks…
@David Brown
What the heck are you talking about?