Sunday, June 17, 2012

On a new discovery about the speed of neutrinos

NOTE: Update added below.

A recent article reports a new discovery about the speed of neutrinos:
 Today, at the Neutrino 2012 conference in Kyoto, Japan, the OPERA collaboration announced that according to their latest measurements, neutrinos travel at almost exactly the speed of light. "Although this result isn't as exciting as some would have liked, it is what we all expected deep down," said CERN research director Sergio Bertolucci in a statement.
It turns out that you don't have to know any physics whatsoever in order to understand this discovery, or to understand why it was inevitable. In fact, the explanation is pretty obvious from the article, although neither the author nor any of the physicists involved seem to have noticed it.

The article explains that last September, OPERA announced the discovery that neutrinos actually travel slightly faster than the speed of light (denoted by c)! The OPERA people were well aware that this result would overturn a century of fundamental physics, so they made sure to check very carefully that their result was correct. After being unable to find anything wrong with it, they announce it to the world. And the world was not willing to believe it.

So what happened next? A number of other labs tried to reproduce OPERA's result, and none of them were able to. So OPERA was shut down and their physicists returned to their previous farming occupations.

Just kidding. After OPERA realized no one was buying their schtick, they realized they had to retreat. Exactly what happened next is not completely clear. It appears they first did what the technical support people always tell us to do, namely they checked that their cables were connected well. And they found one that wasn't. So they fixed the cable, and the speed of neutrinos decreased, but not below c. So they looked further and found a faulty clock. Replacing the clock caused the speed of neutrinos to fall just slightly below c, which is where they wanted it to be.

So what did they do next? They next replaced every other piece of their equipment, one piece at a time, to see how sensitive the results were to the vagaries of their equipment. Just kidding again. Next, they did absolutely nothing except to announce their new result. Which just happened to be the result they expected. And was exactly the result I would expect to be achieved by people who keep jiggling their equipment until their output is on the right side of c, and then stop jiggling. Now I suppose one can say that the fact that their original result was close to c is strong evidence that the correct value is also close to c. But surely the subsequent jiggling gives us no further confidence that this is the case, and there is no good reason to take their new error bars seriously.

There is disagreement within OPERA about how much jiggling there should have been before they announced the earlier, unbelievable result. But everyone seems to agree that if a result is believable and even desirable, then it should be believed, and that no (further) jiggling is necessary.

For more fun with OPERAtic neutrinos, consider the following passage:
Before OPERA, all the evidence for neutrino oscillations came from disappearances: detectors would end up with less of a certain type of neutrino than they started with, suggesting some had morphed into other flavours. Then in 2010, OPERA found the first tau neutrino in a beam of billions of muon neutrinos streaming to the Gran Sasso detectors from CERN. The discovery was a big deal at the time, but the team said they needed more tau neutrinos to make it statistically significant. Now, a second tau neutrino has shown up in the detectors, they report.
In unrelated news, I recently conducted an exclusive interview with Joe, a janitor who works for OPERA. Joe told me that he remembers very well the day when the second tau neutrino was discovered.  "I remember that day" he explained, "because that was the day I badly sprained my ankle tripping over a cable."  "I should have been more careful" he added. "That was the second time that happened to me."

update: September 4, 2012
Innumerable people have written to ask me what I think about the discovery of the Higgs boson (or at least a particle very similar to the Higgs boson) by CERN.  According to Joe Incandela (probably not the Joe quoted above who used to work at OPERA), in order to discover this particle CERN had to observe a number of collisions comparable to the number of grains of sand that can fit in an Olympic size swimming pool.  In all those collisions, the elusive particle only showed up a few dozen times.

But it appeared nearly exactly the number of times and in exactly the way that the theory predicted.

Not clear.  But if so, this is a triumph. And if not,  it's even better because it's a "gateway" to Something New. Why should we believe all this? Because Scientists did the Math, and determined that the observations could not be due to  anything except this "God particle" (or something similar). Sort of like when Creationists do the Math and conclude that a new species could not have arisen except by some sort of ... God particle. Of course, scientists correctly point out that the math done by the Creationists fails to take into account certain alternative natural mechanisms. So exactly what mechanisms did the CERN Scientists take into account in order to rule out explanations alternative to their desired one? At last count I calculated that the Large Hadron Collider consists of a gazillion separate parts, each of which can malfunction in interesting ways.  Did anybody do the math here?  As of last September, we know the answer is "NO". (See footnote.)

But not to worry. This is a result everybody wanted, so what's not to like?

(Footnote: Perhaps malfunctioning equipment can cause an error in a measurement, but not in the detection of a particle. I doubt this, since I think everything is measurement. I haven't read the technical literature. But the best we can say about these scientists is that they are treating us like idiots. The worst we can say is ...)

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